2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007,
4 @c 2008, 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @section @acronym{POSIX} System Calls and Networking
12 * Conventions:: Conventions employed by the POSIX interface.
13 * Ports and File Descriptors:: Scheme ``ports'' and Unix file descriptors
14 have different representations.
15 * File System:: stat, chown, chmod, etc.
16 * User Information:: Retrieving a user's GECOS (/etc/passwd) entry.
17 * Time:: gettimeofday, localtime, strftime, etc.
18 * Runtime Environment:: Accessing and modifying Guile's environment.
19 * Processes:: getuid, getpid, etc.
20 * Signals:: sigaction, kill, pause, alarm, setitimer, etc.
21 * Terminals and Ptys:: ttyname, tcsetpgrp, etc.
22 * Pipes:: Communicating data between processes.
23 * Networking:: gethostbyaddr, getnetent, socket, bind, listen.
24 * System Identification:: Obtaining information about the system.
25 * Locales:: setlocale, etc.
30 @subsection @acronym{POSIX} Interface Conventions
32 These interfaces provide access to operating system facilities.
33 They provide a simple wrapping around the underlying C interfaces
34 to make usage from Scheme more convenient. They are also used
35 to implement the Guile port of scsh (@pxref{The Scheme shell (scsh)}).
37 Generally there is a single procedure for each corresponding Unix
38 facility. There are some exceptions, such as procedures implemented for
39 speed and convenience in Scheme with no primitive Unix equivalent,
40 e.g.@: @code{copy-file}.
42 The interfaces are intended as far as possible to be portable across
43 different versions of Unix. In some cases procedures which can't be
44 implemented on particular systems may become no-ops, or perform limited
45 actions. In other cases they may throw errors.
47 General naming conventions are as follows:
51 The Scheme name is often identical to the name of the underlying Unix
54 Underscores in Unix procedure names are converted to hyphens.
56 Procedures which destructively modify Scheme data have exclamation
57 marks appended, e.g., @code{recv!}.
59 Predicates (returning only @code{#t} or @code{#f}) have question marks
60 appended, e.g., @code{access?}.
62 Some names are changed to avoid conflict with dissimilar interfaces
63 defined by scsh, e.g., @code{primitive-fork}.
65 Unix preprocessor names such as @code{EPERM} or @code{R_OK} are converted
66 to Scheme variables of the same name (underscores are not replaced
70 Unexpected conditions are generally handled by raising exceptions.
71 There are a few procedures which return a special value if they don't
72 succeed, e.g., @code{getenv} returns @code{#f} if it the requested
73 string is not found in the environment. These cases are noted in
76 For ways to deal with exceptions, see @ref{Exceptions}.
79 Errors which the C library would report by returning a null pointer or
80 through some other means are reported by raising a @code{system-error}
81 exception with @code{scm-error} (@pxref{Error Reporting}). The
82 @var{data} parameter is a list containing the Unix @code{errno} value
83 (an integer). For example,
86 (define (my-handler key func fmt fmtargs data)
87 (display key) (newline)
88 (display func) (newline)
89 (apply format #t fmt fmtargs) (newline)
90 (display data) (newline))
93 (lambda () (dup2 -123 -456))
105 @defun system-error-errno arglist
107 Return the @code{errno} value from a list which is the arguments to an
108 exception handler. If the exception is not a @code{system-error},
109 then the return is @code{#f}. For example,
115 (mkdir "/this-ought-to-fail-if-I'm-not-root"))
117 (let ((errno (system-error-errno stuff)))
120 (display "You're not allowed to do that."))
122 (display "Already exists."))
124 (display (strerror errno))))
130 @node Ports and File Descriptors
131 @subsection Ports and File Descriptors
132 @cindex file descriptor
134 Conventions generally follow those of scsh, @ref{The Scheme shell (scsh)}.
136 File ports are implemented using low-level operating system I/O
137 facilities, with optional buffering to improve efficiency; see
140 Note that some procedures (e.g., @code{recv!}) will accept ports as
141 arguments, but will actually operate directly on the file descriptor
142 underlying the port. Any port buffering is ignored, including the
143 buffer which implements @code{peek-char} and @code{unread-char}.
145 The @code{force-output} and @code{drain-input} procedures can be used
146 to clear the buffers.
148 Each open file port has an associated operating system file descriptor.
149 File descriptors are generally not useful in Scheme programs; however
150 they may be needed when interfacing with foreign code and the Unix
153 A file descriptor can be extracted from a port and a new port can be
154 created from a file descriptor. However a file descriptor is just an
155 integer and the garbage collector doesn't recognize it as a reference
156 to the port. If all other references to the port were dropped, then
157 it's likely that the garbage collector would free the port, with the
158 side-effect of closing the file descriptor prematurely.
160 To assist the programmer in avoiding this problem, each port has an
161 associated @dfn{revealed count} which can be used to keep track of how many
162 times the underlying file descriptor has been stored in other places.
163 If a port's revealed count is greater than zero, the file descriptor
164 will not be closed when the port is garbage collected. A programmer
165 can therefore ensure that the revealed count will be greater than
166 zero if the file descriptor is needed elsewhere.
168 For the simple case where a file descriptor is ``imported'' once to become
169 a port, it does not matter if the file descriptor is closed when the
170 port is garbage collected. There is no need to maintain a revealed
171 count. Likewise when ``exporting'' a file descriptor to the external
172 environment, setting the revealed count is not required provided the
173 port is kept open (i.e., is pointed to by a live Scheme binding) while
174 the file descriptor is in use.
176 To correspond with traditional Unix behaviour, three file descriptors
177 (0, 1, and 2) are automatically imported when a program starts up and
178 assigned to the initial values of the current/standard input, output,
179 and error ports, respectively. The revealed count for each is
180 initially set to one, so that dropping references to one of these
181 ports will not result in its garbage collection: it could be retrieved
182 with @code{fdopen} or @code{fdes->ports}.
184 @deffn {Scheme Procedure} port-revealed port
185 @deffnx {C Function} scm_port_revealed (port)
186 Return the revealed count for @var{port}.
189 @deffn {Scheme Procedure} set-port-revealed! port rcount
190 @deffnx {C Function} scm_set_port_revealed_x (port, rcount)
191 Sets the revealed count for a @var{port} to @var{rcount}.
192 The return value is unspecified.
195 @deffn {Scheme Procedure} fileno port
196 @deffnx {C Function} scm_fileno (port)
197 Return the integer file descriptor underlying @var{port}. Does
198 not change its revealed count.
201 @deffn {Scheme Procedure} port->fdes port
202 Returns the integer file descriptor underlying @var{port}. As a
203 side effect the revealed count of @var{port} is incremented.
206 @deffn {Scheme Procedure} fdopen fdes modes
207 @deffnx {C Function} scm_fdopen (fdes, modes)
208 Return a new port based on the file descriptor @var{fdes}. Modes are
209 given by the string @var{modes}. The revealed count of the port is
210 initialized to zero. The @var{modes} string is the same as that
211 accepted by @code{open-file} (@pxref{File Ports, open-file}).
214 @deffn {Scheme Procedure} fdes->ports fdes
215 @deffnx {C Function} scm_fdes_to_ports (fdes)
216 Return a list of existing ports which have @var{fdes} as an
217 underlying file descriptor, without changing their revealed
221 @deffn {Scheme Procedure} fdes->inport fdes
222 Returns an existing input port which has @var{fdes} as its underlying file
223 descriptor, if one exists, and increments its revealed count.
224 Otherwise, returns a new input port with a revealed count of 1.
227 @deffn {Scheme Procedure} fdes->outport fdes
228 Returns an existing output port which has @var{fdes} as its underlying file
229 descriptor, if one exists, and increments its revealed count.
230 Otherwise, returns a new output port with a revealed count of 1.
233 @deffn {Scheme Procedure} primitive-move->fdes port fdes
234 @deffnx {C Function} scm_primitive_move_to_fdes (port, fdes)
235 Moves the underlying file descriptor for @var{port} to the integer
236 value @var{fdes} without changing the revealed count of @var{port}.
237 Any other ports already using this descriptor will be automatically
238 shifted to new descriptors and their revealed counts reset to zero.
239 The return value is @code{#f} if the file descriptor already had the
240 required value or @code{#t} if it was moved.
243 @deffn {Scheme Procedure} move->fdes port fdes
244 Moves the underlying file descriptor for @var{port} to the integer
245 value @var{fdes} and sets its revealed count to one. Any other ports
246 already using this descriptor will be automatically
247 shifted to new descriptors and their revealed counts reset to zero.
248 The return value is unspecified.
251 @deffn {Scheme Procedure} release-port-handle port
252 Decrements the revealed count for a port.
255 @deffn {Scheme Procedure} fsync port_or_fd
256 @deffnx {C Function} scm_fsync (port_or_fd)
257 Copies any unwritten data for the specified output file descriptor to disk.
258 If @var{port_or_fd} is a port, its buffer is flushed before the underlying
259 file descriptor is fsync'd.
260 The return value is unspecified.
263 @deffn {Scheme Procedure} open path flags [mode]
264 @deffnx {C Function} scm_open (path, flags, mode)
265 Open the file named by @var{path} for reading and/or writing.
266 @var{flags} is an integer specifying how the file should be opened.
267 @var{mode} is an integer specifying the permission bits of the file,
268 if it needs to be created, before the umask (@pxref{Processes}) is
269 applied. The default is 666 (Unix itself has no default).
271 @var{flags} can be constructed by combining variables using @code{logior}.
275 Open the file read-only.
278 Open the file write-only.
281 Open the file read/write.
284 Append to the file instead of truncating.
287 Create the file if it does not already exist.
290 @xref{File Status Flags,,,libc,The GNU C Library Reference Manual},
291 for additional flags.
294 @deffn {Scheme Procedure} open-fdes path flags [mode]
295 @deffnx {C Function} scm_open_fdes (path, flags, mode)
296 Similar to @code{open} but return a file descriptor instead of
300 @deffn {Scheme Procedure} close fd_or_port
301 @deffnx {C Function} scm_close (fd_or_port)
302 Similar to @code{close-port} (@pxref{Closing, close-port}),
303 but also works on file descriptors. A side
304 effect of closing a file descriptor is that any ports using that file
305 descriptor are moved to a different file descriptor and have
306 their revealed counts set to zero.
309 @deffn {Scheme Procedure} close-fdes fd
310 @deffnx {C Function} scm_close_fdes (fd)
311 A simple wrapper for the @code{close} system call. Close file
312 descriptor @var{fd}, which must be an integer. Unlike @code{close},
313 the file descriptor will be closed even if a port is using it. The
314 return value is unspecified.
317 @deffn {Scheme Procedure} unread-char char [port]
318 @deffnx {C Function} scm_unread_char (char, port)
319 Place @var{char} in @var{port} so that it will be read by the next
320 read operation on that port. If called multiple times, the unread
321 characters will be read again in ``last-in, first-out'' order (i.e.@:
322 a stack). If @var{port} is not supplied, the current input port is
326 @deffn {Scheme Procedure} unread-string str port
327 Place the string @var{str} in @var{port} so that its characters will be
328 read in subsequent read operations. If called multiple times, the
329 unread characters will be read again in last-in first-out order. If
330 @var{port} is not supplied, the current-input-port is used.
333 @deffn {Scheme Procedure} pipe
334 @deffnx {C Function} scm_pipe ()
336 Return a newly created pipe: a pair of ports which are linked
337 together on the local machine. The @acronym{CAR} is the input
338 port and the @acronym{CDR} is the output port. Data written (and
339 flushed) to the output port can be read from the input port.
340 Pipes are commonly used for communication with a newly forked
341 child process. The need to flush the output port can be
342 avoided by making it unbuffered using @code{setvbuf}.
345 A write of up to @code{PIPE_BUF} many bytes to a pipe is atomic,
346 meaning when done it goes into the pipe instantaneously and as a
347 contiguous block (@pxref{Pipe Atomicity,, Atomicity of Pipe I/O, libc,
348 The GNU C Library Reference Manual}).
351 Note that the output port is likely to block if too much data has been
352 written but not yet read from the input port. Typically the capacity
353 is @code{PIPE_BUF} bytes.
356 The next group of procedures perform a @code{dup2}
357 system call, if @var{newfd} (an
358 integer) is supplied, otherwise a @code{dup}. The file descriptor to be
359 duplicated can be supplied as an integer or contained in a port. The
360 type of value returned varies depending on which procedure is used.
362 All procedures also have the side effect when performing @code{dup2} that any
363 ports using @var{newfd} are moved to a different file descriptor and have
364 their revealed counts set to zero.
366 @deffn {Scheme Procedure} dup->fdes fd_or_port [fd]
367 @deffnx {C Function} scm_dup_to_fdes (fd_or_port, fd)
368 Return a new integer file descriptor referring to the open file
369 designated by @var{fd_or_port}, which must be either an open
370 file port or a file descriptor.
373 @deffn {Scheme Procedure} dup->inport port/fd [newfd]
374 Returns a new input port using the new file descriptor.
377 @deffn {Scheme Procedure} dup->outport port/fd [newfd]
378 Returns a new output port using the new file descriptor.
381 @deffn {Scheme Procedure} dup port/fd [newfd]
382 Returns a new port if @var{port/fd} is a port, with the same mode as the
383 supplied port, otherwise returns an integer file descriptor.
386 @deffn {Scheme Procedure} dup->port port/fd mode [newfd]
387 Returns a new port using the new file descriptor. @var{mode} supplies a
388 mode string for the port (@pxref{File Ports, open-file}).
391 @deffn {Scheme Procedure} duplicate-port port modes
392 Returns a new port which is opened on a duplicate of the file
393 descriptor underlying @var{port}, with mode string @var{modes}
394 as for @ref{File Ports, open-file}. The two ports
395 will share a file position and file status flags.
397 Unexpected behaviour can result if both ports are subsequently used
398 and the original and/or duplicate ports are buffered.
399 The mode string can include @code{0} to obtain an unbuffered duplicate
402 This procedure is equivalent to @code{(dup->port @var{port} @var{modes})}.
405 @deffn {Scheme Procedure} redirect-port old_port new_port
406 @deffnx {C Function} scm_redirect_port (old_port, new_port)
407 This procedure takes two ports and duplicates the underlying file
408 descriptor from @var{old_port} into @var{new_port}. The
409 current file descriptor in @var{new_port} will be closed.
410 After the redirection the two ports will share a file position
411 and file status flags.
413 The return value is unspecified.
415 Unexpected behaviour can result if both ports are subsequently used
416 and the original and/or duplicate ports are buffered.
418 This procedure does not have any side effects on other ports or
422 @deffn {Scheme Procedure} dup2 oldfd newfd
423 @deffnx {C Function} scm_dup2 (oldfd, newfd)
424 A simple wrapper for the @code{dup2} system call.
425 Copies the file descriptor @var{oldfd} to descriptor
426 number @var{newfd}, replacing the previous meaning
427 of @var{newfd}. Both @var{oldfd} and @var{newfd} must
429 Unlike for @code{dup->fdes} or @code{primitive-move->fdes}, no attempt
430 is made to move away ports which are using @var{newfd}.
431 The return value is unspecified.
434 @deffn {Scheme Procedure} port-mode port
435 Return the port modes associated with the open port @var{port}.
436 These will not necessarily be identical to the modes used when
437 the port was opened, since modes such as ``append'' which are
438 used only during port creation are not retained.
441 @deffn {Scheme Procedure} port-for-each proc
442 @deffnx {C Function} scm_port_for_each (SCM proc)
443 @deffnx {C Function} scm_c_port_for_each (void (*proc)(void *, SCM), void *data)
444 Apply @var{proc} to each port in the Guile port table
445 (FIXME: what is the Guile port table?)
446 in turn. The return value is unspecified. More specifically,
447 @var{proc} is applied exactly once to every port that exists in the
448 system at the time @code{port-for-each} is invoked. Changes to the
449 port table while @code{port-for-each} is running have no effect as far
450 as @code{port-for-each} is concerned.
452 The C function @code{scm_port_for_each} takes a Scheme procedure
453 encoded as a @code{SCM} value, while @code{scm_c_port_for_each} takes
454 a pointer to a C function and passes along a arbitrary @var{data}
458 @deffn {Scheme Procedure} setvbuf port mode [size]
459 @deffnx {C Function} scm_setvbuf (port, mode, size)
460 @cindex port buffering
461 Set the buffering mode for @var{port}. @var{mode} can be:
470 block buffered, using a newly allocated buffer of @var{size} bytes.
471 If @var{size} is omitted, a default size will be used.
474 Only certain types of ports are supported, most importantly
478 @deffn {Scheme Procedure} fcntl port/fd cmd [value]
479 @deffnx {C Function} scm_fcntl (object, cmd, value)
480 Apply @var{cmd} on @var{port/fd}, either a port or file descriptor.
481 The @var{value} argument is used by the @code{SET} commands described
482 below, it's an integer value.
484 Values for @var{cmd} are:
487 Duplicate the file descriptor, the same as @code{dup->fdes} above
493 Get or set flags associated with the file descriptor. The only flag
497 ``Close on exec'', meaning the file descriptor will be closed on an
498 @code{exec} call (a successful such call). For example to set that
502 (fcntl port F_SETFD FD_CLOEXEC)
505 Or better, set it but leave any other possible future flags unchanged,
508 (fcntl port F_SETFD (logior FD_CLOEXEC
509 (fcntl port F_GETFD)))
516 Get or set flags associated with the open file. These flags are
517 @code{O_RDONLY} etc described under @code{open} above.
519 A common use is to set @code{O_NONBLOCK} on a network socket. The
520 following sets that flag, and leaves other flags unchanged.
523 (fcntl sock F_SETFL (logior O_NONBLOCK
524 (fcntl sock F_GETFL)))
530 Get or set the process ID of a socket's owner, for @code{SIGIO} signals.
534 @deffn {Scheme Procedure} flock file operation
535 @deffnx {C Function} scm_flock (file, operation)
537 Apply or remove an advisory lock on an open file.
538 @var{operation} specifies the action to be done:
541 Shared lock. More than one process may hold a shared lock
542 for a given file at a given time.
545 Exclusive lock. Only one process may hold an exclusive lock
546 for a given file at a given time.
552 Don't block when locking. This is combined with one of the other
553 operations using @code{logior} (@pxref{Bitwise Operations}). If
554 @code{flock} would block an @code{EWOULDBLOCK} error is thrown
555 (@pxref{Conventions}).
558 The return value is not specified. @var{file} may be an open
559 file descriptor or an open file descriptor port.
561 Note that @code{flock} does not lock files across NFS.
564 @deffn {Scheme Procedure} select reads writes excepts [secs [usecs]]
565 @deffnx {C Function} scm_select (reads, writes, excepts, secs, usecs)
566 This procedure has a variety of uses: waiting for the ability
567 to provide input, accept output, or the existence of
568 exceptional conditions on a collection of ports or file
569 descriptors, or waiting for a timeout to occur.
571 When an error occurs, of if it is interrupted by a signal, this
572 procedure throws a @code{system-error} exception
573 (@pxref{Conventions, @code{system-error}}). In case of an
574 interruption, the associated error number is @var{EINTR}.
576 @var{reads}, @var{writes} and @var{excepts} can be lists or
577 vectors, with each member a port or a file descriptor.
578 The value returned is a list of three corresponding
579 lists or vectors containing only the members which meet the
580 specified requirement. The ability of port buffers to
581 provide input or accept output is taken into account.
582 Ordering of the input lists or vectors is not preserved.
584 The optional arguments @var{secs} and @var{usecs} specify the
585 timeout. Either @var{secs} can be specified alone, as
586 either an integer or a real number, or both @var{secs} and
587 @var{usecs} can be specified as integers, in which case
588 @var{usecs} is an additional timeout expressed in
589 microseconds. If @var{secs} is omitted or is @code{#f} then
590 select will wait for as long as it takes for one of the other
591 conditions to be satisfied.
593 The scsh version of @code{select} differs as follows:
594 Only vectors are accepted for the first three arguments.
595 The @var{usecs} argument is not supported.
596 Multiple values are returned instead of a list.
597 Duplicates in the input vectors appear only once in output.
598 An additional @code{select!} interface is provided.
602 @subsection File System
605 These procedures allow querying and setting file system attributes
607 permissions, sizes and types of files); deleting, copying, renaming and
608 linking files; creating and removing directories and querying their
609 contents; syncing the file system and creating special files.
611 @deffn {Scheme Procedure} access? path how
612 @deffnx {C Function} scm_access (path, how)
613 Test accessibility of a file under the real UID and GID of the calling
614 process. The return is @code{#t} if @var{path} exists and the
615 permissions requested by @var{how} are all allowed, or @code{#f} if
618 @var{how} is an integer which is one of the following values, or a
619 bitwise-OR (@code{logior}) of multiple values.
622 Test for read permission.
625 Test for write permission.
628 Test for execute permission.
631 Test for existence of the file. This is implied by each of the other
632 tests, so there's no need to combine it with them.
635 It's important to note that @code{access?} does not simply indicate
636 what will happen on attempting to read or write a file. In normal
637 circumstances it does, but in a set-UID or set-GID program it doesn't
638 because @code{access?} tests the real ID, whereas an open or execute
639 attempt uses the effective ID.
641 A program which will never run set-UID/GID can ignore the difference
642 between real and effective IDs, but for maximum generality, especially
643 in library functions, it's best not to use @code{access?} to predict
644 the result of an open or execute, instead simply attempt that and
647 The main use for @code{access?} is to let a set-UID/GID program
648 determine what the invoking user would have been allowed to do,
649 without the greater (or perhaps lesser) privileges afforded by the
650 effective ID. For more on this, see @ref{Testing File Access,,, libc,
651 The GNU C Library Reference Manual}.
655 @deffn {Scheme Procedure} stat object
656 @deffnx {C Function} scm_stat (object)
657 Return an object containing various information about the file
658 determined by @var{object}. @var{object} can be a string containing
659 a file name or a port or integer file descriptor which is open
660 on a file (in which case @code{fstat} is used as the underlying
663 The object returned by @code{stat} can be passed as a single
664 parameter to the following procedures, all of which return
667 @deffn {Scheme Procedure} stat:dev st
668 The device number containing the file.
670 @deffn {Scheme Procedure} stat:ino st
671 The file serial number, which distinguishes this file from all
672 other files on the same device.
674 @deffn {Scheme Procedure} stat:mode st
675 The mode of the file. This is an integer which incorporates file type
676 information and file permission bits. See also @code{stat:type} and
677 @code{stat:perms} below.
679 @deffn {Scheme Procedure} stat:nlink st
680 The number of hard links to the file.
682 @deffn {Scheme Procedure} stat:uid st
683 The user ID of the file's owner.
685 @deffn {Scheme Procedure} stat:gid st
686 The group ID of the file.
688 @deffn {Scheme Procedure} stat:rdev st
689 Device ID; this entry is defined only for character or block special
690 files. On some systems this field is not available at all, in which
691 case @code{stat:rdev} returns @code{#f}.
693 @deffn {Scheme Procedure} stat:size st
694 The size of a regular file in bytes.
696 @deffn {Scheme Procedure} stat:atime st
697 The last access time for the file, in seconds.
699 @deffn {Scheme Procedure} stat:mtime st
700 The last modification time for the file, in seconds.
702 @deffn {Scheme Procedure} stat:ctime st
703 The last modification time for the attributes of the file, in seconds.
705 @deffn {Scheme Procedure} stat:atimensec st
706 @deffnx {Scheme Procedure} stat:mtimensec st
707 @deffnx {Scheme Procedure} stat:ctimensec st
708 The fractional part of a file's access, modification, or attribute modification
709 time, in nanoseconds. Nanosecond timestamps are only available on some operating
710 systems and file systems. If Guile cannot retrieve nanosecond-level timestamps
711 for a file, these fields will be set to 0.
713 @deffn {Scheme Procedure} stat:blksize st
714 The optimal block size for reading or writing the file, in bytes. On
715 some systems this field is not available, in which case
716 @code{stat:blksize} returns a sensible suggested block size.
718 @deffn {Scheme Procedure} stat:blocks st
719 The amount of disk space that the file occupies measured in units of
720 512 byte blocks. On some systems this field is not available, in
721 which case @code{stat:blocks} returns @code{#f}.
724 In addition, the following procedures return the information
725 from @code{stat:mode} in a more convenient form:
727 @deffn {Scheme Procedure} stat:type st
728 A symbol representing the type of file. Possible values are
729 @samp{regular}, @samp{directory}, @samp{symlink},
730 @samp{block-special}, @samp{char-special}, @samp{fifo}, @samp{socket},
733 @deffn {Scheme Procedure} stat:perms st
734 An integer representing the access permission bits.
738 @deffn {Scheme Procedure} lstat path
739 @deffnx {C Function} scm_lstat (path)
740 Similar to @code{stat}, but does not follow symbolic links, i.e.,
741 it will return information about a symbolic link itself, not the
742 file it points to. @var{path} must be a string.
745 @deffn {Scheme Procedure} readlink path
746 @deffnx {C Function} scm_readlink (path)
747 Return the value of the symbolic link named by @var{path} (a
748 string), i.e., the file that the link points to.
753 @deffn {Scheme Procedure} chown object owner group
754 @deffnx {C Function} scm_chown (object, owner, group)
755 Change the ownership and group of the file referred to by @var{object}
756 to the integer values @var{owner} and @var{group}. @var{object} can
757 be a string containing a file name or, if the platform supports
758 @code{fchown} (@pxref{File Owner,,,libc,The GNU C Library Reference
759 Manual}), a port or integer file descriptor which is open on the file.
760 The return value is unspecified.
762 If @var{object} is a symbolic link, either the
763 ownership of the link or the ownership of the referenced file will be
764 changed depending on the operating system (lchown is
765 unsupported at present). If @var{owner} or @var{group} is specified
766 as @code{-1}, then that ID is not changed.
770 @deffn {Scheme Procedure} chmod object mode
771 @deffnx {C Function} scm_chmod (object, mode)
772 Changes the permissions of the file referred to by @var{object}.
773 @var{object} can be a string containing a file name or a port or integer file
774 descriptor which is open on a file (in which case @code{fchmod} is used
775 as the underlying system call).
777 the new permissions as a decimal number, e.g., @code{(chmod "foo" #o755)}.
778 The return value is unspecified.
781 @deffn {Scheme Procedure} utime pathname [actime [modtime [actimens [modtimens [flags]]]]]
782 @deffnx {C Function} scm_utime (pathname, actime, modtime, actimens, modtimens, flags)
783 @code{utime} sets the access and modification times for the
784 file named by @var{pathname}. If @var{actime} or @var{modtime} is
785 not supplied, then the current time is used. @var{actime} and
786 @var{modtime} must be integer time values as returned by the
787 @code{current-time} procedure.
789 The optional @var{actimens} and @var{modtimens} are nanoseconds
790 to add @var{actime} and @var{modtime}. Nanosecond precision is
791 only supported on some combinations of file systems and operating
794 (utime "foo" (- (current-time) 3600))
796 will set the access time to one hour in the past and the
797 modification time to the current time.
801 @deffn {Scheme Procedure} delete-file str
802 @deffnx {C Function} scm_delete_file (str)
803 Deletes (or ``unlinks'') the file whose path is specified by
807 @deffn {Scheme Procedure} copy-file oldfile newfile
808 @deffnx {C Function} scm_copy_file (oldfile, newfile)
809 Copy the file specified by @var{oldfile} to @var{newfile}.
810 The return value is unspecified.
813 @deffn {Scheme Procedure} sendfile out in count [offset]
814 @deffnx {C Function} scm_sendfile (out, in, count, offset)
815 Send @var{count} bytes from @var{in} to @var{out}, both of which
816 must be either open file ports or file descriptors. When
817 @var{offset} is omitted, start reading from @var{in}'s current
818 position; otherwise, start reading at @var{offset}. Return
819 the number of bytes actually sent.
821 When @var{in} is a port, it is often preferable to specify @var{offset},
822 because @var{in}'s offset as a port may be different from the offset of
823 its underlying file descriptor.
825 On systems that support it, such as GNU/Linux, this procedure uses the
826 @code{sendfile} libc function, which usually corresponds to a system
827 call. This is faster than doing a series of @code{read} and
828 @code{write} system calls. A typical application is to send a file over
831 In some cases, the @code{sendfile} libc function may return
832 @code{EINVAL} or @code{ENOSYS}. In that case, Guile's @code{sendfile}
833 procedure automatically falls back to doing a series of @code{read} and
836 In other cases, the libc function may send fewer bytes than
837 @var{count}---for instance because @var{out} is a slow or limited
838 device, such as a pipe. When that happens, Guile's @code{sendfile}
839 automatically retries until exactly @var{count} bytes were sent or an
844 @deffn {Scheme Procedure} rename-file oldname newname
845 @deffnx {C Function} scm_rename (oldname, newname)
846 Renames the file specified by @var{oldname} to @var{newname}.
847 The return value is unspecified.
850 @deffn {Scheme Procedure} link oldpath newpath
851 @deffnx {C Function} scm_link (oldpath, newpath)
852 Creates a new name @var{newpath} in the file system for the
853 file named by @var{oldpath}. If @var{oldpath} is a symbolic
854 link, the link may or may not be followed depending on the
858 @deffn {Scheme Procedure} symlink oldpath newpath
859 @deffnx {C Function} scm_symlink (oldpath, newpath)
860 Create a symbolic link named @var{newpath} with the value (i.e., pointing to)
861 @var{oldpath}. The return value is unspecified.
864 @deffn {Scheme Procedure} mkdir path [mode]
865 @deffnx {C Function} scm_mkdir (path, mode)
866 Create a new directory named by @var{path}. If @var{mode} is omitted
867 then the permissions of the directory file are set using the current
868 umask (@pxref{Processes}). Otherwise they are set to the decimal
869 value specified with @var{mode}. The return value is unspecified.
872 @deffn {Scheme Procedure} rmdir path
873 @deffnx {C Function} scm_rmdir (path)
874 Remove the existing directory named by @var{path}. The directory must
875 be empty for this to succeed. The return value is unspecified.
878 @deffn {Scheme Procedure} opendir dirname
879 @deffnx {C Function} scm_opendir (dirname)
880 @cindex directory contents
881 Open the directory specified by @var{dirname} and return a directory
884 Before using this and the procedures below, make sure to see the
885 higher-level procedures for directory traversal that are available
886 (@pxref{File Tree Walk}).
889 @deffn {Scheme Procedure} directory-stream? object
890 @deffnx {C Function} scm_directory_stream_p (object)
891 Return a boolean indicating whether @var{object} is a directory
892 stream as returned by @code{opendir}.
895 @deffn {Scheme Procedure} readdir stream
896 @deffnx {C Function} scm_readdir (stream)
897 Return (as a string) the next directory entry from the directory stream
898 @var{stream}. If there is no remaining entry to be read then the
899 end of file object is returned.
902 @deffn {Scheme Procedure} rewinddir stream
903 @deffnx {C Function} scm_rewinddir (stream)
904 Reset the directory port @var{stream} so that the next call to
905 @code{readdir} will return the first directory entry.
908 @deffn {Scheme Procedure} closedir stream
909 @deffnx {C Function} scm_closedir (stream)
910 Close the directory stream @var{stream}.
911 The return value is unspecified.
914 Here is an example showing how to display all the entries in a
918 (define dir (opendir "/usr/lib"))
919 (do ((entry (readdir dir) (readdir dir)))
920 ((eof-object? entry))
921 (display entry)(newline))
925 @deffn {Scheme Procedure} sync
926 @deffnx {C Function} scm_sync ()
927 Flush the operating system disk buffers.
928 The return value is unspecified.
931 @deffn {Scheme Procedure} mknod path type perms dev
932 @deffnx {C Function} scm_mknod (path, type, perms, dev)
934 Creates a new special file, such as a file corresponding to a device.
935 @var{path} specifies the name of the file. @var{type} should be one
936 of the following symbols: @samp{regular}, @samp{directory},
937 @samp{symlink}, @samp{block-special}, @samp{char-special},
938 @samp{fifo}, or @samp{socket}. @var{perms} (an integer) specifies the
939 file permissions. @var{dev} (an integer) specifies which device the
940 special file refers to. Its exact interpretation depends on the kind
941 of special file being created.
945 (mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))
948 The return value is unspecified.
951 @deffn {Scheme Procedure} tmpnam
952 @deffnx {C Function} scm_tmpnam ()
953 @cindex temporary file
954 Return an auto-generated name of a temporary file, a file which
955 doesn't already exist. The name includes a path, it's usually in
956 @file{/tmp} but that's system dependent.
958 Care must be taken when using @code{tmpnam}. In between choosing the
959 name and creating the file another program might use that name, or an
960 attacker might even make it a symlink pointing at something important
961 and causing you to overwrite that.
963 The safe way is to create the file using @code{open} with
964 @code{O_EXCL} to avoid any overwriting. A loop can try again with
965 another name if the file exists (error @code{EEXIST}).
966 @code{mkstemp!} below does that.
969 @deffn {Scheme Procedure} mkstemp! tmpl
970 @deffnx {C Function} scm_mkstemp (tmpl)
971 @cindex temporary file
972 Create a new unique file in the file system and return a new buffered
973 port open for reading and writing to the file.
975 @var{tmpl} is a string specifying where the file should be created: it
976 must end with @samp{XXXXXX} and those @samp{X}s will be changed in the
977 string to return the name of the file. (@code{port-filename} on the
978 port also gives the name.)
980 POSIX doesn't specify the permissions mode of the file, on GNU and
981 most systems it's @code{#o600}. An application can use @code{chmod}
982 to relax that if desired. For example @code{#o666} less @code{umask},
983 which is usual for ordinary file creation,
986 (let ((port (mkstemp! (string-copy "/tmp/myfile-XXXXXX"))))
987 (chmod port (logand #o666 (lognot (umask))))
992 @deffn {Scheme Procedure} tmpfile
993 @deffnx {C Function} scm_tmpfile ()
994 Return an input/output port to a unique temporary file
995 named using the path prefix @code{P_tmpdir} defined in
997 The file is automatically deleted when the port is closed
998 or the program terminates.
1001 @deffn {Scheme Procedure} dirname filename
1002 @deffnx {C Function} scm_dirname (filename)
1003 Return the directory name component of the file name
1004 @var{filename}. If @var{filename} does not contain a directory
1005 component, @code{.} is returned.
1008 @deffn {Scheme Procedure} basename filename [suffix]
1009 @deffnx {C Function} scm_basename (filename, suffix)
1010 Return the base name of the file name @var{filename}. The
1011 base name is the file name without any directory components.
1012 If @var{suffix} is provided, and is equal to the end of
1013 @var{basename}, it is removed also.
1016 (basename "/tmp/test.xml" ".xml")
1021 @deffn {Scheme Procedure} file-exists? filename
1022 Return @code{#t} if the file named @var{filename} exists, @code{#f} if
1026 @cindex file name separator
1027 @cindex absolute file name
1029 Many operating systems, such as GNU, use @code{/} (forward slash) to
1030 separate the components of a file name; any file name starting with
1031 @code{/} is considered an @dfn{absolute file name}. These conventions
1032 are specified by the POSIX Base Definitions, which refer to conforming
1033 file names as ``pathnames''. Some operating systems use a different
1034 convention; in particular, Windows uses @code{\} (backslash) as the file
1035 name separator, and also has the notion of @dfn{volume names} like
1036 @code{C:\} for absolute file names. The following procedures and
1037 variables provide support for portable file name manipulations.
1039 @deffn {Scheme Procedure} system-file-name-convention
1040 Return either @code{posix} or @code{windows}, depending on
1041 what kind of system this Guile is running on.
1044 @deffn {Scheme Procedure} file-name-separator? c
1045 Return true if character @var{c} is a file name separator on the host
1049 @deffn {Scheme Procedure} absolute-file-name? file-name
1050 Return true if @var{file-name} denotes an absolute file name on the host
1054 @defvr {Scheme Variable} file-name-separator-string
1055 The preferred file name separator.
1057 Note that on MinGW builds for Windows, both @code{/} and @code{\} are
1058 valid separators. Thus, programs should not assume that
1059 @code{file-name-separator-string} is the @emph{only} file name
1060 separator---e.g., when extracting the components of a file name.
1064 @node User Information
1065 @subsection User Information
1066 @cindex user information
1067 @cindex password file
1070 The facilities in this section provide an interface to the user and
1072 They should be used with care since they are not reentrant.
1074 The following functions accept an object representing user information
1075 and return a selected component:
1077 @deffn {Scheme Procedure} passwd:name pw
1078 The name of the userid.
1080 @deffn {Scheme Procedure} passwd:passwd pw
1081 The encrypted passwd.
1083 @deffn {Scheme Procedure} passwd:uid pw
1086 @deffn {Scheme Procedure} passwd:gid pw
1087 The group id number.
1089 @deffn {Scheme Procedure} passwd:gecos pw
1092 @deffn {Scheme Procedure} passwd:dir pw
1095 @deffn {Scheme Procedure} passwd:shell pw
1100 @deffn {Scheme Procedure} getpwuid uid
1101 Look up an integer userid in the user database.
1104 @deffn {Scheme Procedure} getpwnam name
1105 Look up a user name string in the user database.
1108 @deffn {Scheme Procedure} setpwent
1109 Initializes a stream used by @code{getpwent} to read from the user database.
1110 The next use of @code{getpwent} will return the first entry. The
1111 return value is unspecified.
1114 @deffn {Scheme Procedure} getpwent
1115 Read the next entry in the user database stream. The return is a
1116 passwd user object as above, or @code{#f} when no more entries.
1119 @deffn {Scheme Procedure} endpwent
1120 Closes the stream used by @code{getpwent}. The return value is unspecified.
1123 @deffn {Scheme Procedure} setpw [arg]
1124 @deffnx {C Function} scm_setpwent (arg)
1125 If called with a true argument, initialize or reset the password data
1126 stream. Otherwise, close the stream. The @code{setpwent} and
1127 @code{endpwent} procedures are implemented on top of this.
1130 @deffn {Scheme Procedure} getpw [user]
1131 @deffnx {C Function} scm_getpwuid (user)
1132 Look up an entry in the user database. @var{user} can be an integer,
1133 a string, or omitted, giving the behaviour of getpwuid, getpwnam
1134 or getpwent respectively.
1137 The following functions accept an object representing group information
1138 and return a selected component:
1140 @deffn {Scheme Procedure} group:name gr
1143 @deffn {Scheme Procedure} group:passwd gr
1144 The encrypted group password.
1146 @deffn {Scheme Procedure} group:gid gr
1147 The group id number.
1149 @deffn {Scheme Procedure} group:mem gr
1150 A list of userids which have this group as a supplementary group.
1154 @deffn {Scheme Procedure} getgrgid gid
1155 Look up an integer group id in the group database.
1158 @deffn {Scheme Procedure} getgrnam name
1159 Look up a group name in the group database.
1162 @deffn {Scheme Procedure} setgrent
1163 Initializes a stream used by @code{getgrent} to read from the group database.
1164 The next use of @code{getgrent} will return the first entry.
1165 The return value is unspecified.
1168 @deffn {Scheme Procedure} getgrent
1169 Return the next entry in the group database, using the stream set by
1173 @deffn {Scheme Procedure} endgrent
1174 Closes the stream used by @code{getgrent}.
1175 The return value is unspecified.
1178 @deffn {Scheme Procedure} setgr [arg]
1179 @deffnx {C Function} scm_setgrent (arg)
1180 If called with a true argument, initialize or reset the group data
1181 stream. Otherwise, close the stream. The @code{setgrent} and
1182 @code{endgrent} procedures are implemented on top of this.
1185 @deffn {Scheme Procedure} getgr [group]
1186 @deffnx {C Function} scm_getgrgid (group)
1187 Look up an entry in the group database. @var{group} can be an integer,
1188 a string, or omitted, giving the behaviour of getgrgid, getgrnam
1189 or getgrent respectively.
1192 In addition to the accessor procedures for the user database, the
1193 following shortcut procedure is also available.
1195 @deffn {Scheme Procedure} getlogin
1196 @deffnx {C Function} scm_getlogin ()
1197 Return a string containing the name of the user logged in on
1198 the controlling terminal of the process, or @code{#f} if this
1199 information cannot be obtained.
1207 @deffn {Scheme Procedure} current-time
1208 @deffnx {C Function} scm_current_time ()
1209 Return the number of seconds since 1970-01-01 00:00:00 @acronym{UTC},
1210 excluding leap seconds.
1213 @deffn {Scheme Procedure} gettimeofday
1214 @deffnx {C Function} scm_gettimeofday ()
1215 Return a pair containing the number of seconds and microseconds
1216 since 1970-01-01 00:00:00 @acronym{UTC}, excluding leap seconds. Note:
1217 whether true microsecond resolution is available depends on the
1221 The following procedures either accept an object representing a broken down
1222 time and return a selected component, or accept an object representing
1223 a broken down time and a value and set the component to the value.
1224 The numbers in parentheses give the usual range.
1226 @deffn {Scheme Procedure} tm:sec tm
1227 @deffnx {Scheme Procedure} set-tm:sec tm val
1230 @deffn {Scheme Procedure} tm:min tm
1231 @deffnx {Scheme Procedure} set-tm:min tm val
1234 @deffn {Scheme Procedure} tm:hour tm
1235 @deffnx {Scheme Procedure} set-tm:hour tm val
1238 @deffn {Scheme Procedure} tm:mday tm
1239 @deffnx {Scheme Procedure} set-tm:mday tm val
1240 Day of the month (1-31).
1242 @deffn {Scheme Procedure} tm:mon tm
1243 @deffnx {Scheme Procedure} set-tm:mon tm val
1246 @deffn {Scheme Procedure} tm:year tm
1247 @deffnx {Scheme Procedure} set-tm:year tm val
1248 Year (70-), the year minus 1900.
1250 @deffn {Scheme Procedure} tm:wday tm
1251 @deffnx {Scheme Procedure} set-tm:wday tm val
1252 Day of the week (0-6) with Sunday represented as 0.
1254 @deffn {Scheme Procedure} tm:yday tm
1255 @deffnx {Scheme Procedure} set-tm:yday tm val
1256 Day of the year (0-364, 365 in leap years).
1258 @deffn {Scheme Procedure} tm:isdst tm
1259 @deffnx {Scheme Procedure} set-tm:isdst tm val
1260 Daylight saving indicator (0 for ``no'', greater than 0 for ``yes'', less than
1263 @deffn {Scheme Procedure} tm:gmtoff tm
1264 @deffnx {Scheme Procedure} set-tm:gmtoff tm val
1265 Time zone offset in seconds west of @acronym{UTC} (-46800 to 43200).
1266 For example on East coast USA (zone @samp{EST+5}) this would be 18000
1267 (ie.@: @m{5\times60\times60,5*60*60}) in winter, or 14400
1268 (ie.@: @m{4\times60\times60,4*60*60}) during daylight savings.
1270 Note @code{tm:gmtoff} is not the same as @code{tm_gmtoff} in the C
1271 @code{tm} structure. @code{tm_gmtoff} is seconds east and hence the
1272 negative of the value here.
1274 @deffn {Scheme Procedure} tm:zone tm
1275 @deffnx {Scheme Procedure} set-tm:zone tm val
1276 Time zone label (a string), not necessarily unique.
1280 @deffn {Scheme Procedure} localtime time [zone]
1281 @deffnx {C Function} scm_localtime (time, zone)
1283 Return an object representing the broken down components of
1284 @var{time}, an integer like the one returned by
1285 @code{current-time}. The time zone for the calculation is
1286 optionally specified by @var{zone} (a string), otherwise the
1287 @env{TZ} environment variable or the system default is used.
1290 @deffn {Scheme Procedure} gmtime time
1291 @deffnx {C Function} scm_gmtime (time)
1292 Return an object representing the broken down components of
1293 @var{time}, an integer like the one returned by
1294 @code{current-time}. The values are calculated for @acronym{UTC}.
1297 @deffn {Scheme Procedure} mktime sbd-time [zone]
1298 @deffnx {C Function} scm_mktime (sbd_time, zone)
1299 For a broken down time object @var{sbd-time}, return a pair the
1300 @code{car} of which is an integer time like @code{current-time}, and
1301 the @code{cdr} of which is a new broken down time with normalized
1304 @var{zone} is a timezone string, or the default is the @env{TZ}
1305 environment variable or the system default (@pxref{TZ Variable,,
1306 Specifying the Time Zone with @env{TZ}, libc, GNU C Library Reference
1307 Manual}). @var{sbd-time} is taken to be in that @var{zone}.
1309 The following fields of @var{sbd-time} are used: @code{tm:year},
1310 @code{tm:mon}, @code{tm:mday}, @code{tm:hour}, @code{tm:min},
1311 @code{tm:sec}, @code{tm:isdst}. The values can be outside their usual
1312 ranges. For example @code{tm:hour} normally goes up to 23, but a
1313 value say 33 would mean 9 the following day.
1315 @code{tm:isdst} in @var{sbd-time} says whether the time given is with
1316 daylight savings or not. This is ignored if @var{zone} doesn't have
1317 any daylight savings adjustment amount.
1319 The broken down time in the return normalizes the values of
1320 @var{sbd-time} by bringing them into their usual ranges, and using the
1321 actual daylight savings rule for that time in @var{zone} (which may
1322 differ from what @var{sbd-time} had). The easiest way to think of
1323 this is that @var{sbd-time} plus @var{zone} converts to the integer
1324 UTC time, then a @code{localtime} is applied to get the normal
1325 presentation of that time, in @var{zone}.
1328 @deffn {Scheme Procedure} tzset
1329 @deffnx {C Function} scm_tzset ()
1330 Initialize the timezone from the @env{TZ} environment variable
1331 or the system default. It's not usually necessary to call this procedure
1332 since it's done automatically by other procedures that depend on the
1336 @deffn {Scheme Procedure} strftime format tm
1337 @deffnx {C Function} scm_strftime (format, tm)
1338 @cindex time formatting
1339 Return a string which is broken-down time structure @var{tm} formatted
1340 according to the given @var{format} string.
1342 @var{format} contains field specifications introduced by a @samp{%}
1343 character. See @ref{Formatting Calendar Time,,, libc, The GNU C
1344 Library Reference Manual}, or @samp{man 3 strftime}, for the available
1348 (strftime "%c" (localtime (current-time)))
1349 @result{} "Mon Mar 11 20:17:43 2002"
1352 If @code{setlocale} has been called (@pxref{Locales}), month and day
1353 names are from the current locale and in the locale character set.
1356 @deffn {Scheme Procedure} strptime format string
1357 @deffnx {C Function} scm_strptime (format, string)
1358 @cindex time parsing
1359 Performs the reverse action to @code{strftime}, parsing
1360 @var{string} according to the specification supplied in
1361 @var{format}. The interpretation of month and day names is
1362 dependent on the current locale. The value returned is a pair.
1363 The @acronym{CAR} has an object with time components
1364 in the form returned by @code{localtime} or @code{gmtime},
1365 but the time zone components
1366 are not usefully set.
1367 The @acronym{CDR} reports the number of characters from @var{string}
1368 which were used for the conversion.
1371 @defvar internal-time-units-per-second
1372 The value of this variable is the number of time units per second
1373 reported by the following procedures.
1376 @deffn {Scheme Procedure} times
1377 @deffnx {C Function} scm_times ()
1378 Return an object with information about real and processor
1379 time. The following procedures accept such an object as an
1380 argument and return a selected component:
1382 @deffn {Scheme Procedure} tms:clock tms
1383 The current real time, expressed as time units relative to an
1386 @deffn {Scheme Procedure} tms:utime tms
1387 The CPU time units used by the calling process.
1389 @deffn {Scheme Procedure} tms:stime tms
1390 The CPU time units used by the system on behalf of the calling
1393 @deffn {Scheme Procedure} tms:cutime tms
1394 The CPU time units used by terminated child processes of the
1395 calling process, whose status has been collected (e.g., using
1398 @deffn {Scheme Procedure} tms:cstime tms
1399 Similarly, the CPU times units used by the system on behalf of
1400 terminated child processes.
1404 @deffn {Scheme Procedure} get-internal-real-time
1405 @deffnx {C Function} scm_get_internal_real_time ()
1406 Return the number of time units since the interpreter was
1410 @deffn {Scheme Procedure} get-internal-run-time
1411 @deffnx {C Function} scm_get_internal_run_time ()
1412 Return the number of time units of processor time used by the
1413 interpreter. Both @emph{system} and @emph{user} time are
1414 included but subprocesses are not.
1417 @node Runtime Environment
1418 @subsection Runtime Environment
1420 @deffn {Scheme Procedure} program-arguments
1421 @deffnx {Scheme Procedure} command-line
1422 @deffnx {Scheme Procedure} set-program-arguments
1423 @deffnx {C Function} scm_program_arguments ()
1424 @deffnx {C Function} scm_set_program_arguments_scm (lst)
1425 @cindex command line
1426 @cindex program arguments
1427 Get the command line arguments passed to Guile, or set new arguments.
1429 The arguments are a list of strings, the first of which is the invoked
1430 program name. This is just @nicode{"guile"} (or the executable path)
1431 when run interactively, or it's the script name when running a script
1432 with @option{-s} (@pxref{Invoking Guile}).
1435 guile -L /my/extra/dir -s foo.scm abc def
1437 (program-arguments) @result{} ("foo.scm" "abc" "def")
1440 @code{set-program-arguments} allows a library module or similar to
1441 modify the arguments, for example to strip options it recognises,
1442 leaving the rest for the mainline.
1444 The argument list is held in a fluid, which means it's separate for
1445 each thread. Neither the list nor the strings within it are copied at
1446 any point and normally should not be mutated.
1448 The two names @code{program-arguments} and @code{command-line} are an
1449 historical accident, they both do exactly the same thing. The name
1450 @code{scm_set_program_arguments_scm} has an extra @code{_scm} on the
1451 end to avoid clashing with the C function below.
1454 @deftypefn {C Function} void scm_set_program_arguments (int argc, char **argv, char *first)
1455 @cindex command line
1456 @cindex program arguments
1457 Set the list of command line arguments for @code{program-arguments}
1458 and @code{command-line} above.
1460 @var{argv} is an array of null-terminated strings, as in a C
1461 @code{main} function. @var{argc} is the number of strings in
1462 @var{argv}, or if it's negative then a @code{NULL} in @var{argv} marks
1465 @var{first} is an extra string put at the start of the arguments, or
1466 @code{NULL} for no such extra. This is a convenient way to pass the
1467 program name after advancing @var{argv} to strip option arguments.
1472 char *progname = argv[0];
1473 for (argv++; argv[0] != NULL && argv[0][0] == '-'; argv++)
1475 /* munch option ... */
1477 /* remaining args for scheme level use */
1478 scm_set_program_arguments (-1, argv, progname);
1482 This sort of thing is often done at startup under
1483 @code{scm_boot_guile} with options handled at the C level removed.
1484 The given strings are all copied, so the C data is not accessed again
1485 once @code{scm_set_program_arguments} returns.
1488 @deffn {Scheme Procedure} getenv name
1489 @deffnx {C Function} scm_getenv (name)
1491 Looks up the string @var{name} in the current environment. The return
1492 value is @code{#f} unless a string of the form @code{NAME=VALUE} is
1493 found, in which case the string @code{VALUE} is returned.
1496 @deffn {Scheme Procedure} setenv name value
1497 Modifies the environment of the current process, which is
1498 also the default environment inherited by child processes.
1500 If @var{value} is @code{#f}, then @var{name} is removed from the
1501 environment. Otherwise, the string @var{name}=@var{value} is added
1502 to the environment, replacing any existing string with name matching
1505 The return value is unspecified.
1508 @deffn {Scheme Procedure} unsetenv name
1509 Remove variable @var{name} from the environment. The
1510 name can not contain a @samp{=} character.
1513 @deffn {Scheme Procedure} environ [env]
1514 @deffnx {C Function} scm_environ (env)
1515 If @var{env} is omitted, return the current environment (in the
1516 Unix sense) as a list of strings. Otherwise set the current
1517 environment, which is also the default environment for child
1518 processes, to the supplied list of strings. Each member of
1519 @var{env} should be of the form @var{name}=@var{value} and values of
1520 @var{name} should not be duplicated. If @var{env} is supplied
1521 then the return value is unspecified.
1524 @deffn {Scheme Procedure} putenv str
1525 @deffnx {C Function} scm_putenv (str)
1526 Modifies the environment of the current process, which is
1527 also the default environment inherited by child processes.
1529 If @var{str} is of the form @code{NAME=VALUE} then it will be written
1530 directly into the environment, replacing any existing environment string
1532 name matching @code{NAME}. If @var{str} does not contain an equal
1533 sign, then any existing string with name matching @var{str} will
1536 The return value is unspecified.
1541 @subsection Processes
1543 @cindex child processes
1546 @deffn {Scheme Procedure} chdir str
1547 @deffnx {C Function} scm_chdir (str)
1548 @cindex current directory
1549 Change the current working directory to @var{str}.
1550 The return value is unspecified.
1554 @deffn {Scheme Procedure} getcwd
1555 @deffnx {C Function} scm_getcwd ()
1556 Return the name of the current working directory.
1559 @deffn {Scheme Procedure} umask [mode]
1560 @deffnx {C Function} scm_umask (mode)
1561 If @var{mode} is omitted, returns a decimal number representing the
1562 current file creation mask. Otherwise the file creation mask is set
1563 to @var{mode} and the previous value is returned. @xref{Setting
1564 Permissions,,Assigning File Permissions,libc,The GNU C Library
1565 Reference Manual}, for more on how to use umasks.
1567 E.g., @code{(umask #o022)} sets the mask to octal 22/decimal 18.
1570 @deffn {Scheme Procedure} chroot path
1571 @deffnx {C Function} scm_chroot (path)
1572 Change the root directory to that specified in @var{path}.
1573 This directory will be used for path names beginning with
1574 @file{/}. The root directory is inherited by all children
1575 of the current process. Only the superuser may change the
1579 @deffn {Scheme Procedure} getpid
1580 @deffnx {C Function} scm_getpid ()
1581 Return an integer representing the current process ID.
1584 @deffn {Scheme Procedure} getgroups
1585 @deffnx {C Function} scm_getgroups ()
1586 Return a vector of integers representing the current
1587 supplementary group IDs.
1590 @deffn {Scheme Procedure} getppid
1591 @deffnx {C Function} scm_getppid ()
1592 Return an integer representing the process ID of the parent
1596 @deffn {Scheme Procedure} getuid
1597 @deffnx {C Function} scm_getuid ()
1598 Return an integer representing the current real user ID.
1601 @deffn {Scheme Procedure} getgid
1602 @deffnx {C Function} scm_getgid ()
1603 Return an integer representing the current real group ID.
1606 @deffn {Scheme Procedure} geteuid
1607 @deffnx {C Function} scm_geteuid ()
1608 Return an integer representing the current effective user ID.
1609 If the system does not support effective IDs, then the real ID
1610 is returned. @code{(provided? 'EIDs)} reports whether the
1611 system supports effective IDs.
1614 @deffn {Scheme Procedure} getegid
1615 @deffnx {C Function} scm_getegid ()
1616 Return an integer representing the current effective group ID.
1617 If the system does not support effective IDs, then the real ID
1618 is returned. @code{(provided? 'EIDs)} reports whether the
1619 system supports effective IDs.
1622 @deffn {Scheme Procedure} setgroups vec
1623 @deffnx {C Function} scm_setgroups (vec)
1624 Set the current set of supplementary group IDs to the integers in the
1625 given vector @var{vec}. The return value is unspecified.
1627 Generally only the superuser can set the process group IDs
1628 (@pxref{Setting Groups, Setting the Group IDs,, libc, The GNU C
1629 Library Reference Manual}).
1632 @deffn {Scheme Procedure} setuid id
1633 @deffnx {C Function} scm_setuid (id)
1634 Sets both the real and effective user IDs to the integer @var{id}, provided
1635 the process has appropriate privileges.
1636 The return value is unspecified.
1639 @deffn {Scheme Procedure} setgid id
1640 @deffnx {C Function} scm_setgid (id)
1641 Sets both the real and effective group IDs to the integer @var{id}, provided
1642 the process has appropriate privileges.
1643 The return value is unspecified.
1646 @deffn {Scheme Procedure} seteuid id
1647 @deffnx {C Function} scm_seteuid (id)
1648 Sets the effective user ID to the integer @var{id}, provided the process
1649 has appropriate privileges. If effective IDs are not supported, the
1650 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1651 system supports effective IDs.
1652 The return value is unspecified.
1655 @deffn {Scheme Procedure} setegid id
1656 @deffnx {C Function} scm_setegid (id)
1657 Sets the effective group ID to the integer @var{id}, provided the process
1658 has appropriate privileges. If effective IDs are not supported, the
1659 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1660 system supports effective IDs.
1661 The return value is unspecified.
1664 @deffn {Scheme Procedure} getpgrp
1665 @deffnx {C Function} scm_getpgrp ()
1666 Return an integer representing the current process group ID.
1667 This is the @acronym{POSIX} definition, not @acronym{BSD}.
1670 @deffn {Scheme Procedure} setpgid pid pgid
1671 @deffnx {C Function} scm_setpgid (pid, pgid)
1672 Move the process @var{pid} into the process group @var{pgid}. @var{pid} or
1673 @var{pgid} must be integers: they can be zero to indicate the ID of the
1675 Fails on systems that do not support job control.
1676 The return value is unspecified.
1679 @deffn {Scheme Procedure} setsid
1680 @deffnx {C Function} scm_setsid ()
1681 Creates a new session. The current process becomes the session leader
1682 and is put in a new process group. The process will be detached
1683 from its controlling terminal if it has one.
1684 The return value is an integer representing the new process group ID.
1687 @deffn {Scheme Procedure} getsid pid
1688 @deffnx {C Function} scm_getsid (pid)
1689 Returns the session ID of process @var{pid}. (The session
1690 ID of a process is the process group ID of its session leader.)
1693 @deffn {Scheme Procedure} waitpid pid [options]
1694 @deffnx {C Function} scm_waitpid (pid, options)
1695 This procedure collects status information from a child process which
1696 has terminated or (optionally) stopped. Normally it will
1697 suspend the calling process until this can be done. If more than one
1698 child process is eligible then one will be chosen by the operating system.
1700 The value of @var{pid} determines the behaviour:
1703 @item @var{pid} greater than 0
1704 Request status information from the specified child process.
1705 @item @var{pid} equal to -1 or @code{WAIT_ANY}
1707 Request status information for any child process.
1708 @item @var{pid} equal to 0 or @code{WAIT_MYPGRP}
1710 Request status information for any child process in the current process
1712 @item @var{pid} less than -1
1713 Request status information for any child process whose process group ID
1714 is @minus{}@var{pid}.
1717 The @var{options} argument, if supplied, should be the bitwise OR of the
1718 values of zero or more of the following variables:
1721 Return immediately even if there are no child processes to be collected.
1725 Report status information for stopped processes as well as terminated
1729 The return value is a pair containing:
1733 The process ID of the child process, or 0 if @code{WNOHANG} was
1734 specified and no process was collected.
1736 The integer status value.
1741 functions can be used to decode the process status code returned
1744 @deffn {Scheme Procedure} status:exit-val status
1745 @deffnx {C Function} scm_status_exit_val (status)
1746 Return the exit status value, as would be set if a process
1747 ended normally through a call to @code{exit} or @code{_exit},
1748 if any, otherwise @code{#f}.
1751 @deffn {Scheme Procedure} status:term-sig status
1752 @deffnx {C Function} scm_status_term_sig (status)
1753 Return the signal number which terminated the process, if any,
1754 otherwise @code{#f}.
1757 @deffn {Scheme Procedure} status:stop-sig status
1758 @deffnx {C Function} scm_status_stop_sig (status)
1759 Return the signal number which stopped the process, if any,
1760 otherwise @code{#f}.
1763 @deffn {Scheme Procedure} system [cmd]
1764 @deffnx {C Function} scm_system (cmd)
1765 Execute @var{cmd} using the operating system's ``command
1766 processor''. Under Unix this is usually the default shell
1767 @code{sh}. The value returned is @var{cmd}'s exit status as
1768 returned by @code{waitpid}, which can be interpreted using the
1771 If @code{system} is called without arguments, return a boolean
1772 indicating whether the command processor is available.
1775 @deffn {Scheme Procedure} system* arg1 arg2 @dots{}
1776 @deffnx {C Function} scm_system_star (args)
1777 Execute the command indicated by @var{arg1} @var{arg2} @enddots{}. The
1778 first element must be a string indicating the command to be executed,
1779 and the remaining items must be strings representing each of the
1780 arguments to that command.
1782 This function returns the exit status of the command as provided by
1783 @code{waitpid}. This value can be handled with @code{status:exit-val}
1784 and the related functions.
1786 @code{system*} is similar to @code{system}, but accepts only one
1787 string per-argument, and performs no shell interpretation. The
1788 command is executed using fork and execlp. Accordingly this function
1789 may be safer than @code{system} in situations where shell
1790 interpretation is not required.
1792 Example: (system* "echo" "foo" "bar")
1795 @deffn {Scheme Procedure} quit [status]
1796 @deffnx {Scheme Procedure} exit [status]
1797 Terminate the current process with proper unwinding of the Scheme stack.
1798 The exit status zero if @var{status} is not supplied. If @var{status}
1799 is supplied, and it is an integer, that integer is used as the exit
1800 status. If @var{status} is @code{#t} or @code{#f}, the exit status is
1801 @var{EXIT_SUCCESS} or @var{EXIT_FAILURE}, respectively.
1803 The procedure @code{exit} is an alias of @code{quit}. They have the
1807 @defvr {Scheme Variable} EXIT_SUCCESS
1808 @defvrx {Scheme Variable} EXIT_FAILURE
1809 These constants represent the standard exit codes for success (zero) or
1813 @deffn {Scheme Procedure} primitive-exit [status]
1814 @deffnx {Scheme Procedure} primitive-_exit [status]
1815 @deffnx {C Function} scm_primitive_exit (status)
1816 @deffnx {C Function} scm_primitive__exit (status)
1817 Terminate the current process without unwinding the Scheme stack. The
1818 exit status is @var{status} if supplied, otherwise zero.
1820 @code{primitive-exit} uses the C @code{exit} function and hence runs
1821 usual C level cleanups (flush output streams, call @code{atexit}
1822 functions, etc, see @ref{Normal Termination,,, libc, The GNU C Library
1823 Reference Manual})).
1825 @code{primitive-_exit} is the @code{_exit} system call
1826 (@pxref{Termination Internals,,, libc, The GNU C Library Reference
1827 Manual}). This terminates the program immediately, with neither
1828 Scheme-level nor C-level cleanups.
1830 The typical use for @code{primitive-_exit} is from a child process
1831 created with @code{primitive-fork}. For example in a Gdk program the
1832 child process inherits the X server connection and a C-level
1833 @code{atexit} cleanup which will close that connection. But closing
1834 in the child would upset the protocol in the parent, so
1835 @code{primitive-_exit} should be used to exit without that.
1838 @deffn {Scheme Procedure} execl filename arg @dots{}
1839 @deffnx {C Function} scm_execl (filename, args)
1840 Executes the file named by @var{filename} as a new process image.
1841 The remaining arguments are supplied to the process; from a C program
1842 they are accessible as the @code{argv} argument to @code{main}.
1843 Conventionally the first @var{arg} is the same as @var{filename}.
1844 All arguments must be strings.
1846 If @var{arg} is missing, @var{filename} is executed with a null
1847 argument list, which may have system-dependent side-effects.
1849 This procedure is currently implemented using the @code{execv} system
1850 call, but we call it @code{execl} because of its Scheme calling interface.
1853 @deffn {Scheme Procedure} execlp filename arg @dots{}
1854 @deffnx {C Function} scm_execlp (filename, args)
1855 Similar to @code{execl}, however if
1856 @var{filename} does not contain a slash
1857 then the file to execute will be located by searching the
1858 directories listed in the @code{PATH} environment variable.
1860 This procedure is currently implemented using the @code{execvp} system
1861 call, but we call it @code{execlp} because of its Scheme calling interface.
1864 @deffn {Scheme Procedure} execle filename env arg @dots{}
1865 @deffnx {C Function} scm_execle (filename, env, args)
1866 Similar to @code{execl}, but the environment of the new process is
1867 specified by @var{env}, which must be a list of strings as returned by the
1868 @code{environ} procedure.
1870 This procedure is currently implemented using the @code{execve} system
1871 call, but we call it @code{execle} because of its Scheme calling interface.
1874 @deffn {Scheme Procedure} primitive-fork
1875 @deffnx {C Function} scm_fork ()
1876 Creates a new ``child'' process by duplicating the current ``parent'' process.
1877 In the child the return value is 0. In the parent the return value is
1878 the integer process ID of the child.
1880 Note that it is unsafe to fork a process that has multiple threads
1881 running, as only the thread that calls @code{primitive-fork} will
1882 persist in the child. Any resources that other threads held, such as
1883 locked mutexes or open file descriptors, are lost. Indeed,
1884 @acronym{POSIX} specifies that only async-signal-safe procedures are
1885 safe to call after a multithreaded fork, which is a very limited set.
1886 Guile issues a warning if it detects a fork from a multi-threaded
1889 If you are going to @code{exec} soon after forking, the procedures in
1890 @code{(ice-9 popen)} may be useful to you, as they fork and exec within
1891 an async-signal-safe function carefully written to ensure robust program
1892 behavior, even in the presence of threads. @xref{Pipes}, for more.
1894 This procedure has been renamed from @code{fork} to avoid a naming conflict
1898 @deffn {Scheme Procedure} nice incr
1899 @deffnx {C Function} scm_nice (incr)
1900 @cindex process priority
1901 Increment the priority of the current process by @var{incr}. A higher
1902 priority value means that the process runs less often.
1903 The return value is unspecified.
1906 @deffn {Scheme Procedure} setpriority which who prio
1907 @deffnx {C Function} scm_setpriority (which, who, prio)
1908 @vindex PRIO_PROCESS
1911 Set the scheduling priority of the process, process group
1912 or user, as indicated by @var{which} and @var{who}. @var{which}
1913 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1914 or @code{PRIO_USER}, and @var{who} is interpreted relative to
1915 @var{which} (a process identifier for @code{PRIO_PROCESS},
1916 process group identifier for @code{PRIO_PGRP}, and a user
1917 identifier for @code{PRIO_USER}. A zero value of @var{who}
1918 denotes the current process, process group, or user.
1919 @var{prio} is a value in the range [@minus{}20,20]. The default
1920 priority is 0; lower priorities (in numerical terms) cause more
1921 favorable scheduling. Sets the priority of all of the specified
1922 processes. Only the super-user may lower priorities. The return
1923 value is not specified.
1926 @deffn {Scheme Procedure} getpriority which who
1927 @deffnx {C Function} scm_getpriority (which, who)
1928 @vindex PRIO_PROCESS
1931 Return the scheduling priority of the process, process group
1932 or user, as indicated by @var{which} and @var{who}. @var{which}
1933 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1934 or @code{PRIO_USER}, and @var{who} should be interpreted depending on
1935 @var{which} (a process identifier for @code{PRIO_PROCESS},
1936 process group identifier for @code{PRIO_PGRP}, and a user
1937 identifier for @code{PRIO_USER}). A zero value of @var{who}
1938 denotes the current process, process group, or user. Return
1939 the highest priority (lowest numerical value) of any of the
1940 specified processes.
1943 @cindex affinity, CPU
1945 @deffn {Scheme Procedure} getaffinity pid
1946 @deffnx {C Function} scm_getaffinity (pid)
1947 Return a bitvector representing the CPU affinity mask for
1948 process @var{pid}. Each CPU the process has affinity with
1949 has its corresponding bit set in the returned bitvector.
1950 The number of bits set is a good estimate of how many CPUs
1951 Guile can use without stepping on other processes' toes.
1953 Currently this procedure is only defined on GNU variants
1954 (@pxref{CPU Affinity, @code{sched_getaffinity},, libc, The
1955 GNU C Library Reference Manual}).
1958 @deffn {Scheme Procedure} setaffinity pid mask
1959 @deffnx {C Function} scm_setaffinity (pid, mask)
1960 Install the CPU affinity mask @var{mask}, a bitvector, for
1961 the process or thread with ID @var{pid}. The return value
1964 Currently this procedure is only defined on GNU variants
1965 (@pxref{CPU Affinity, @code{sched_setaffinity},, libc, The
1966 GNU C Library Reference Manual}).
1969 @deffn {Scheme Procedure} total-processor-count
1970 @deffnx {C Function} scm_total_processor_count ()
1971 Return the total number of processors of the machine, which
1972 is guaranteed to be at least 1. A ``processor'' here is a
1973 thread execution unit, which can be either:
1976 @item an execution core in a (possibly multi-core) chip, in a
1977 (possibly multi- chip) module, in a single computer, or
1978 @item a thread execution unit inside a core in the case of
1979 @dfn{hyper-threaded} CPUs.
1982 Which of the two definitions is used, is unspecified.
1985 @deffn {Scheme Procedure} current-processor-count
1986 @deffnx {C Function} scm_current_processor_count ()
1987 Like @code{total-processor-count}, but return the number of
1988 processors available to the current process. See
1989 @code{setaffinity} and @code{getaffinity} for more
1998 The following procedures raise, handle and wait for signals.
2000 Scheme code signal handlers are run via a system async (@pxref{System
2001 asyncs}), so they're called in the handler's thread at the next safe
2002 opportunity. Generally this is after any currently executing
2003 primitive procedure finishes (which could be a long time for
2004 primitives that wait for an external event).
2006 @deffn {Scheme Procedure} kill pid sig
2007 @deffnx {C Function} scm_kill (pid, sig)
2008 Sends a signal to the specified process or group of processes.
2010 @var{pid} specifies the processes to which the signal is sent:
2013 @item @var{pid} greater than 0
2014 The process whose identifier is @var{pid}.
2015 @item @var{pid} equal to 0
2016 All processes in the current process group.
2017 @item @var{pid} less than -1
2018 The process group whose identifier is -@var{pid}
2019 @item @var{pid} equal to -1
2020 If the process is privileged, all processes except for some special
2021 system processes. Otherwise, all processes with the current effective
2025 @var{sig} should be specified using a variable corresponding to
2026 the Unix symbolic name, e.g.,
2036 A full list of signals on the GNU system may be found in @ref{Standard
2037 Signals,,,libc,The GNU C Library Reference Manual}.
2040 @deffn {Scheme Procedure} raise sig
2041 @deffnx {C Function} scm_raise (sig)
2042 Sends a specified signal @var{sig} to the current process, where
2043 @var{sig} is as described for the @code{kill} procedure.
2046 @deffn {Scheme Procedure} sigaction signum [handler [flags [thread]]]
2047 @deffnx {C Function} scm_sigaction (signum, handler, flags)
2048 @deffnx {C Function} scm_sigaction_for_thread (signum, handler, flags, thread)
2049 Install or report the signal handler for a specified signal.
2051 @var{signum} is the signal number, which can be specified using the value
2052 of variables such as @code{SIGINT}.
2054 If @var{handler} is omitted, @code{sigaction} returns a pair: the
2055 @acronym{CAR} is the current signal hander, which will be either an
2056 integer with the value @code{SIG_DFL} (default action) or
2057 @code{SIG_IGN} (ignore), or the Scheme procedure which handles the
2058 signal, or @code{#f} if a non-Scheme procedure handles the signal.
2059 The @acronym{CDR} contains the current @code{sigaction} flags for the
2062 If @var{handler} is provided, it is installed as the new handler for
2063 @var{signum}. @var{handler} can be a Scheme procedure taking one
2064 argument, or the value of @code{SIG_DFL} (default action) or
2065 @code{SIG_IGN} (ignore), or @code{#f} to restore whatever signal handler
2066 was installed before @code{sigaction} was first used. When a scheme
2067 procedure has been specified, that procedure will run in the given
2068 @var{thread}. When no thread has been given, the thread that made this
2069 call to @code{sigaction} is used.
2071 @var{flags} is a @code{logior} (@pxref{Bitwise Operations}) of the
2072 following (where provided by the system), or @code{0} for none.
2074 @defvar SA_NOCLDSTOP
2075 By default, @code{SIGCHLD} is signalled when a child process stops
2076 (ie.@: receives @code{SIGSTOP}), and when a child process terminates.
2077 With the @code{SA_NOCLDSTOP} flag, @code{SIGCHLD} is only signalled
2078 for termination, not stopping.
2080 @code{SA_NOCLDSTOP} has no effect on signals other than
2085 If a signal occurs while in a system call, deliver the signal then
2086 restart the system call (as opposed to returning an @code{EINTR} error
2090 The return value is a pair with information about the old handler as
2093 This interface does not provide access to the ``signal blocking''
2094 facility. Maybe this is not needed, since the thread support may
2095 provide solutions to the problem of consistent access to data
2099 @deffn {Scheme Procedure} restore-signals
2100 @deffnx {C Function} scm_restore_signals ()
2101 Return all signal handlers to the values they had before any call to
2102 @code{sigaction} was made. The return value is unspecified.
2105 @deffn {Scheme Procedure} alarm i
2106 @deffnx {C Function} scm_alarm (i)
2107 Set a timer to raise a @code{SIGALRM} signal after the specified
2108 number of seconds (an integer). It's advisable to install a signal
2110 @code{SIGALRM} beforehand, since the default action is to terminate
2113 The return value indicates the time remaining for the previous alarm,
2114 if any. The new value replaces the previous alarm. If there was
2115 no previous alarm, the return value is zero.
2118 @deffn {Scheme Procedure} pause
2119 @deffnx {C Function} scm_pause ()
2120 Pause the current process (thread?) until a signal arrives whose
2121 action is to either terminate the current process or invoke a
2122 handler procedure. The return value is unspecified.
2125 @deffn {Scheme Procedure} sleep secs
2126 @deffnx {Scheme Procedure} usleep usecs
2127 @deffnx {C Function} scm_sleep (secs)
2128 @deffnx {C Function} scm_usleep (usecs)
2129 Wait the given period @var{secs} seconds or @var{usecs} microseconds
2130 (both integers). If a signal arrives the wait stops and the return
2131 value is the time remaining, in seconds or microseconds respectively.
2132 If the period elapses with no signal the return is zero.
2134 On most systems the process scheduler is not microsecond accurate and
2135 the actual period slept by @code{usleep} might be rounded to a system
2136 clock tick boundary, which might be 10 milliseconds for instance.
2138 See @code{scm_std_sleep} and @code{scm_std_usleep} for equivalents at
2139 the C level (@pxref{Blocking}).
2142 @deffn {Scheme Procedure} getitimer which_timer
2143 @deffnx {Scheme Procedure} setitimer which_timer interval_seconds interval_microseconds value_seconds value_microseconds
2144 @deffnx {C Function} scm_getitimer (which_timer)
2145 @deffnx {C Function} scm_setitimer (which_timer, interval_seconds, interval_microseconds, value_seconds, value_microseconds)
2146 Get or set the periods programmed in certain system timers.
2148 These timers have two settings. The first setting, the interval, is the
2149 value at which the timer will be reset when the current timer expires.
2150 The second is the current value of the timer, indicating when the next
2151 expiry will be signalled.
2153 @var{which_timer} is one of the following values:
2156 A real-time timer, counting down elapsed real time. At zero it raises
2157 @code{SIGALRM}. This is like @code{alarm} above, but with a higher
2161 @defvar ITIMER_VIRTUAL
2162 A virtual-time timer, counting down while the current process is
2163 actually using CPU. At zero it raises @code{SIGVTALRM}.
2167 A profiling timer, counting down while the process is running (like
2168 @code{ITIMER_VIRTUAL}) and also while system calls are running on the
2169 process's behalf. At zero it raises a @code{SIGPROF}.
2171 This timer is intended for profiling where a program is spending its
2172 time (by looking where it is when the timer goes off).
2175 @code{getitimer} returns the restart timer value and its current value,
2176 as a list containing two pairs. Each pair is a time in seconds and
2177 microseconds: @code{((@var{interval_secs} . @var{interval_usecs})
2178 (@var{value_secs} . @var{value_usecs}))}.
2180 @code{setitimer} sets the timer values similarly, in seconds and
2181 microseconds (which must be integers). The interval value can be zero
2182 to have the timer run down just once. The return value is the timer's
2183 previous setting, in the same form as @code{getitimer} returns.
2186 (setitimer ITIMER_REAL
2187 5 500000 ;; Raise SIGALRM every 5.5 seconds
2188 2 0) ;; with the first SIGALRM in 2 seconds
2191 Although the timers are programmed in microseconds, the actual
2192 accuracy might not be that high.
2196 @node Terminals and Ptys
2197 @subsection Terminals and Ptys
2199 @deffn {Scheme Procedure} isatty? port
2200 @deffnx {C Function} scm_isatty_p (port)
2202 Return @code{#t} if @var{port} is using a serial non--file
2203 device, otherwise @code{#f}.
2206 @deffn {Scheme Procedure} ttyname port
2207 @deffnx {C Function} scm_ttyname (port)
2209 Return a string with the name of the serial terminal device
2210 underlying @var{port}.
2213 @deffn {Scheme Procedure} ctermid
2214 @deffnx {C Function} scm_ctermid ()
2216 Return a string containing the file name of the controlling
2217 terminal for the current process.
2220 @deffn {Scheme Procedure} tcgetpgrp port
2221 @deffnx {C Function} scm_tcgetpgrp (port)
2222 @cindex process group
2223 Return the process group ID of the foreground process group
2224 associated with the terminal open on the file descriptor
2225 underlying @var{port}.
2227 If there is no foreground process group, the return value is a
2228 number greater than 1 that does not match the process group ID
2229 of any existing process group. This can happen if all of the
2230 processes in the job that was formerly the foreground job have
2231 terminated, and no other job has yet been moved into the
2235 @deffn {Scheme Procedure} tcsetpgrp port pgid
2236 @deffnx {C Function} scm_tcsetpgrp (port, pgid)
2237 @cindex process group
2238 Set the foreground process group ID for the terminal used by the file
2239 descriptor underlying @var{port} to the integer @var{pgid}.
2241 must be a member of the same session as @var{pgid} and must have the same
2242 controlling terminal. The return value is unspecified.
2249 The following procedures are similar to the @code{popen} and
2250 @code{pclose} system routines. The code is in a separate ``popen''
2251 module@footnote{This module is only available on systems where the
2252 @code{fork} feature is provided (@pxref{Common Feature Symbols}).}:
2255 (use-modules (ice-9 popen))
2259 @deffn {Scheme Procedure} open-pipe command mode
2260 @deffnx {Scheme Procedure} open-pipe* mode prog [args...]
2261 Execute a command in a subprocess, with a pipe to it or from it, or
2262 with pipes in both directions.
2264 @code{open-pipe} runs the shell @var{command} using @samp{/bin/sh -c}.
2265 @code{open-pipe*} executes @var{prog} directly, with the optional
2266 @var{args} arguments (all strings).
2268 @var{mode} should be one of the following values. @code{OPEN_READ} is
2269 an input pipe, ie.@: to read from the subprocess. @code{OPEN_WRITE}
2270 is an output pipe, ie.@: to write to it.
2277 For an input pipe, the child's standard output is the pipe and
2278 standard input is inherited from @code{current-input-port}. For an
2279 output pipe, the child's standard input is the pipe and standard
2280 output is inherited from @code{current-output-port}. In all cases
2281 cases the child's standard error is inherited from
2282 @code{current-error-port} (@pxref{Default Ports}).
2284 If those @code{current-X-ports} are not files of some kind, and hence
2285 don't have file descriptors for the child, then @file{/dev/null} is
2288 Care should be taken with @code{OPEN_BOTH}, a deadlock will occur if
2289 both parent and child are writing, and waiting until the write
2290 completes before doing any reading. Each direction has
2291 @code{PIPE_BUF} bytes of buffering (@pxref{Ports and File
2292 Descriptors}), which will be enough for small writes, but not for say
2293 putting a big file through a filter.
2296 @deffn {Scheme Procedure} open-input-pipe command
2297 Equivalent to @code{open-pipe} with mode @code{OPEN_READ}.
2300 (let* ((port (open-input-pipe "date --utc"))
2301 (str (read-line port)))
2304 @result{} "Mon Mar 11 20:10:44 UTC 2002"
2308 @deffn {Scheme Procedure} open-output-pipe command
2309 Equivalent to @code{open-pipe} with mode @code{OPEN_WRITE}.
2312 (let ((port (open-output-pipe "lpr")))
2313 (display "Something for the line printer.\n" port)
2314 (if (not (eqv? 0 (status:exit-val (close-pipe port))))
2315 (error "Cannot print")))
2319 @deffn {Scheme Procedure} open-input-output-pipe command
2320 Equivalent to @code{open-pipe} with mode @code{OPEN_BOTH}.
2324 @deffn {Scheme Procedure} close-pipe port
2325 Close a pipe created by @code{open-pipe}, wait for the process to
2326 terminate, and return the wait status code. The status is as per
2327 @code{waitpid} and can be decoded with @code{status:exit-val} etc
2332 @code{waitpid WAIT_ANY} should not be used when pipes are open, since
2333 it can reap a pipe's child process, causing an error from a subsequent
2336 @code{close-port} (@pxref{Closing}) can close a pipe, but it doesn't
2337 reap the child process.
2339 The garbage collector will close a pipe no longer in use, and reap the
2340 child process with @code{waitpid}. If the child hasn't yet terminated
2341 the garbage collector doesn't block, but instead checks again in the
2344 Many systems have per-user and system-wide limits on the number of
2345 processes, and a system-wide limit on the number of pipes, so pipes
2346 should be closed explicitly when no longer needed, rather than letting
2347 the garbage collector pick them up at some later time.
2351 @subsection Networking
2355 * Network Address Conversion::
2356 * Network Databases::
2357 * Network Socket Address::
2358 * Network Sockets and Communication::
2359 * Internet Socket Examples::
2362 @node Network Address Conversion
2363 @subsubsection Network Address Conversion
2364 @cindex network address
2366 This section describes procedures which convert internet addresses
2367 between numeric and string formats.
2369 @subsubheading IPv4 Address Conversion
2372 An IPv4 Internet address is a 4-byte value, represented in Guile as an
2373 integer in host byte order, so that say ``0.0.0.1'' is 1, or
2374 ``1.0.0.0'' is 16777216.
2376 Some underlying C functions use network byte order for addresses,
2377 Guile converts as necessary so that at the Scheme level its host byte
2381 For a server, this can be used with @code{bind} (@pxref{Network
2382 Sockets and Communication}) to allow connections from any interface on
2386 @defvar INADDR_BROADCAST
2387 The broadcast address on the local network.
2390 @defvar INADDR_LOOPBACK
2391 The address of the local host using the loopback device, ie.@:
2395 @c INADDR_NONE is defined in the code, but serves no purpose.
2396 @c inet_addr() returns it as an error indication, but that function
2397 @c isn't provided, for the good reason that inet_aton() does the same
2398 @c job and gives an unambiguous error indication. (INADDR_NONE is a
2399 @c valid 4-byte value, in glibc it's the same as INADDR_BROADCAST.)
2401 @c @defvar INADDR_NONE
2405 @deffn {Scheme Procedure} inet-aton address
2406 @deffnx {C Function} scm_inet_aton (address)
2407 This function is deprecated in favor of @code{inet-pton}.
2409 Convert an IPv4 Internet address from printable string
2410 (dotted decimal notation) to an integer. E.g.,
2413 (inet-aton "127.0.0.1") @result{} 2130706433
2417 @deffn {Scheme Procedure} inet-ntoa inetid
2418 @deffnx {C Function} scm_inet_ntoa (inetid)
2419 This function is deprecated in favor of @code{inet-ntop}.
2421 Convert an IPv4 Internet address to a printable
2422 (dotted decimal notation) string. E.g.,
2425 (inet-ntoa 2130706433) @result{} "127.0.0.1"
2429 @deffn {Scheme Procedure} inet-netof address
2430 @deffnx {C Function} scm_inet_netof (address)
2431 Return the network number part of the given IPv4
2432 Internet address. E.g.,
2435 (inet-netof 2130706433) @result{} 127
2439 @deffn {Scheme Procedure} inet-lnaof address
2440 @deffnx {C Function} scm_lnaof (address)
2441 Return the local-address-with-network part of the given
2442 IPv4 Internet address, using the obsolete class A/B/C system.
2446 (inet-lnaof 2130706433) @result{} 1
2450 @deffn {Scheme Procedure} inet-makeaddr net lna
2451 @deffnx {C Function} scm_inet_makeaddr (net, lna)
2452 Make an IPv4 Internet address by combining the network number
2453 @var{net} with the local-address-within-network number
2457 (inet-makeaddr 127 1) @result{} 2130706433
2461 @subsubheading IPv6 Address Conversion
2464 An IPv6 Internet address is a 16-byte value, represented in Guile as
2465 an integer in host byte order, so that say ``::1'' is 1.
2467 @deffn {Scheme Procedure} inet-ntop family address
2468 @deffnx {C Function} scm_inet_ntop (family, address)
2469 Convert a network address from an integer to a printable string.
2470 @var{family} can be @code{AF_INET} or @code{AF_INET6}. E.g.,
2473 (inet-ntop AF_INET 2130706433) @result{} "127.0.0.1"
2474 (inet-ntop AF_INET6 (- (expt 2 128) 1))
2475 @result{} "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff"
2479 @deffn {Scheme Procedure} inet-pton family address
2480 @deffnx {C Function} scm_inet_pton (family, address)
2481 Convert a string containing a printable network address to an integer
2482 address. @var{family} can be @code{AF_INET} or @code{AF_INET6}.
2486 (inet-pton AF_INET "127.0.0.1") @result{} 2130706433
2487 (inet-pton AF_INET6 "::1") @result{} 1
2492 @node Network Databases
2493 @subsubsection Network Databases
2494 @cindex network database
2496 This section describes procedures which query various network databases.
2497 Care should be taken when using the database routines since they are not
2500 @subsubheading @code{getaddrinfo}
2502 @cindex @code{addrinfo} object type
2503 @cindex host name lookup
2504 @cindex service name lookup
2506 The @code{getaddrinfo} procedure maps host and service names to socket addresses
2507 and associated information in a protocol-independent way.
2509 @deffn {Scheme Procedure} getaddrinfo name service [hint_flags [hint_family [hint_socktype [hint_protocol]]]]
2510 @deffnx {C Function} scm_getaddrinfo (name, service, hint_flags, hint_family, hint_socktype, hint_protocol)
2511 Return a list of @code{addrinfo} structures containing
2512 a socket address and associated information for host @var{name}
2513 and/or @var{service} to be used in creating a socket with
2514 which to address the specified service.
2517 (let* ((ai (car (getaddrinfo "www.gnu.org" "http")))
2518 (s (socket (addrinfo:fam ai) (addrinfo:socktype ai)
2519 (addrinfo:protocol ai))))
2520 (connect s (addrinfo:addr ai))
2524 When @var{service} is omitted or is @code{#f}, return
2525 network-level addresses for @var{name}. When @var{name}
2526 is @code{#f} @var{service} must be provided and service
2527 locations local to the caller are returned.
2529 Additional hints can be provided. When specified,
2530 @var{hint_flags} should be a bitwise-or of zero or more
2531 constants among the following:
2535 Socket address is intended for @code{bind}.
2538 Request for canonical host name, available via
2539 @code{addrinfo:canonname}. This makes sense mainly when
2540 DNS lookups are involved.
2542 @item AI_NUMERICHOST
2543 Specifies that @var{name} is a numeric host address string
2544 (e.g., @code{"127.0.0.1"}), meaning that name resolution
2547 @item AI_NUMERICSERV
2548 Likewise, specifies that @var{service} is a numeric port
2549 string (e.g., @code{"80"}).
2552 Return only addresses configured on the local system It is
2553 highly recommended to provide this flag when the returned
2554 socket addresses are to be used to make connections;
2555 otherwise, some of the returned addresses could be unreachable
2556 or use a protocol that is not supported.
2559 When looking up IPv6 addresses, return mapped IPv4 addresses if
2560 there is no IPv6 address available at all.
2563 If this flag is set along with @code{AI_V4MAPPED} when looking up IPv6
2564 addresses, return all IPv6 addresses as well as all IPv4 addresses, the latter
2565 mapped to IPv6 format.
2568 When given, @var{hint_family} should specify the requested
2569 address family, e.g., @code{AF_INET6}. Similarly,
2570 @var{hint_socktype} should specify the requested socket type
2571 (e.g., @code{SOCK_DGRAM}), and @var{hint_protocol} should
2572 specify the requested protocol (its value is interpreted
2573 as in calls to @code{socket}).
2575 On error, an exception with key @code{getaddrinfo-error} is
2576 thrown, with an error code (an integer) as its argument:
2579 (catch 'getaddrinfo-error
2581 (getaddrinfo "www.gnu.org" "gopher"))
2582 (lambda (key errcode)
2583 (cond ((= errcode EAI_SERVICE)
2584 (display "doesn't know about Gopher!\n"))
2585 ((= errcode EAI_NONAME)
2586 (display "www.gnu.org not found\\n"))
2588 (format #t "something wrong: ~a\n"
2589 (gai-strerror errcode))))))
2596 The name or service could not be resolved at this time. Future
2597 attempts may succeed.
2600 @var{hint_flags} contains an invalid value.
2603 A non-recoverable error occurred when attempting to
2607 @var{hint_family} was not recognized.
2610 Either @var{name} does not resolve for the supplied parameters,
2611 or neither @var{name} nor @var{service} were supplied.
2614 This non-POSIX error code can be returned on some systems (GNU
2615 and Darwin, at least), for example when @var{name} is known
2616 but requests that were made turned out no data. Error handling
2617 code should be prepared to handle it when it is defined.
2620 @var{service} was not recognized for the specified socket type.
2623 @var{hint_socktype} was not recognized.
2626 A system error occurred. In C, the error code can be found in
2627 @code{errno}; this value is not accessible from Scheme, but in
2628 practice it provides little information about the actual error
2630 @c See <http://bugs.gnu.org/13958>.
2633 Users are encouraged to read the
2634 @url{http://www.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html,
2635 "POSIX specification} for more details.
2638 The following procedures take an @code{addrinfo} object as returned by
2641 @deffn {Scheme Procedure} addrinfo:flags ai
2642 Return flags for @var{ai} as a bitwise or of @code{AI_} values (see above).
2645 @deffn {Scheme Procedure} addrinfo:fam ai
2646 Return the address family of @var{ai} (a @code{AF_} value).
2649 @deffn {Scheme Procedure} addrinfo:socktype ai
2650 Return the socket type for @var{ai} (a @code{SOCK_} value).
2653 @deffn {Scheme Procedure} addrinfo:protocol ai
2654 Return the protocol of @var{ai}.
2657 @deffn {Scheme Procedure} addrinfo:addr ai
2658 Return the socket address associated with @var{ai} as a @code{sockaddr}
2659 object (@pxref{Network Socket Address}).
2662 @deffn {Scheme Procedure} addrinfo:canonname ai
2663 Return a string for the canonical name associated with @var{ai} if
2664 the @code{AI_CANONNAME} flag was supplied.
2667 @subsubheading The Host Database
2668 @cindex @file{/etc/hosts}
2669 @cindex network database
2671 A @dfn{host object} is a structure that represents what is known about a
2672 network host, and is the usual way of representing a system's network
2673 identity inside software.
2675 The following functions accept a host object and return a selected
2678 @deffn {Scheme Procedure} hostent:name host
2679 The ``official'' hostname for @var{host}.
2681 @deffn {Scheme Procedure} hostent:aliases host
2682 A list of aliases for @var{host}.
2684 @deffn {Scheme Procedure} hostent:addrtype host
2685 The host address type, one of the @code{AF} constants, such as
2686 @code{AF_INET} or @code{AF_INET6}.
2688 @deffn {Scheme Procedure} hostent:length host
2689 The length of each address for @var{host}, in bytes.
2691 @deffn {Scheme Procedure} hostent:addr-list host
2692 The list of network addresses associated with @var{host}. For
2693 @code{AF_INET} these are integer IPv4 address (@pxref{Network Address
2697 The following procedures can be used to search the host database. However,
2698 @code{getaddrinfo} should be preferred over them since it's more generic and
2701 @deffn {Scheme Procedure} gethost [host]
2702 @deffnx {Scheme Procedure} gethostbyname hostname
2703 @deffnx {Scheme Procedure} gethostbyaddr address
2704 @deffnx {C Function} scm_gethost (host)
2705 Look up a host by name or address, returning a host object. The
2706 @code{gethost} procedure will accept either a string name or an integer
2707 address; if given no arguments, it behaves like @code{gethostent} (see
2708 below). If a name or address is supplied but the address can not be
2709 found, an error will be thrown to one of the keys:
2710 @code{host-not-found}, @code{try-again}, @code{no-recovery} or
2711 @code{no-data}, corresponding to the equivalent @code{h_error} values.
2712 Unusual conditions may result in errors thrown to the
2713 @code{system-error} or @code{misc_error} keys.
2716 (gethost "www.gnu.org")
2717 @result{} #("www.gnu.org" () 2 4 (3353880842))
2719 (gethostbyname "www.emacs.org")
2720 @result{} #("emacs.org" ("www.emacs.org") 2 4 (1073448978))
2724 The following procedures may be used to step through the host
2725 database from beginning to end.
2727 @deffn {Scheme Procedure} sethostent [stayopen]
2728 Initialize an internal stream from which host objects may be read. This
2729 procedure must be called before any calls to @code{gethostent}, and may
2730 also be called afterward to reset the host entry stream. If
2731 @var{stayopen} is supplied and is not @code{#f}, the database is not
2732 closed by subsequent @code{gethostbyname} or @code{gethostbyaddr} calls,
2733 possibly giving an efficiency gain.
2736 @deffn {Scheme Procedure} gethostent
2737 Return the next host object from the host database, or @code{#f} if
2738 there are no more hosts to be found (or an error has been encountered).
2739 This procedure may not be used before @code{sethostent} has been called.
2742 @deffn {Scheme Procedure} endhostent
2743 Close the stream used by @code{gethostent}. The return value is unspecified.
2746 @deffn {Scheme Procedure} sethost [stayopen]
2747 @deffnx {C Function} scm_sethost (stayopen)
2748 If @var{stayopen} is omitted, this is equivalent to @code{endhostent}.
2749 Otherwise it is equivalent to @code{sethostent stayopen}.
2752 @subsubheading The Network Database
2753 @cindex network database
2755 The following functions accept an object representing a network
2756 and return a selected component:
2758 @deffn {Scheme Procedure} netent:name net
2759 The ``official'' network name.
2761 @deffn {Scheme Procedure} netent:aliases net
2762 A list of aliases for the network.
2764 @deffn {Scheme Procedure} netent:addrtype net
2765 The type of the network number. Currently, this returns only
2768 @deffn {Scheme Procedure} netent:net net
2772 The following procedures are used to search the network database:
2774 @deffn {Scheme Procedure} getnet [net]
2775 @deffnx {Scheme Procedure} getnetbyname net-name
2776 @deffnx {Scheme Procedure} getnetbyaddr net-number
2777 @deffnx {C Function} scm_getnet (net)
2778 Look up a network by name or net number in the network database. The
2779 @var{net-name} argument must be a string, and the @var{net-number}
2780 argument must be an integer. @code{getnet} will accept either type of
2781 argument, behaving like @code{getnetent} (see below) if no arguments are
2785 The following procedures may be used to step through the network
2786 database from beginning to end.
2788 @deffn {Scheme Procedure} setnetent [stayopen]
2789 Initialize an internal stream from which network objects may be read. This
2790 procedure must be called before any calls to @code{getnetent}, and may
2791 also be called afterward to reset the net entry stream. If
2792 @var{stayopen} is supplied and is not @code{#f}, the database is not
2793 closed by subsequent @code{getnetbyname} or @code{getnetbyaddr} calls,
2794 possibly giving an efficiency gain.
2797 @deffn {Scheme Procedure} getnetent
2798 Return the next entry from the network database.
2801 @deffn {Scheme Procedure} endnetent
2802 Close the stream used by @code{getnetent}. The return value is unspecified.
2805 @deffn {Scheme Procedure} setnet [stayopen]
2806 @deffnx {C Function} scm_setnet (stayopen)
2807 If @var{stayopen} is omitted, this is equivalent to @code{endnetent}.
2808 Otherwise it is equivalent to @code{setnetent stayopen}.
2811 @subsubheading The Protocol Database
2812 @cindex @file{/etc/protocols}
2814 @cindex network protocols
2816 The following functions accept an object representing a protocol
2817 and return a selected component:
2819 @deffn {Scheme Procedure} protoent:name protocol
2820 The ``official'' protocol name.
2822 @deffn {Scheme Procedure} protoent:aliases protocol
2823 A list of aliases for the protocol.
2825 @deffn {Scheme Procedure} protoent:proto protocol
2826 The protocol number.
2829 The following procedures are used to search the protocol database:
2831 @deffn {Scheme Procedure} getproto [protocol]
2832 @deffnx {Scheme Procedure} getprotobyname name
2833 @deffnx {Scheme Procedure} getprotobynumber number
2834 @deffnx {C Function} scm_getproto (protocol)
2835 Look up a network protocol by name or by number. @code{getprotobyname}
2836 takes a string argument, and @code{getprotobynumber} takes an integer
2837 argument. @code{getproto} will accept either type, behaving like
2838 @code{getprotoent} (see below) if no arguments are supplied.
2841 The following procedures may be used to step through the protocol
2842 database from beginning to end.
2844 @deffn {Scheme Procedure} setprotoent [stayopen]
2845 Initialize an internal stream from which protocol objects may be read. This
2846 procedure must be called before any calls to @code{getprotoent}, and may
2847 also be called afterward to reset the protocol entry stream. If
2848 @var{stayopen} is supplied and is not @code{#f}, the database is not
2849 closed by subsequent @code{getprotobyname} or @code{getprotobynumber} calls,
2850 possibly giving an efficiency gain.
2853 @deffn {Scheme Procedure} getprotoent
2854 Return the next entry from the protocol database.
2857 @deffn {Scheme Procedure} endprotoent
2858 Close the stream used by @code{getprotoent}. The return value is unspecified.
2861 @deffn {Scheme Procedure} setproto [stayopen]
2862 @deffnx {C Function} scm_setproto (stayopen)
2863 If @var{stayopen} is omitted, this is equivalent to @code{endprotoent}.
2864 Otherwise it is equivalent to @code{setprotoent stayopen}.
2867 @subsubheading The Service Database
2868 @cindex @file{/etc/services}
2870 @cindex network services
2872 The following functions accept an object representing a service
2873 and return a selected component:
2875 @deffn {Scheme Procedure} servent:name serv
2876 The ``official'' name of the network service.
2878 @deffn {Scheme Procedure} servent:aliases serv
2879 A list of aliases for the network service.
2881 @deffn {Scheme Procedure} servent:port serv
2882 The Internet port used by the service.
2884 @deffn {Scheme Procedure} servent:proto serv
2885 The protocol used by the service. A service may be listed many times
2886 in the database under different protocol names.
2889 The following procedures are used to search the service database:
2891 @deffn {Scheme Procedure} getserv [name [protocol]]
2892 @deffnx {Scheme Procedure} getservbyname name protocol
2893 @deffnx {Scheme Procedure} getservbyport port protocol
2894 @deffnx {C Function} scm_getserv (name, protocol)
2895 Look up a network service by name or by service number, and return a
2896 network service object. The @var{protocol} argument specifies the name
2897 of the desired protocol; if the protocol found in the network service
2898 database does not match this name, a system error is signalled.
2900 The @code{getserv} procedure will take either a service name or number
2901 as its first argument; if given no arguments, it behaves like
2902 @code{getservent} (see below).
2905 (getserv "imap" "tcp")
2906 @result{} #("imap2" ("imap") 143 "tcp")
2908 (getservbyport 88 "udp")
2909 @result{} #("kerberos" ("kerberos5" "krb5") 88 "udp")
2913 The following procedures may be used to step through the service
2914 database from beginning to end.
2916 @deffn {Scheme Procedure} setservent [stayopen]
2917 Initialize an internal stream from which service objects may be read. This
2918 procedure must be called before any calls to @code{getservent}, and may
2919 also be called afterward to reset the service entry stream. If
2920 @var{stayopen} is supplied and is not @code{#f}, the database is not
2921 closed by subsequent @code{getservbyname} or @code{getservbyport} calls,
2922 possibly giving an efficiency gain.
2925 @deffn {Scheme Procedure} getservent
2926 Return the next entry from the services database.
2929 @deffn {Scheme Procedure} endservent
2930 Close the stream used by @code{getservent}. The return value is unspecified.
2933 @deffn {Scheme Procedure} setserv [stayopen]
2934 @deffnx {C Function} scm_setserv (stayopen)
2935 If @var{stayopen} is omitted, this is equivalent to @code{endservent}.
2936 Otherwise it is equivalent to @code{setservent stayopen}.
2940 @node Network Socket Address
2941 @subsubsection Network Socket Address
2942 @cindex socket address
2943 @cindex network socket address
2944 @tpindex Socket address
2946 A @dfn{socket address} object identifies a socket endpoint for
2947 communication. In the case of @code{AF_INET} for instance, the socket
2948 address object comprises the host address (or interface on the host)
2949 and a port number which specifies a particular open socket in a
2950 running client or server process. A socket address object can be
2953 @deffn {Scheme Procedure} make-socket-address AF_INET ipv4addr port
2954 @deffnx {Scheme Procedure} make-socket-address AF_INET6 ipv6addr port [flowinfo [scopeid]]
2955 @deffnx {Scheme Procedure} make-socket-address AF_UNIX path
2956 @deffnx {C Function} scm_make_socket_address (family, address, arglist)
2957 Return a new socket address object. The first argument is the address
2958 family, one of the @code{AF} constants, then the arguments vary
2959 according to the family.
2961 For @code{AF_INET} the arguments are an IPv4 network address number
2962 (@pxref{Network Address Conversion}), and a port number.
2964 For @code{AF_INET6} the arguments are an IPv6 network address number
2965 and a port number. Optional @var{flowinfo} and @var{scopeid}
2966 arguments may be given (both integers, default 0).
2968 For @code{AF_UNIX} the argument is a filename (a string).
2970 The C function @code{scm_make_socket_address} takes the @var{family}
2971 and @var{address} arguments directly, then @var{arglist} is a list of
2972 further arguments, being the port for IPv4, port and optional flowinfo
2973 and scopeid for IPv6, or the empty list @code{SCM_EOL} for Unix
2978 The following functions access the fields of a socket address object,
2980 @deffn {Scheme Procedure} sockaddr:fam sa
2981 Return the address family from socket address object @var{sa}. This
2982 is one of the @code{AF} constants (e.g.@: @code{AF_INET}).
2985 @deffn {Scheme Procedure} sockaddr:path sa
2986 For an @code{AF_UNIX} socket address object @var{sa}, return the
2990 @deffn {Scheme Procedure} sockaddr:addr sa
2991 For an @code{AF_INET} or @code{AF_INET6} socket address object
2992 @var{sa}, return the network address number.
2995 @deffn {Scheme Procedure} sockaddr:port sa
2996 For an @code{AF_INET} or @code{AF_INET6} socket address object
2997 @var{sa}, return the port number.
3000 @deffn {Scheme Procedure} sockaddr:flowinfo sa
3001 For an @code{AF_INET6} socket address object @var{sa}, return the
3005 @deffn {Scheme Procedure} sockaddr:scopeid sa
3006 For an @code{AF_INET6} socket address object @var{sa}, return the
3010 @tpindex @code{struct sockaddr}
3011 @tpindex @code{sockaddr}
3012 The functions below convert to and from the C @code{struct sockaddr}
3013 (@pxref{Address Formats,,, libc, The GNU C Library Reference Manual}).
3014 That structure is a generic type, an application can cast to or from
3015 @code{struct sockaddr_in}, @code{struct sockaddr_in6} or @code{struct
3016 sockaddr_un} according to the address family.
3018 In a @code{struct sockaddr} taken or returned, the byte ordering in
3019 the fields follows the C conventions (@pxref{Byte Order,, Byte Order
3020 Conversion, libc, The GNU C Library Reference Manual}). This means
3021 network byte order for @code{AF_INET} host address
3022 (@code{sin_addr.s_addr}) and port number (@code{sin_port}), and
3023 @code{AF_INET6} port number (@code{sin6_port}). But at the Scheme
3024 level these values are taken or returned in host byte order, so the
3025 port is an ordinary integer, and the host address likewise is an
3026 ordinary integer (as described in @ref{Network Address Conversion}).
3028 @deftypefn {C Function} {struct sockaddr *} scm_c_make_socket_address (SCM family, SCM address, SCM args, size_t *outsize)
3029 Return a newly-@code{malloc}ed @code{struct sockaddr} created from
3030 arguments like those taken by @code{scm_make_socket_address} above.
3032 The size (in bytes) of the @code{struct sockaddr} return is stored
3033 into @code{*@var{outsize}}. An application must call @code{free} to
3034 release the returned structure when no longer required.
3037 @deftypefn {C Function} SCM scm_from_sockaddr (const struct sockaddr *address, unsigned address_size)
3038 Return a Scheme socket address object from the C @var{address}
3039 structure. @var{address_size} is the size in bytes of @var{address}.
3042 @deftypefn {C Function} {struct sockaddr *} scm_to_sockaddr (SCM address, size_t *address_size)
3043 Return a newly-@code{malloc}ed @code{struct sockaddr} from a Scheme
3044 level socket address object.
3046 The size (in bytes) of the @code{struct sockaddr} return is stored
3047 into @code{*@var{outsize}}. An application must call @code{free} to
3048 release the returned structure when no longer required.
3052 @node Network Sockets and Communication
3053 @subsubsection Network Sockets and Communication
3055 @cindex network socket
3057 Socket ports can be created using @code{socket} and @code{socketpair}.
3058 The ports are initially unbuffered, to make reading and writing to the
3059 same port more reliable. A buffer can be added to the port using
3060 @code{setvbuf}; see @ref{Ports and File Descriptors}.
3062 Most systems have limits on how many files and sockets can be open, so
3063 it's strongly recommended that socket ports be closed explicitly when
3064 no longer required (@pxref{Ports}).
3066 Some of the underlying C functions take values in network byte order,
3067 but the convention in Guile is that at the Scheme level everything is
3068 ordinary host byte order and conversions are made automatically where
3071 @deffn {Scheme Procedure} socket family style proto
3072 @deffnx {C Function} scm_socket (family, style, proto)
3073 Return a new socket port of the type specified by @var{family},
3074 @var{style} and @var{proto}. All three parameters are integers. The
3075 possible values for @var{family} are as follows, where supported by
3083 The possible values for @var{style} are as follows, again where
3084 supported by the system,
3090 @defvarx SOCK_SEQPACKET
3093 @var{proto} can be obtained from a protocol name using
3094 @code{getprotobyname} (@pxref{Network Databases}). A value of zero
3095 means the default protocol, which is usually right.
3097 A socket cannot by used for communication until it has been connected
3098 somewhere, usually with either @code{connect} or @code{accept} below.
3101 @deffn {Scheme Procedure} socketpair family style proto
3102 @deffnx {C Function} scm_socketpair (family, style, proto)
3103 Return a pair, the @code{car} and @code{cdr} of which are two unnamed
3104 socket ports connected to each other. The connection is full-duplex,
3105 so data can be transferred in either direction between the two.
3107 @var{family}, @var{style} and @var{proto} are as per @code{socket}
3108 above. But many systems only support socket pairs in the
3109 @code{PF_UNIX} family. Zero is likely to be the only meaningful value
3113 @deffn {Scheme Procedure} getsockopt sock level optname
3114 @deffnx {Scheme Procedure} setsockopt sock level optname value
3115 @deffnx {C Function} scm_getsockopt (sock, level, optname)
3116 @deffnx {C Function} scm_setsockopt (sock, level, optname, value)
3117 Get or set an option on socket port @var{sock}. @code{getsockopt}
3118 returns the current value. @code{setsockopt} sets a value and the
3119 return is unspecified.
3121 @var{level} is an integer specifying a protocol layer, either
3122 @code{SOL_SOCKET} for socket level options, or a protocol number from
3123 the @code{IPPROTO} constants or @code{getprotoent} (@pxref{Network
3128 @defvarx IPPROTO_TCP
3129 @defvarx IPPROTO_UDP
3132 @var{optname} is an integer specifying an option within the protocol
3135 For @code{SOL_SOCKET} level the following @var{optname}s are defined
3136 (when provided by the system). For their meaning see
3137 @ref{Socket-Level Options,,, libc, The GNU C Library Reference
3138 Manual}, or @command{man 7 socket}.
3141 @defvarx SO_REUSEADDR
3145 @defvarx SO_DONTROUTE
3146 @defvarx SO_BROADCAST
3149 @defvarx SO_KEEPALIVE
3150 @defvarx SO_OOBINLINE
3151 @defvarx SO_NO_CHECK
3152 @defvarx SO_PRIORITY
3153 @defvarx SO_REUSEPORT
3154 The @var{value} taken or returned is an integer.
3158 The @var{value} taken or returned is a pair of integers
3159 @code{(@var{ENABLE} . @var{TIMEOUT})}. On old systems without timeout
3160 support (ie.@: without @code{struct linger}), only @var{ENABLE} has an
3161 effect but the value in Guile is always a pair.
3164 @c Note that we refer only to ``man ip'' here. On GNU/Linux it's
3165 @c ``man 7 ip'' but on NetBSD it's ``man 4 ip''.
3167 For IP level (@code{IPPROTO_IP}) the following @var{optname}s are
3168 defined (when provided by the system). See @command{man ip} for what
3171 @defvar IP_MULTICAST_IF
3172 This sets the source interface used by multicast traffic.
3175 @defvar IP_MULTICAST_TTL
3176 This sets the default TTL for multicast traffic. This defaults
3177 to 1 and should be increased to allow traffic to pass beyond the
3181 @defvar IP_ADD_MEMBERSHIP
3182 @defvarx IP_DROP_MEMBERSHIP
3183 These can be used only with @code{setsockopt}, not @code{getsockopt}.
3184 @var{value} is a pair @code{(@var{MULTIADDR} . @var{INTERFACEADDR})}
3185 of integer IPv4 addresses (@pxref{Network Address Conversion}).
3186 @var{MULTIADDR} is a multicast address to be added to or dropped from
3187 the interface @var{INTERFACEADDR}. @var{INTERFACEADDR} can be
3188 @code{INADDR_ANY} to have the system select the interface.
3189 @var{INTERFACEADDR} can also be an interface index number, on systems
3194 @deffn {Scheme Procedure} shutdown sock how
3195 @deffnx {C Function} scm_shutdown (sock, how)
3196 Sockets can be closed simply by using @code{close-port}. The
3197 @code{shutdown} procedure allows reception or transmission on a
3198 connection to be shut down individually, according to the parameter
3203 Stop receiving data for this socket. If further data arrives, reject it.
3205 Stop trying to transmit data from this socket. Discard any
3206 data waiting to be sent. Stop looking for acknowledgement of
3207 data already sent; don't retransmit it if it is lost.
3209 Stop both reception and transmission.
3212 The return value is unspecified.
3215 @deffn {Scheme Procedure} connect sock sockaddr
3216 @deffnx {Scheme Procedure} connect sock AF_INET ipv4addr port
3217 @deffnx {Scheme Procedure} connect sock AF_INET6 ipv6addr port [flowinfo [scopeid]]
3218 @deffnx {Scheme Procedure} connect sock AF_UNIX path
3219 @deffnx {C Function} scm_connect (sock, fam, address, args)
3220 Initiate a connection on socket port @var{sock} to a given address.
3221 The destination is either a socket address object, or arguments the
3222 same as @code{make-socket-address} would take to make such an object
3223 (@pxref{Network Socket Address}). The return value is unspecified.
3226 (connect sock AF_INET INADDR_LOOPBACK 23)
3227 (connect sock (make-socket-address AF_INET INADDR_LOOPBACK 23))
3231 @deffn {Scheme Procedure} bind sock sockaddr
3232 @deffnx {Scheme Procedure} bind sock AF_INET ipv4addr port
3233 @deffnx {Scheme Procedure} bind sock AF_INET6 ipv6addr port [flowinfo [scopeid]]
3234 @deffnx {Scheme Procedure} bind sock AF_UNIX path
3235 @deffnx {C Function} scm_bind (sock, fam, address, args)
3236 Bind socket port @var{sock} to the given address. The address is
3237 either a socket address object, or arguments the same as
3238 @code{make-socket-address} would take to make such an object
3239 (@pxref{Network Socket Address}). The return value is unspecified.
3241 Generally a socket is only explicitly bound to a particular address
3242 when making a server, i.e.@: to listen on a particular port. For an
3243 outgoing connection the system will assign a local address
3244 automatically, if not already bound.
3247 (bind sock AF_INET INADDR_ANY 12345)
3248 (bind sock (make-socket-address AF_INET INADDR_ANY 12345))
3252 @deffn {Scheme Procedure} listen sock backlog
3253 @deffnx {C Function} scm_listen (sock, backlog)
3254 Enable @var{sock} to accept connection
3255 requests. @var{backlog} is an integer specifying
3256 the maximum length of the queue for pending connections.
3257 If the queue fills, new clients will fail to connect until
3258 the server calls @code{accept} to accept a connection from
3261 The return value is unspecified.
3264 @deffn {Scheme Procedure} accept sock
3265 @deffnx {C Function} scm_accept (sock)
3266 Accept a connection from socket port @var{sock} which has been enabled
3267 for listening with @code{listen} above. If there are no incoming
3268 connections in the queue, wait until one is available (unless
3269 @code{O_NONBLOCK} has been set on the socket, @pxref{Ports and File
3270 Descriptors,@code{fcntl}}).
3272 The return value is a pair. The @code{car} is a new socket port,
3273 connected and ready to communicate. The @code{cdr} is a socket
3274 address object (@pxref{Network Socket Address}) which is where the
3275 remote connection is from (like @code{getpeername} below).
3277 All communication takes place using the new socket returned. The
3278 given @var{sock} remains bound and listening, and @code{accept} may be
3279 called on it again to get another incoming connection when desired.
3282 @deffn {Scheme Procedure} getsockname sock
3283 @deffnx {C Function} scm_getsockname (sock)
3284 Return a socket address object which is the where @var{sock} is bound
3285 locally. @var{sock} may have obtained its local address from
3286 @code{bind} (above), or if a @code{connect} is done with an otherwise
3287 unbound socket (which is usual) then the system will have assigned an
3290 Note that on many systems the address of a socket in the
3291 @code{AF_UNIX} namespace cannot be read.
3294 @deffn {Scheme Procedure} getpeername sock
3295 @deffnx {C Function} scm_getpeername (sock)
3296 Return a socket address object which is where @var{sock} is connected
3297 to, i.e.@: the remote endpoint.
3299 Note that on many systems the address of a socket in the
3300 @code{AF_UNIX} namespace cannot be read.
3303 @deffn {Scheme Procedure} recv! sock buf [flags]
3304 @deffnx {C Function} scm_recv (sock, buf, flags)
3305 Receive data from a socket port.
3306 @var{sock} must already
3307 be bound to the address from which data is to be received.
3308 @var{buf} is a bytevector into which
3309 the data will be written. The size of @var{buf} limits
3311 data which can be received: in the case of packet
3312 protocols, if a packet larger than this limit is encountered
3314 will be irrevocably lost.
3318 @vindex MSG_DONTROUTE
3319 The optional @var{flags} argument is a value or bitwise OR of
3320 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3322 The value returned is the number of bytes read from the
3325 Note that the data is read directly from the socket file
3327 any unread buffered port data is ignored.
3330 @deffn {Scheme Procedure} send sock message [flags]
3331 @deffnx {C Function} scm_send (sock, message, flags)
3334 @vindex MSG_DONTROUTE
3335 Transmit bytevector @var{message} on socket port @var{sock}.
3336 @var{sock} must already be bound to a destination address. The value
3337 returned is the number of bytes transmitted---it's possible for this
3338 to be less than the length of @var{message} if the socket is set to be
3339 non-blocking. The optional @var{flags} argument is a value or bitwise
3340 OR of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3342 Note that the data is written directly to the socket
3344 any unflushed buffered port data is ignored.
3347 @deffn {Scheme Procedure} recvfrom! sock buf [flags [start [end]]]
3348 @deffnx {C Function} scm_recvfrom (sock, buf, flags, start, end)
3349 Receive data from socket port @var{sock}, returning the originating
3350 address as well as the data. This function is usually for datagram
3351 sockets, but can be used on stream-oriented sockets too.
3353 The data received is stored in bytevector @var{buf}, using
3354 either the whole bytevector or just the region between the optional
3355 @var{start} and @var{end} positions. The size of @var{buf}
3356 limits the amount of data that can be received. For datagram
3357 protocols if a packet larger than this is received then excess
3358 bytes are irrevocably lost.
3360 The return value is a pair. The @code{car} is the number of bytes
3361 read. The @code{cdr} is a socket address object (@pxref{Network
3362 Socket Address}) which is where the data came from, or @code{#f} if
3363 the origin is unknown.
3367 @vindex MSG_DONTROUTE
3368 The optional @var{flags} argument is a or bitwise-OR (@code{logior})
3369 of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3371 Data is read directly from the socket file descriptor, any buffered
3372 port data is ignored.
3374 @c This was linux kernel 2.6.15 and glibc 2.3.6, not sure what any
3375 @c specs are supposed to say about recvfrom threading.
3377 On a GNU/Linux system @code{recvfrom!} is not multi-threading, all
3378 threads stop while a @code{recvfrom!} call is in progress. An
3379 application may need to use @code{select}, @code{O_NONBLOCK} or
3380 @code{MSG_DONTWAIT} to avoid this.
3383 @deffn {Scheme Procedure} sendto sock message sockaddr [flags]
3384 @deffnx {Scheme Procedure} sendto sock message AF_INET ipv4addr port [flags]
3385 @deffnx {Scheme Procedure} sendto sock message AF_INET6 ipv6addr port [flowinfo [scopeid [flags]]]
3386 @deffnx {Scheme Procedure} sendto sock message AF_UNIX path [flags]
3387 @deffnx {C Function} scm_sendto (sock, message, fam, address, args_and_flags)
3388 Transmit bytevector @var{message} as a datagram socket port
3389 @var{sock}. The destination is specified either as a socket address
3390 object, or as arguments the same as would be taken by
3391 @code{make-socket-address} to create such an object (@pxref{Network
3394 The destination address may be followed by an optional @var{flags}
3395 argument which is a @code{logior} (@pxref{Bitwise Operations}) of
3396 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3398 The value returned is the number of bytes transmitted --
3400 this to be less than the length of @var{message} if the
3402 set to be non-blocking.
3403 Note that the data is written directly to the socket
3405 any unflushed buffered port data is ignored.
3409 @node Internet Socket Examples
3410 @subsubsection Network Socket Examples
3411 @cindex network examples
3412 @cindex socket examples
3414 The following give examples of how to use network sockets.
3416 @subsubheading Internet Socket Client Example
3418 @cindex socket client example
3419 The following example demonstrates an Internet socket client.
3420 It connects to the HTTP daemon running on the local machine and
3421 returns the contents of the root index URL.
3424 (let ((s (socket PF_INET SOCK_STREAM 0)))
3425 (connect s AF_INET (inet-pton AF_INET "127.0.0.1") 80)
3426 (display "GET / HTTP/1.0\r\n\r\n" s)
3428 (do ((line (read-line s) (read-line s)))
3429 ((eof-object? line))
3435 @subsubheading Internet Socket Server Example
3437 @cindex socket server example
3438 The following example shows a simple Internet server which listens on
3439 port 2904 for incoming connections and sends a greeting back to the
3443 (let ((s (socket PF_INET SOCK_STREAM 0)))
3444 (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
3445 ;; @r{Specific address?}
3446 ;; @r{(bind s AF_INET (inet-pton AF_INET "127.0.0.1") 2904)}
3447 (bind s AF_INET INADDR_ANY 2904)
3450 (simple-format #t "Listening for clients in pid: ~S" (getpid))
3454 (let* ((client-connection (accept s))
3455 (client-details (cdr client-connection))
3456 (client (car client-connection)))
3457 (simple-format #t "Got new client connection: ~S"
3460 (simple-format #t "Client address: ~S"
3462 (sockaddr:addr client-details)))
3464 ;; @r{Send back the greeting to the client port}
3465 (display "Hello client\r\n" client)
3470 @node System Identification
3471 @subsection System Identification
3474 This section lists the various procedures Guile provides for accessing
3475 information about the system it runs on.
3477 @deffn {Scheme Procedure} uname
3478 @deffnx {C Function} scm_uname ()
3479 Return an object with some information about the computer
3480 system the program is running on.
3482 The following procedures accept an object as returned by @code{uname}
3483 and return a selected component (all of which are strings).
3485 @deffn {Scheme Procedure} utsname:sysname un
3486 The name of the operating system.
3488 @deffn {Scheme Procedure} utsname:nodename un
3489 The network name of the computer.
3491 @deffn {Scheme Procedure} utsname:release un
3492 The current release level of the operating system implementation.
3494 @deffn {Scheme Procedure} utsname:version un
3495 The current version level within the release of the operating system.
3497 @deffn {Scheme Procedure} utsname:machine un
3498 A description of the hardware.
3502 @deffn {Scheme Procedure} gethostname
3503 @deffnx {C Function} scm_gethostname ()
3505 Return the host name of the current processor.
3508 @deffn {Scheme Procedure} sethostname name
3509 @deffnx {C Function} scm_sethostname (name)
3510 Set the host name of the current processor to @var{name}. May
3511 only be used by the superuser. The return value is not
3519 @deffn {Scheme Procedure} setlocale category [locale]
3520 @deffnx {C Function} scm_setlocale (category, locale)
3521 Get or set the current locale, used for various internationalizations.
3522 Locales are strings, such as @samp{sv_SE}.
3524 If @var{locale} is given then the locale for the given @var{category}
3525 is set and the new value returned. If @var{locale} is not given then
3526 the current value is returned. @var{category} should be one of the
3527 following values (@pxref{Locale Categories, Categories of Activities
3528 that Locales Affect,, libc, The GNU C Library Reference Manual}):
3533 @defvarx LC_MESSAGES
3534 @defvarx LC_MONETARY
3540 A common usage is @samp{(setlocale LC_ALL "")}, which initializes all
3541 categories based on standard environment variables (@code{LANG} etc).
3542 For full details on categories and locale names @pxref{Locales,,
3543 Locales and Internationalization, libc, The GNU C Library Reference
3546 Note that @code{setlocale} affects locale settings for the whole
3547 process. @xref{i18n Introduction, locale objects and
3548 @code{make-locale}}, for a thread-safe alternative.
3552 @subsection Encryption
3555 Please note that the procedures in this section are not suited for
3556 strong encryption, they are only interfaces to the well-known and
3557 common system library functions of the same name. They are just as good
3558 (or bad) as the underlying functions, so you should refer to your system
3559 documentation before using them (@pxref{crypt,, Encrypting Passwords,
3560 libc, The GNU C Library Reference Manual}).
3562 @deffn {Scheme Procedure} crypt key salt
3563 @deffnx {C Function} scm_crypt (key, salt)
3564 Encrypt @var{key}, with the addition of @var{salt} (both strings),
3565 using the @code{crypt} C library call.
3568 Although @code{getpass} is not an encryption procedure per se, it
3569 appears here because it is often used in combination with @code{crypt}:
3571 @deffn {Scheme Procedure} getpass prompt
3572 @deffnx {C Function} scm_getpass (prompt)
3574 Display @var{prompt} to the standard error output and read
3575 a password from @file{/dev/tty}. If this file is not
3576 accessible, it reads from standard input. The password may be
3577 up to 127 characters in length. Additional characters and the
3578 terminating newline character are discarded. While reading
3579 the password, echoing and the generation of signals by special
3580 characters is disabled.
3585 @c TeX-master: "guile.texi"