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 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.
475 @deffn {Scheme Procedure} fcntl port/fd cmd [value]
476 @deffnx {C Function} scm_fcntl (object, cmd, value)
477 Apply @var{cmd} on @var{port/fd}, either a port or file descriptor.
478 The @var{value} argument is used by the @code{SET} commands described
479 below, it's an integer value.
481 Values for @var{cmd} are:
484 Duplicate the file descriptor, the same as @code{dup->fdes} above
490 Get or set flags associated with the file descriptor. The only flag
494 ``Close on exec'', meaning the file descriptor will be closed on an
495 @code{exec} call (a successful such call). For example to set that
499 (fcntl port F_SETFD FD_CLOEXEC)
502 Or better, set it but leave any other possible future flags unchanged,
505 (fcntl port F_SETFD (logior FD_CLOEXEC
506 (fcntl port F_GETFD)))
513 Get or set flags associated with the open file. These flags are
514 @code{O_RDONLY} etc described under @code{open} above.
516 A common use is to set @code{O_NONBLOCK} on a network socket. The
517 following sets that flag, and leaves other flags unchanged.
520 (fcntl sock F_SETFL (logior O_NONBLOCK
521 (fcntl sock F_GETFL)))
527 Get or set the process ID of a socket's owner, for @code{SIGIO} signals.
531 @deffn {Scheme Procedure} flock file operation
532 @deffnx {C Function} scm_flock (file, operation)
534 Apply or remove an advisory lock on an open file.
535 @var{operation} specifies the action to be done:
538 Shared lock. More than one process may hold a shared lock
539 for a given file at a given time.
542 Exclusive lock. Only one process may hold an exclusive lock
543 for a given file at a given time.
549 Don't block when locking. This is combined with one of the other
550 operations using @code{logior} (@pxref{Bitwise Operations}). If
551 @code{flock} would block an @code{EWOULDBLOCK} error is thrown
552 (@pxref{Conventions}).
555 The return value is not specified. @var{file} may be an open
556 file descriptor or an open file descriptor port.
558 Note that @code{flock} does not lock files across NFS.
561 @deffn {Scheme Procedure} select reads writes excepts [secs [usecs]]
562 @deffnx {C Function} scm_select (reads, writes, excepts, secs, usecs)
563 This procedure has a variety of uses: waiting for the ability
564 to provide input, accept output, or the existence of
565 exceptional conditions on a collection of ports or file
566 descriptors, or waiting for a timeout to occur.
567 It also returns if interrupted by a signal.
569 @var{reads}, @var{writes} and @var{excepts} can be lists or
570 vectors, with each member a port or a file descriptor.
571 The value returned is a list of three corresponding
572 lists or vectors containing only the members which meet the
573 specified requirement. The ability of port buffers to
574 provide input or accept output is taken into account.
575 Ordering of the input lists or vectors is not preserved.
577 The optional arguments @var{secs} and @var{usecs} specify the
578 timeout. Either @var{secs} can be specified alone, as
579 either an integer or a real number, or both @var{secs} and
580 @var{usecs} can be specified as integers, in which case
581 @var{usecs} is an additional timeout expressed in
582 microseconds. If @var{secs} is omitted or is @code{#f} then
583 select will wait for as long as it takes for one of the other
584 conditions to be satisfied.
586 The scsh version of @code{select} differs as follows:
587 Only vectors are accepted for the first three arguments.
588 The @var{usecs} argument is not supported.
589 Multiple values are returned instead of a list.
590 Duplicates in the input vectors appear only once in output.
591 An additional @code{select!} interface is provided.
595 @subsection File System
598 These procedures allow querying and setting file system attributes
600 permissions, sizes and types of files); deleting, copying, renaming and
601 linking files; creating and removing directories and querying their
602 contents; syncing the file system and creating special files.
604 @deffn {Scheme Procedure} access? path how
605 @deffnx {C Function} scm_access (path, how)
606 Test accessibility of a file under the real UID and GID of the calling
607 process. The return is @code{#t} if @var{path} exists and the
608 permissions requested by @var{how} are all allowed, or @code{#f} if
611 @var{how} is an integer which is one of the following values, or a
612 bitwise-OR (@code{logior}) of multiple values.
615 Test for read permission.
618 Test for write permission.
621 Test for execute permission.
624 Test for existence of the file. This is implied by each of the other
625 tests, so there's no need to combine it with them.
628 It's important to note that @code{access?} does not simply indicate
629 what will happen on attempting to read or write a file. In normal
630 circumstances it does, but in a set-UID or set-GID program it doesn't
631 because @code{access?} tests the real ID, whereas an open or execute
632 attempt uses the effective ID.
634 A program which will never run set-UID/GID can ignore the difference
635 between real and effective IDs, but for maximum generality, especially
636 in library functions, it's best not to use @code{access?} to predict
637 the result of an open or execute, instead simply attempt that and
640 The main use for @code{access?} is to let a set-UID/GID program
641 determine what the invoking user would have been allowed to do,
642 without the greater (or perhaps lesser) privileges afforded by the
643 effective ID. For more on this, see @ref{Testing File Access,,, libc,
644 The GNU C Library Reference Manual}.
648 @deffn {Scheme Procedure} stat object
649 @deffnx {C Function} scm_stat (object)
650 Return an object containing various information about the file
651 determined by @var{object}. @var{object} can be a string containing
652 a file name or a port or integer file descriptor which is open
653 on a file (in which case @code{fstat} is used as the underlying
656 The object returned by @code{stat} can be passed as a single
657 parameter to the following procedures, all of which return
660 @deffn {Scheme Procedure} stat:dev st
661 The device number containing the file.
663 @deffn {Scheme Procedure} stat:ino st
664 The file serial number, which distinguishes this file from all
665 other files on the same device.
667 @deffn {Scheme Procedure} stat:mode st
668 The mode of the file. This is an integer which incorporates file type
669 information and file permission bits. See also @code{stat:type} and
670 @code{stat:perms} below.
672 @deffn {Scheme Procedure} stat:nlink st
673 The number of hard links to the file.
675 @deffn {Scheme Procedure} stat:uid st
676 The user ID of the file's owner.
678 @deffn {Scheme Procedure} stat:gid st
679 The group ID of the file.
681 @deffn {Scheme Procedure} stat:rdev st
682 Device ID; this entry is defined only for character or block special
683 files. On some systems this field is not available at all, in which
684 case @code{stat:rdev} returns @code{#f}.
686 @deffn {Scheme Procedure} stat:size st
687 The size of a regular file in bytes.
689 @deffn {Scheme Procedure} stat:atime st
690 The last access time for the file, in seconds.
692 @deffn {Scheme Procedure} stat:mtime st
693 The last modification time for the file, in seconds.
695 @deffn {Scheme Procedure} stat:ctime st
696 The last modification time for the attributes of the file, in seconds.
698 @deffn {Scheme Procedure} stat:atimensec st
699 @deffnx {Scheme Procedure} stat:mtimensec st
700 @deffnx {Scheme Procedure} stat:ctimensec st
701 The fractional part of a file's access, modification, or attribute modification
702 time, in nanoseconds. Nanosecond timestamps are only available on some operating
703 systems and file systems. If Guile cannot retrieve nanosecond-level timestamps
704 for a file, these fields will be set to 0.
706 @deffn {Scheme Procedure} stat:blksize st
707 The optimal block size for reading or writing the file, in bytes. On
708 some systems this field is not available, in which case
709 @code{stat:blksize} returns a sensible suggested block size.
711 @deffn {Scheme Procedure} stat:blocks st
712 The amount of disk space that the file occupies measured in units of
713 512 byte blocks. On some systems this field is not available, in
714 which case @code{stat:blocks} returns @code{#f}.
717 In addition, the following procedures return the information
718 from @code{stat:mode} in a more convenient form:
720 @deffn {Scheme Procedure} stat:type st
721 A symbol representing the type of file. Possible values are
722 @samp{regular}, @samp{directory}, @samp{symlink},
723 @samp{block-special}, @samp{char-special}, @samp{fifo}, @samp{socket},
726 @deffn {Scheme Procedure} stat:perms st
727 An integer representing the access permission bits.
731 @deffn {Scheme Procedure} lstat path
732 @deffnx {C Function} scm_lstat (path)
733 Similar to @code{stat}, but does not follow symbolic links, i.e.,
734 it will return information about a symbolic link itself, not the
735 file it points to. @var{path} must be a string.
738 @deffn {Scheme Procedure} readlink path
739 @deffnx {C Function} scm_readlink (path)
740 Return the value of the symbolic link named by @var{path} (a
741 string), i.e., the file that the link points to.
746 @deffn {Scheme Procedure} chown object owner group
747 @deffnx {C Function} scm_chown (object, owner, group)
748 Change the ownership and group of the file referred to by @var{object}
749 to the integer values @var{owner} and @var{group}. @var{object} can
750 be a string containing a file name or, if the platform supports
751 @code{fchown} (@pxref{File Owner,,,libc,The GNU C Library Reference
752 Manual}), a port or integer file descriptor which is open on the file.
753 The return value is unspecified.
755 If @var{object} is a symbolic link, either the
756 ownership of the link or the ownership of the referenced file will be
757 changed depending on the operating system (lchown is
758 unsupported at present). If @var{owner} or @var{group} is specified
759 as @code{-1}, then that ID is not changed.
763 @deffn {Scheme Procedure} chmod object mode
764 @deffnx {C Function} scm_chmod (object, mode)
765 Changes the permissions of the file referred to by @var{object}.
766 @var{object} can be a string containing a file name or a port or integer file
767 descriptor which is open on a file (in which case @code{fchmod} is used
768 as the underlying system call).
770 the new permissions as a decimal number, e.g., @code{(chmod "foo" #o755)}.
771 The return value is unspecified.
774 @deffn {Scheme Procedure} utime pathname [actime [modtime [actimens [modtimens [flags]]]]]
775 @deffnx {C Function} scm_utime (pathname, actime, modtime, actimens, modtimens, flags)
776 @code{utime} sets the access and modification times for the
777 file named by @var{pathname}. If @var{actime} or @var{modtime} is
778 not supplied, then the current time is used. @var{actime} and
779 @var{modtime} must be integer time values as returned by the
780 @code{current-time} procedure.
782 The optional @var{actimens} and @var{modtimens} are nanoseconds
783 to add @var{actime} and @var{modtime}. Nanosecond precision is
784 only supported on some combinations of file systems and operating
787 (utime "foo" (- (current-time) 3600))
789 will set the access time to one hour in the past and the
790 modification time to the current time.
794 @deffn {Scheme Procedure} delete-file str
795 @deffnx {C Function} scm_delete_file (str)
796 Deletes (or ``unlinks'') the file whose path is specified by
800 @deffn {Scheme Procedure} copy-file oldfile newfile
801 @deffnx {C Function} scm_copy_file (oldfile, newfile)
802 Copy the file specified by @var{oldfile} to @var{newfile}.
803 The return value is unspecified.
806 @deffn {Scheme Procedure} sendfile out in count [offset]
807 @deffnx {C Function} scm_sendfile (out, in, count, offset)
808 Send @var{count} bytes from @var{in} to @var{out}, both of which
809 are either open file ports or file descriptors. When
810 @var{offset} is omitted, start reading from @var{in}'s current
811 position; otherwise, start reading at @var{offset}.
813 When @var{in} is a port, it is often preferable to specify @var{offset},
814 because @var{in}'s offset as a port may be different from the offset of
815 its underlying file descriptor.
817 On systems that support it, such as GNU/Linux, this procedure uses the
818 @code{sendfile} libc function, which usually corresponds to a system
819 call. This is faster than doing a series of @code{read} and
820 @code{write} system calls. A typical application is to send a file over
823 In some cases, the @code{sendfile} libc function may return
824 @code{EINVAL} or @code{ENOSYS}. In that case, Guile's @code{sendfile}
825 procedure automatically falls back to doing a series of @code{read} and
830 @deffn {Scheme Procedure} rename-file oldname newname
831 @deffnx {C Function} scm_rename (oldname, newname)
832 Renames the file specified by @var{oldname} to @var{newname}.
833 The return value is unspecified.
836 @deffn {Scheme Procedure} link oldpath newpath
837 @deffnx {C Function} scm_link (oldpath, newpath)
838 Creates a new name @var{newpath} in the file system for the
839 file named by @var{oldpath}. If @var{oldpath} is a symbolic
840 link, the link may or may not be followed depending on the
844 @deffn {Scheme Procedure} symlink oldpath newpath
845 @deffnx {C Function} scm_symlink (oldpath, newpath)
846 Create a symbolic link named @var{newpath} with the value (i.e., pointing to)
847 @var{oldpath}. The return value is unspecified.
850 @deffn {Scheme Procedure} mkdir path [mode]
851 @deffnx {C Function} scm_mkdir (path, mode)
852 Create a new directory named by @var{path}. If @var{mode} is omitted
853 then the permissions of the directory file are set using the current
854 umask (@pxref{Processes}). Otherwise they are set to the decimal
855 value specified with @var{mode}. The return value is unspecified.
858 @deffn {Scheme Procedure} rmdir path
859 @deffnx {C Function} scm_rmdir (path)
860 Remove the existing directory named by @var{path}. The directory must
861 be empty for this to succeed. The return value is unspecified.
864 @deffn {Scheme Procedure} opendir dirname
865 @deffnx {C Function} scm_opendir (dirname)
866 @cindex directory contents
867 Open the directory specified by @var{dirname} and return a directory
870 Before using this and the procedures below, make sure to see the
871 higher-level procedures for directory traversal that are available
872 (@pxref{File Tree Walk}).
875 @deffn {Scheme Procedure} directory-stream? object
876 @deffnx {C Function} scm_directory_stream_p (object)
877 Return a boolean indicating whether @var{object} is a directory
878 stream as returned by @code{opendir}.
881 @deffn {Scheme Procedure} readdir stream
882 @deffnx {C Function} scm_readdir (stream)
883 Return (as a string) the next directory entry from the directory stream
884 @var{stream}. If there is no remaining entry to be read then the
885 end of file object is returned.
888 @deffn {Scheme Procedure} rewinddir stream
889 @deffnx {C Function} scm_rewinddir (stream)
890 Reset the directory port @var{stream} so that the next call to
891 @code{readdir} will return the first directory entry.
894 @deffn {Scheme Procedure} closedir stream
895 @deffnx {C Function} scm_closedir (stream)
896 Close the directory stream @var{stream}.
897 The return value is unspecified.
900 Here is an example showing how to display all the entries in a
904 (define dir (opendir "/usr/lib"))
905 (do ((entry (readdir dir) (readdir dir)))
906 ((eof-object? entry))
907 (display entry)(newline))
911 @deffn {Scheme Procedure} sync
912 @deffnx {C Function} scm_sync ()
913 Flush the operating system disk buffers.
914 The return value is unspecified.
917 @deffn {Scheme Procedure} mknod path type perms dev
918 @deffnx {C Function} scm_mknod (path, type, perms, dev)
920 Creates a new special file, such as a file corresponding to a device.
921 @var{path} specifies the name of the file. @var{type} should be one
922 of the following symbols: @samp{regular}, @samp{directory},
923 @samp{symlink}, @samp{block-special}, @samp{char-special},
924 @samp{fifo}, or @samp{socket}. @var{perms} (an integer) specifies the
925 file permissions. @var{dev} (an integer) specifies which device the
926 special file refers to. Its exact interpretation depends on the kind
927 of special file being created.
931 (mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))
934 The return value is unspecified.
937 @deffn {Scheme Procedure} tmpnam
938 @deffnx {C Function} scm_tmpnam ()
939 @cindex temporary file
940 Return an auto-generated name of a temporary file, a file which
941 doesn't already exist. The name includes a path, it's usually in
942 @file{/tmp} but that's system dependent.
944 Care must be taken when using @code{tmpnam}. In between choosing the
945 name and creating the file another program might use that name, or an
946 attacker might even make it a symlink pointing at something important
947 and causing you to overwrite that.
949 The safe way is to create the file using @code{open} with
950 @code{O_EXCL} to avoid any overwriting. A loop can try again with
951 another name if the file exists (error @code{EEXIST}).
952 @code{mkstemp!} below does that.
955 @deffn {Scheme Procedure} mkstemp! tmpl
956 @deffnx {C Function} scm_mkstemp (tmpl)
957 @cindex temporary file
958 Create a new unique file in the file system and return a new buffered
959 port open for reading and writing to the file.
961 @var{tmpl} is a string specifying where the file should be created: it
962 must end with @samp{XXXXXX} and those @samp{X}s will be changed in the
963 string to return the name of the file. (@code{port-filename} on the
964 port also gives the name.)
966 POSIX doesn't specify the permissions mode of the file, on GNU and
967 most systems it's @code{#o600}. An application can use @code{chmod}
968 to relax that if desired. For example @code{#o666} less @code{umask},
969 which is usual for ordinary file creation,
972 (let ((port (mkstemp! (string-copy "/tmp/myfile-XXXXXX"))))
973 (chmod port (logand #o666 (lognot (umask))))
978 @deffn {Scheme Procedure} tmpfile
979 @deffnx {C Function} scm_tmpfile ()
980 Return an input/output port to a unique temporary file
981 named using the path prefix @code{P_tmpdir} defined in
983 The file is automatically deleted when the port is closed
984 or the program terminates.
987 @deffn {Scheme Procedure} dirname filename
988 @deffnx {C Function} scm_dirname (filename)
989 Return the directory name component of the file name
990 @var{filename}. If @var{filename} does not contain a directory
991 component, @code{.} is returned.
994 @deffn {Scheme Procedure} basename filename [suffix]
995 @deffnx {C Function} scm_basename (filename, suffix)
996 Return the base name of the file name @var{filename}. The
997 base name is the file name without any directory components.
998 If @var{suffix} is provided, and is equal to the end of
999 @var{basename}, it is removed also.
1002 (basename "/tmp/test.xml" ".xml")
1007 @deffn {Scheme Procedure} file-exists? filename
1008 Return @code{#t} if the file named @var{filename} exists, @code{#f} if
1013 @node User Information
1014 @subsection User Information
1015 @cindex user information
1016 @cindex password file
1019 The facilities in this section provide an interface to the user and
1021 They should be used with care since they are not reentrant.
1023 The following functions accept an object representing user information
1024 and return a selected component:
1026 @deffn {Scheme Procedure} passwd:name pw
1027 The name of the userid.
1029 @deffn {Scheme Procedure} passwd:passwd pw
1030 The encrypted passwd.
1032 @deffn {Scheme Procedure} passwd:uid pw
1035 @deffn {Scheme Procedure} passwd:gid pw
1036 The group id number.
1038 @deffn {Scheme Procedure} passwd:gecos pw
1041 @deffn {Scheme Procedure} passwd:dir pw
1044 @deffn {Scheme Procedure} passwd:shell pw
1049 @deffn {Scheme Procedure} getpwuid uid
1050 Look up an integer userid in the user database.
1053 @deffn {Scheme Procedure} getpwnam name
1054 Look up a user name string in the user database.
1057 @deffn {Scheme Procedure} setpwent
1058 Initializes a stream used by @code{getpwent} to read from the user database.
1059 The next use of @code{getpwent} will return the first entry. The
1060 return value is unspecified.
1063 @deffn {Scheme Procedure} getpwent
1064 Read the next entry in the user database stream. The return is a
1065 passwd user object as above, or @code{#f} when no more entries.
1068 @deffn {Scheme Procedure} endpwent
1069 Closes the stream used by @code{getpwent}. The return value is unspecified.
1072 @deffn {Scheme Procedure} setpw [arg]
1073 @deffnx {C Function} scm_setpwent (arg)
1074 If called with a true argument, initialize or reset the password data
1075 stream. Otherwise, close the stream. The @code{setpwent} and
1076 @code{endpwent} procedures are implemented on top of this.
1079 @deffn {Scheme Procedure} getpw [user]
1080 @deffnx {C Function} scm_getpwuid (user)
1081 Look up an entry in the user database. @var{user} can be an integer,
1082 a string, or omitted, giving the behaviour of getpwuid, getpwnam
1083 or getpwent respectively.
1086 The following functions accept an object representing group information
1087 and return a selected component:
1089 @deffn {Scheme Procedure} group:name gr
1092 @deffn {Scheme Procedure} group:passwd gr
1093 The encrypted group password.
1095 @deffn {Scheme Procedure} group:gid gr
1096 The group id number.
1098 @deffn {Scheme Procedure} group:mem gr
1099 A list of userids which have this group as a supplementary group.
1103 @deffn {Scheme Procedure} getgrgid gid
1104 Look up an integer group id in the group database.
1107 @deffn {Scheme Procedure} getgrnam name
1108 Look up a group name in the group database.
1111 @deffn {Scheme Procedure} setgrent
1112 Initializes a stream used by @code{getgrent} to read from the group database.
1113 The next use of @code{getgrent} will return the first entry.
1114 The return value is unspecified.
1117 @deffn {Scheme Procedure} getgrent
1118 Return the next entry in the group database, using the stream set by
1122 @deffn {Scheme Procedure} endgrent
1123 Closes the stream used by @code{getgrent}.
1124 The return value is unspecified.
1127 @deffn {Scheme Procedure} setgr [arg]
1128 @deffnx {C Function} scm_setgrent (arg)
1129 If called with a true argument, initialize or reset the group data
1130 stream. Otherwise, close the stream. The @code{setgrent} and
1131 @code{endgrent} procedures are implemented on top of this.
1134 @deffn {Scheme Procedure} getgr [group]
1135 @deffnx {C Function} scm_getgrgid (group)
1136 Look up an entry in the group database. @var{group} can be an integer,
1137 a string, or omitted, giving the behaviour of getgrgid, getgrnam
1138 or getgrent respectively.
1141 In addition to the accessor procedures for the user database, the
1142 following shortcut procedure is also available.
1144 @deffn {Scheme Procedure} getlogin
1145 @deffnx {C Function} scm_getlogin ()
1146 Return a string containing the name of the user logged in on
1147 the controlling terminal of the process, or @code{#f} if this
1148 information cannot be obtained.
1156 @deffn {Scheme Procedure} current-time
1157 @deffnx {C Function} scm_current_time ()
1158 Return the number of seconds since 1970-01-01 00:00:00 @acronym{UTC},
1159 excluding leap seconds.
1162 @deffn {Scheme Procedure} gettimeofday
1163 @deffnx {C Function} scm_gettimeofday ()
1164 Return a pair containing the number of seconds and microseconds
1165 since 1970-01-01 00:00:00 @acronym{UTC}, excluding leap seconds. Note:
1166 whether true microsecond resolution is available depends on the
1170 The following procedures either accept an object representing a broken down
1171 time and return a selected component, or accept an object representing
1172 a broken down time and a value and set the component to the value.
1173 The numbers in parentheses give the usual range.
1175 @deffn {Scheme Procedure} tm:sec tm
1176 @deffnx {Scheme Procedure} set-tm:sec tm val
1179 @deffn {Scheme Procedure} tm:min tm
1180 @deffnx {Scheme Procedure} set-tm:min tm val
1183 @deffn {Scheme Procedure} tm:hour tm
1184 @deffnx {Scheme Procedure} set-tm:hour tm val
1187 @deffn {Scheme Procedure} tm:mday tm
1188 @deffnx {Scheme Procedure} set-tm:mday tm val
1189 Day of the month (1-31).
1191 @deffn {Scheme Procedure} tm:mon tm
1192 @deffnx {Scheme Procedure} set-tm:mon tm val
1195 @deffn {Scheme Procedure} tm:year tm
1196 @deffnx {Scheme Procedure} set-tm:year tm val
1197 Year (70-), the year minus 1900.
1199 @deffn {Scheme Procedure} tm:wday tm
1200 @deffnx {Scheme Procedure} set-tm:wday tm val
1201 Day of the week (0-6) with Sunday represented as 0.
1203 @deffn {Scheme Procedure} tm:yday tm
1204 @deffnx {Scheme Procedure} set-tm:yday tm val
1205 Day of the year (0-364, 365 in leap years).
1207 @deffn {Scheme Procedure} tm:isdst tm
1208 @deffnx {Scheme Procedure} set-tm:isdst tm val
1209 Daylight saving indicator (0 for ``no'', greater than 0 for ``yes'', less than
1212 @deffn {Scheme Procedure} tm:gmtoff tm
1213 @deffnx {Scheme Procedure} set-tm:gmtoff tm val
1214 Time zone offset in seconds west of @acronym{UTC} (-46800 to 43200).
1215 For example on East coast USA (zone @samp{EST+5}) this would be 18000
1216 (ie.@: @m{5\times60\times60,5*60*60}) in winter, or 14400
1217 (ie.@: @m{4\times60\times60,4*60*60}) during daylight savings.
1219 Note @code{tm:gmtoff} is not the same as @code{tm_gmtoff} in the C
1220 @code{tm} structure. @code{tm_gmtoff} is seconds east and hence the
1221 negative of the value here.
1223 @deffn {Scheme Procedure} tm:zone tm
1224 @deffnx {Scheme Procedure} set-tm:zone tm val
1225 Time zone label (a string), not necessarily unique.
1229 @deffn {Scheme Procedure} localtime time [zone]
1230 @deffnx {C Function} scm_localtime (time, zone)
1232 Return an object representing the broken down components of
1233 @var{time}, an integer like the one returned by
1234 @code{current-time}. The time zone for the calculation is
1235 optionally specified by @var{zone} (a string), otherwise the
1236 @env{TZ} environment variable or the system default is used.
1239 @deffn {Scheme Procedure} gmtime time
1240 @deffnx {C Function} scm_gmtime (time)
1241 Return an object representing the broken down components of
1242 @var{time}, an integer like the one returned by
1243 @code{current-time}. The values are calculated for @acronym{UTC}.
1246 @deffn {Scheme Procedure} mktime sbd-time [zone]
1247 @deffnx {C Function} scm_mktime (sbd_time, zone)
1248 For a broken down time object @var{sbd-time}, return a pair the
1249 @code{car} of which is an integer time like @code{current-time}, and
1250 the @code{cdr} of which is a new broken down time with normalized
1253 @var{zone} is a timezone string, or the default is the @env{TZ}
1254 environment variable or the system default (@pxref{TZ Variable,,
1255 Specifying the Time Zone with @env{TZ}, libc, GNU C Library Reference
1256 Manual}). @var{sbd-time} is taken to be in that @var{zone}.
1258 The following fields of @var{sbd-time} are used: @code{tm:year},
1259 @code{tm:mon}, @code{tm:mday}, @code{tm:hour}, @code{tm:min},
1260 @code{tm:sec}, @code{tm:isdst}. The values can be outside their usual
1261 ranges. For example @code{tm:hour} normally goes up to 23, but a
1262 value say 33 would mean 9 the following day.
1264 @code{tm:isdst} in @var{sbd-time} says whether the time given is with
1265 daylight savings or not. This is ignored if @var{zone} doesn't have
1266 any daylight savings adjustment amount.
1268 The broken down time in the return normalizes the values of
1269 @var{sbd-time} by bringing them into their usual ranges, and using the
1270 actual daylight savings rule for that time in @var{zone} (which may
1271 differ from what @var{sbd-time} had). The easiest way to think of
1272 this is that @var{sbd-time} plus @var{zone} converts to the integer
1273 UTC time, then a @code{localtime} is applied to get the normal
1274 presentation of that time, in @var{zone}.
1277 @deffn {Scheme Procedure} tzset
1278 @deffnx {C Function} scm_tzset ()
1279 Initialize the timezone from the @env{TZ} environment variable
1280 or the system default. It's not usually necessary to call this procedure
1281 since it's done automatically by other procedures that depend on the
1285 @deffn {Scheme Procedure} strftime format tm
1286 @deffnx {C Function} scm_strftime (format, tm)
1287 @cindex time formatting
1288 Return a string which is broken-down time structure @var{tm} formatted
1289 according to the given @var{format} string.
1291 @var{format} contains field specifications introduced by a @samp{%}
1292 character. See @ref{Formatting Calendar Time,,, libc, The GNU C
1293 Library Reference Manual}, or @samp{man 3 strftime}, for the available
1297 (strftime "%c" (localtime (current-time)))
1298 @result{} "Mon Mar 11 20:17:43 2002"
1301 If @code{setlocale} has been called (@pxref{Locales}), month and day
1302 names are from the current locale and in the locale character set.
1305 @deffn {Scheme Procedure} strptime format string
1306 @deffnx {C Function} scm_strptime (format, string)
1307 @cindex time parsing
1308 Performs the reverse action to @code{strftime}, parsing
1309 @var{string} according to the specification supplied in
1310 @var{format}. The interpretation of month and day names is
1311 dependent on the current locale. The value returned is a pair.
1312 The @acronym{CAR} has an object with time components
1313 in the form returned by @code{localtime} or @code{gmtime},
1314 but the time zone components
1315 are not usefully set.
1316 The @acronym{CDR} reports the number of characters from @var{string}
1317 which were used for the conversion.
1320 @defvar internal-time-units-per-second
1321 The value of this variable is the number of time units per second
1322 reported by the following procedures.
1325 @deffn {Scheme Procedure} times
1326 @deffnx {C Function} scm_times ()
1327 Return an object with information about real and processor
1328 time. The following procedures accept such an object as an
1329 argument and return a selected component:
1331 @deffn {Scheme Procedure} tms:clock tms
1332 The current real time, expressed as time units relative to an
1335 @deffn {Scheme Procedure} tms:utime tms
1336 The CPU time units used by the calling process.
1338 @deffn {Scheme Procedure} tms:stime tms
1339 The CPU time units used by the system on behalf of the calling
1342 @deffn {Scheme Procedure} tms:cutime tms
1343 The CPU time units used by terminated child processes of the
1344 calling process, whose status has been collected (e.g., using
1347 @deffn {Scheme Procedure} tms:cstime tms
1348 Similarly, the CPU times units used by the system on behalf of
1349 terminated child processes.
1353 @deffn {Scheme Procedure} get-internal-real-time
1354 @deffnx {C Function} scm_get_internal_real_time ()
1355 Return the number of time units since the interpreter was
1359 @deffn {Scheme Procedure} get-internal-run-time
1360 @deffnx {C Function} scm_get_internal_run_time ()
1361 Return the number of time units of processor time used by the
1362 interpreter. Both @emph{system} and @emph{user} time are
1363 included but subprocesses are not.
1366 @node Runtime Environment
1367 @subsection Runtime Environment
1369 @deffn {Scheme Procedure} program-arguments
1370 @deffnx {Scheme Procedure} command-line
1371 @deffnx {Scheme Procedure} set-program-arguments
1372 @deffnx {C Function} scm_program_arguments ()
1373 @deffnx {C Function} scm_set_program_arguments_scm (lst)
1374 @cindex command line
1375 @cindex program arguments
1376 Get the command line arguments passed to Guile, or set new arguments.
1378 The arguments are a list of strings, the first of which is the invoked
1379 program name. This is just @nicode{"guile"} (or the executable path)
1380 when run interactively, or it's the script name when running a script
1381 with @option{-s} (@pxref{Invoking Guile}).
1384 guile -L /my/extra/dir -s foo.scm abc def
1386 (program-arguments) @result{} ("foo.scm" "abc" "def")
1389 @code{set-program-arguments} allows a library module or similar to
1390 modify the arguments, for example to strip options it recognises,
1391 leaving the rest for the mainline.
1393 The argument list is held in a fluid, which means it's separate for
1394 each thread. Neither the list nor the strings within it are copied at
1395 any point and normally should not be mutated.
1397 The two names @code{program-arguments} and @code{command-line} are an
1398 historical accident, they both do exactly the same thing. The name
1399 @code{scm_set_program_arguments_scm} has an extra @code{_scm} on the
1400 end to avoid clashing with the C function below.
1403 @deftypefn {C Function} void scm_set_program_arguments (int argc, char **argv, char *first)
1404 @cindex command line
1405 @cindex program arguments
1406 Set the list of command line arguments for @code{program-arguments}
1407 and @code{command-line} above.
1409 @var{argv} is an array of null-terminated strings, as in a C
1410 @code{main} function. @var{argc} is the number of strings in
1411 @var{argv}, or if it's negative then a @code{NULL} in @var{argv} marks
1414 @var{first} is an extra string put at the start of the arguments, or
1415 @code{NULL} for no such extra. This is a convenient way to pass the
1416 program name after advancing @var{argv} to strip option arguments.
1421 char *progname = argv[0];
1422 for (argv++; argv[0] != NULL && argv[0][0] == '-'; argv++)
1424 /* munch option ... */
1426 /* remaining args for scheme level use */
1427 scm_set_program_arguments (-1, argv, progname);
1431 This sort of thing is often done at startup under
1432 @code{scm_boot_guile} with options handled at the C level removed.
1433 The given strings are all copied, so the C data is not accessed again
1434 once @code{scm_set_program_arguments} returns.
1437 @deffn {Scheme Procedure} getenv name
1438 @deffnx {C Function} scm_getenv (name)
1440 Looks up the string @var{name} in the current environment. The return
1441 value is @code{#f} unless a string of the form @code{NAME=VALUE} is
1442 found, in which case the string @code{VALUE} is returned.
1445 @deffn {Scheme Procedure} setenv name value
1446 Modifies the environment of the current process, which is
1447 also the default environment inherited by child processes.
1449 If @var{value} is @code{#f}, then @var{name} is removed from the
1450 environment. Otherwise, the string @var{name}=@var{value} is added
1451 to the environment, replacing any existing string with name matching
1454 The return value is unspecified.
1457 @deffn {Scheme Procedure} unsetenv name
1458 Remove variable @var{name} from the environment. The
1459 name can not contain a @samp{=} character.
1462 @deffn {Scheme Procedure} environ [env]
1463 @deffnx {C Function} scm_environ (env)
1464 If @var{env} is omitted, return the current environment (in the
1465 Unix sense) as a list of strings. Otherwise set the current
1466 environment, which is also the default environment for child
1467 processes, to the supplied list of strings. Each member of
1468 @var{env} should be of the form @var{name}=@var{value} and values of
1469 @var{name} should not be duplicated. If @var{env} is supplied
1470 then the return value is unspecified.
1473 @deffn {Scheme Procedure} putenv str
1474 @deffnx {C Function} scm_putenv (str)
1475 Modifies the environment of the current process, which is
1476 also the default environment inherited by child processes.
1478 If @var{str} is of the form @code{NAME=VALUE} then it will be written
1479 directly into the environment, replacing any existing environment string
1481 name matching @code{NAME}. If @var{str} does not contain an equal
1482 sign, then any existing string with name matching @var{str} will
1485 The return value is unspecified.
1490 @subsection Processes
1492 @cindex child processes
1495 @deffn {Scheme Procedure} chdir str
1496 @deffnx {C Function} scm_chdir (str)
1497 @cindex current directory
1498 Change the current working directory to @var{str}.
1499 The return value is unspecified.
1503 @deffn {Scheme Procedure} getcwd
1504 @deffnx {C Function} scm_getcwd ()
1505 Return the name of the current working directory.
1508 @deffn {Scheme Procedure} umask [mode]
1509 @deffnx {C Function} scm_umask (mode)
1510 If @var{mode} is omitted, returns a decimal number representing the
1511 current file creation mask. Otherwise the file creation mask is set
1512 to @var{mode} and the previous value is returned. @xref{Setting
1513 Permissions,,Assigning File Permissions,libc,The GNU C Library
1514 Reference Manual}, for more on how to use umasks.
1516 E.g., @code{(umask #o022)} sets the mask to octal 22/decimal 18.
1519 @deffn {Scheme Procedure} chroot path
1520 @deffnx {C Function} scm_chroot (path)
1521 Change the root directory to that specified in @var{path}.
1522 This directory will be used for path names beginning with
1523 @file{/}. The root directory is inherited by all children
1524 of the current process. Only the superuser may change the
1528 @deffn {Scheme Procedure} getpid
1529 @deffnx {C Function} scm_getpid ()
1530 Return an integer representing the current process ID.
1533 @deffn {Scheme Procedure} getgroups
1534 @deffnx {C Function} scm_getgroups ()
1535 Return a vector of integers representing the current
1536 supplementary group IDs.
1539 @deffn {Scheme Procedure} getppid
1540 @deffnx {C Function} scm_getppid ()
1541 Return an integer representing the process ID of the parent
1545 @deffn {Scheme Procedure} getuid
1546 @deffnx {C Function} scm_getuid ()
1547 Return an integer representing the current real user ID.
1550 @deffn {Scheme Procedure} getgid
1551 @deffnx {C Function} scm_getgid ()
1552 Return an integer representing the current real group ID.
1555 @deffn {Scheme Procedure} geteuid
1556 @deffnx {C Function} scm_geteuid ()
1557 Return an integer representing the current effective user ID.
1558 If the system does not support effective IDs, then the real ID
1559 is returned. @code{(provided? 'EIDs)} reports whether the
1560 system supports effective IDs.
1563 @deffn {Scheme Procedure} getegid
1564 @deffnx {C Function} scm_getegid ()
1565 Return an integer representing the current effective group ID.
1566 If the system does not support effective IDs, then the real ID
1567 is returned. @code{(provided? 'EIDs)} reports whether the
1568 system supports effective IDs.
1571 @deffn {Scheme Procedure} setgroups vec
1572 @deffnx {C Function} scm_setgroups (vec)
1573 Set the current set of supplementary group IDs to the integers in the
1574 given vector @var{vec}. The return value is unspecified.
1576 Generally only the superuser can set the process group IDs
1577 (@pxref{Setting Groups, Setting the Group IDs,, libc, The GNU C
1578 Library Reference Manual}).
1581 @deffn {Scheme Procedure} setuid id
1582 @deffnx {C Function} scm_setuid (id)
1583 Sets both the real and effective user IDs to the integer @var{id}, provided
1584 the process has appropriate privileges.
1585 The return value is unspecified.
1588 @deffn {Scheme Procedure} setgid id
1589 @deffnx {C Function} scm_setgid (id)
1590 Sets both the real and effective group IDs to the integer @var{id}, provided
1591 the process has appropriate privileges.
1592 The return value is unspecified.
1595 @deffn {Scheme Procedure} seteuid id
1596 @deffnx {C Function} scm_seteuid (id)
1597 Sets the effective user ID to the integer @var{id}, provided the process
1598 has appropriate privileges. If effective IDs are not supported, the
1599 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1600 system supports effective IDs.
1601 The return value is unspecified.
1604 @deffn {Scheme Procedure} setegid id
1605 @deffnx {C Function} scm_setegid (id)
1606 Sets the effective group ID to the integer @var{id}, provided the process
1607 has appropriate privileges. If effective IDs are not supported, the
1608 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1609 system supports effective IDs.
1610 The return value is unspecified.
1613 @deffn {Scheme Procedure} getpgrp
1614 @deffnx {C Function} scm_getpgrp ()
1615 Return an integer representing the current process group ID.
1616 This is the @acronym{POSIX} definition, not @acronym{BSD}.
1619 @deffn {Scheme Procedure} setpgid pid pgid
1620 @deffnx {C Function} scm_setpgid (pid, pgid)
1621 Move the process @var{pid} into the process group @var{pgid}. @var{pid} or
1622 @var{pgid} must be integers: they can be zero to indicate the ID of the
1624 Fails on systems that do not support job control.
1625 The return value is unspecified.
1628 @deffn {Scheme Procedure} setsid
1629 @deffnx {C Function} scm_setsid ()
1630 Creates a new session. The current process becomes the session leader
1631 and is put in a new process group. The process will be detached
1632 from its controlling terminal if it has one.
1633 The return value is an integer representing the new process group ID.
1636 @deffn {Scheme Procedure} getsid pid
1637 @deffnx {C Function} scm_getsid (pid)
1638 Returns the session ID of process @var{pid}. (The session
1639 ID of a process is the process group ID of its session leader.)
1642 @deffn {Scheme Procedure} waitpid pid [options]
1643 @deffnx {C Function} scm_waitpid (pid, options)
1644 This procedure collects status information from a child process which
1645 has terminated or (optionally) stopped. Normally it will
1646 suspend the calling process until this can be done. If more than one
1647 child process is eligible then one will be chosen by the operating system.
1649 The value of @var{pid} determines the behaviour:
1652 @item @var{pid} greater than 0
1653 Request status information from the specified child process.
1654 @item @var{pid} equal to -1 or @code{WAIT_ANY}
1656 Request status information for any child process.
1657 @item @var{pid} equal to 0 or @code{WAIT_MYPGRP}
1659 Request status information for any child process in the current process
1661 @item @var{pid} less than -1
1662 Request status information for any child process whose process group ID
1663 is @minus{}@var{pid}.
1666 The @var{options} argument, if supplied, should be the bitwise OR of the
1667 values of zero or more of the following variables:
1670 Return immediately even if there are no child processes to be collected.
1674 Report status information for stopped processes as well as terminated
1678 The return value is a pair containing:
1682 The process ID of the child process, or 0 if @code{WNOHANG} was
1683 specified and no process was collected.
1685 The integer status value.
1690 functions can be used to decode the process status code returned
1693 @deffn {Scheme Procedure} status:exit-val status
1694 @deffnx {C Function} scm_status_exit_val (status)
1695 Return the exit status value, as would be set if a process
1696 ended normally through a call to @code{exit} or @code{_exit},
1697 if any, otherwise @code{#f}.
1700 @deffn {Scheme Procedure} status:term-sig status
1701 @deffnx {C Function} scm_status_term_sig (status)
1702 Return the signal number which terminated the process, if any,
1703 otherwise @code{#f}.
1706 @deffn {Scheme Procedure} status:stop-sig status
1707 @deffnx {C Function} scm_status_stop_sig (status)
1708 Return the signal number which stopped the process, if any,
1709 otherwise @code{#f}.
1712 @deffn {Scheme Procedure} system [cmd]
1713 @deffnx {C Function} scm_system (cmd)
1714 Execute @var{cmd} using the operating system's ``command
1715 processor''. Under Unix this is usually the default shell
1716 @code{sh}. The value returned is @var{cmd}'s exit status as
1717 returned by @code{waitpid}, which can be interpreted using the
1720 If @code{system} is called without arguments, return a boolean
1721 indicating whether the command processor is available.
1724 @deffn {Scheme Procedure} system* arg1 arg2 @dots{}
1725 @deffnx {C Function} scm_system_star (args)
1726 Execute the command indicated by @var{arg1} @var{arg2} @enddots{}. The
1727 first element must be a string indicating the command to be executed,
1728 and the remaining items must be strings representing each of the
1729 arguments to that command.
1731 This function returns the exit status of the command as provided by
1732 @code{waitpid}. This value can be handled with @code{status:exit-val}
1733 and the related functions.
1735 @code{system*} is similar to @code{system}, but accepts only one
1736 string per-argument, and performs no shell interpretation. The
1737 command is executed using fork and execlp. Accordingly this function
1738 may be safer than @code{system} in situations where shell
1739 interpretation is not required.
1741 Example: (system* "echo" "foo" "bar")
1744 @deffn {Scheme Procedure} quit [status]
1745 @deffnx {Scheme Procedure} exit [status]
1746 Terminate the current process with proper unwinding of the Scheme stack.
1747 The exit status zero if @var{status} is not supplied. If @var{status}
1748 is supplied, and it is an integer, that integer is used as the exit
1749 status. If @var{status} is @code{#t} or @code{#f}, the exit status is 0
1752 The procedure @code{exit} is an alias of @code{quit}. They have the
1756 @deffn {Scheme Procedure} primitive-exit [status]
1757 @deffnx {Scheme Procedure} primitive-_exit [status]
1758 @deffnx {C Function} scm_primitive_exit (status)
1759 @deffnx {C Function} scm_primitive__exit (status)
1760 Terminate the current process without unwinding the Scheme stack. The
1761 exit status is @var{status} if supplied, otherwise zero.
1763 @code{primitive-exit} uses the C @code{exit} function and hence runs
1764 usual C level cleanups (flush output streams, call @code{atexit}
1765 functions, etc, see @ref{Normal Termination,,, libc, The GNU C Library
1766 Reference Manual})).
1768 @code{primitive-_exit} is the @code{_exit} system call
1769 (@pxref{Termination Internals,,, libc, The GNU C Library Reference
1770 Manual}). This terminates the program immediately, with neither
1771 Scheme-level nor C-level cleanups.
1773 The typical use for @code{primitive-_exit} is from a child process
1774 created with @code{primitive-fork}. For example in a Gdk program the
1775 child process inherits the X server connection and a C-level
1776 @code{atexit} cleanup which will close that connection. But closing
1777 in the child would upset the protocol in the parent, so
1778 @code{primitive-_exit} should be used to exit without that.
1781 @deffn {Scheme Procedure} execl filename arg @dots{}
1782 @deffnx {C Function} scm_execl (filename, args)
1783 Executes the file named by @var{filename} as a new process image.
1784 The remaining arguments are supplied to the process; from a C program
1785 they are accessible as the @code{argv} argument to @code{main}.
1786 Conventionally the first @var{arg} is the same as @var{filename}.
1787 All arguments must be strings.
1789 If @var{arg} is missing, @var{filename} is executed with a null
1790 argument list, which may have system-dependent side-effects.
1792 This procedure is currently implemented using the @code{execv} system
1793 call, but we call it @code{execl} because of its Scheme calling interface.
1796 @deffn {Scheme Procedure} execlp filename arg @dots{}
1797 @deffnx {C Function} scm_execlp (filename, args)
1798 Similar to @code{execl}, however if
1799 @var{filename} does not contain a slash
1800 then the file to execute will be located by searching the
1801 directories listed in the @code{PATH} environment variable.
1803 This procedure is currently implemented using the @code{execvp} system
1804 call, but we call it @code{execlp} because of its Scheme calling interface.
1807 @deffn {Scheme Procedure} execle filename env arg @dots{}
1808 @deffnx {C Function} scm_execle (filename, env, args)
1809 Similar to @code{execl}, but the environment of the new process is
1810 specified by @var{env}, which must be a list of strings as returned by the
1811 @code{environ} procedure.
1813 This procedure is currently implemented using the @code{execve} system
1814 call, but we call it @code{execle} because of its Scheme calling interface.
1817 @deffn {Scheme Procedure} primitive-fork
1818 @deffnx {C Function} scm_fork ()
1819 Creates a new ``child'' process by duplicating the current ``parent'' process.
1820 In the child the return value is 0. In the parent the return value is
1821 the integer process ID of the child.
1823 Note that it is unsafe to fork a process that has multiple threads
1824 running, as only the thread that calls @code{primitive-fork} will
1825 persist in the child. Any resources that other threads held, such as
1826 locked mutexes or open file descriptors, are lost. Indeed, @acronym{POSIX}
1827 specifies that only async-signal-safe procedures are safe to call after
1828 a multithreaded fork, which is a very limited set. Guile issues a
1829 warning if it detects a fork from a multi-threaded program.
1831 If you are going to @code{exec} soon after forking, the procedures in
1832 @code{(ice-9 popen)} may be useful to you, as they fork and exec within
1833 an async-signal-safe function carefully written to ensure robust program
1834 behavior, even in the presence of threads. @xref{Pipes}, for more.
1836 This procedure has been renamed from @code{fork} to avoid a naming conflict
1840 @deffn {Scheme Procedure} nice incr
1841 @deffnx {C Function} scm_nice (incr)
1842 @cindex process priority
1843 Increment the priority of the current process by @var{incr}. A higher
1844 priority value means that the process runs less often.
1845 The return value is unspecified.
1848 @deffn {Scheme Procedure} setpriority which who prio
1849 @deffnx {C Function} scm_setpriority (which, who, prio)
1850 @vindex PRIO_PROCESS
1853 Set the scheduling priority of the process, process group
1854 or user, as indicated by @var{which} and @var{who}. @var{which}
1855 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1856 or @code{PRIO_USER}, and @var{who} is interpreted relative to
1857 @var{which} (a process identifier for @code{PRIO_PROCESS},
1858 process group identifier for @code{PRIO_PGRP}, and a user
1859 identifier for @code{PRIO_USER}. A zero value of @var{who}
1860 denotes the current process, process group, or user.
1861 @var{prio} is a value in the range [@minus{}20,20]. The default
1862 priority is 0; lower priorities (in numerical terms) cause more
1863 favorable scheduling. Sets the priority of all of the specified
1864 processes. Only the super-user may lower priorities. The return
1865 value is not specified.
1868 @deffn {Scheme Procedure} getpriority which who
1869 @deffnx {C Function} scm_getpriority (which, who)
1870 @vindex PRIO_PROCESS
1873 Return the scheduling priority of the process, process group
1874 or user, as indicated by @var{which} and @var{who}. @var{which}
1875 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1876 or @code{PRIO_USER}, and @var{who} should be interpreted depending on
1877 @var{which} (a process identifier for @code{PRIO_PROCESS},
1878 process group identifier for @code{PRIO_PGRP}, and a user
1879 identifier for @code{PRIO_USER}). A zero value of @var{who}
1880 denotes the current process, process group, or user. Return
1881 the highest priority (lowest numerical value) of any of the
1882 specified processes.
1885 @cindex affinity, CPU
1887 @deffn {Scheme Procedure} getaffinity pid
1888 @deffnx {C Function} scm_getaffinity (pid)
1889 Return a bitvector representing the CPU affinity mask for
1890 process @var{pid}. Each CPU the process has affinity with
1891 has its corresponding bit set in the returned bitvector.
1892 The number of bits set is a good estimate of how many CPUs
1893 Guile can use without stepping on other processes' toes.
1895 Currently this procedure is only defined on GNU variants
1896 (@pxref{CPU Affinity, @code{sched_getaffinity},, libc, The
1897 GNU C Library Reference Manual}).
1900 @deffn {Scheme Procedure} setaffinity pid mask
1901 @deffnx {C Function} scm_setaffinity (pid, mask)
1902 Install the CPU affinity mask @var{mask}, a bitvector, for
1903 the process or thread with ID @var{pid}. The return value
1906 Currently this procedure is only defined on GNU variants
1907 (@pxref{CPU Affinity, @code{sched_setaffinity},, libc, The
1908 GNU C Library Reference Manual}).
1911 @deffn {Scheme Procedure} total-processor-count
1912 @deffnx {C Function} scm_total_processor_count ()
1913 Return the total number of processors of the machine, which
1914 is guaranteed to be at least 1. A ``processor'' here is a
1915 thread execution unit, which can be either:
1918 @item an execution core in a (possibly multi-core) chip, in a
1919 (possibly multi- chip) module, in a single computer, or
1920 @item a thread execution unit inside a core in the case of
1921 @dfn{hyper-threaded} CPUs.
1924 Which of the two definitions is used, is unspecified.
1927 @deffn {Scheme Procedure} current-processor-count
1928 @deffnx {C Function} scm_current_processor_count ()
1929 Like @code{total-processor-count}, but return the number of
1930 processors available to the current process. See
1931 @code{setaffinity} and @code{getaffinity} for more
1940 The following procedures raise, handle and wait for signals.
1942 Scheme code signal handlers are run via a system async (@pxref{System
1943 asyncs}), so they're called in the handler's thread at the next safe
1944 opportunity. Generally this is after any currently executing
1945 primitive procedure finishes (which could be a long time for
1946 primitives that wait for an external event).
1948 @deffn {Scheme Procedure} kill pid sig
1949 @deffnx {C Function} scm_kill (pid, sig)
1950 Sends a signal to the specified process or group of processes.
1952 @var{pid} specifies the processes to which the signal is sent:
1955 @item @var{pid} greater than 0
1956 The process whose identifier is @var{pid}.
1957 @item @var{pid} equal to 0
1958 All processes in the current process group.
1959 @item @var{pid} less than -1
1960 The process group whose identifier is -@var{pid}
1961 @item @var{pid} equal to -1
1962 If the process is privileged, all processes except for some special
1963 system processes. Otherwise, all processes with the current effective
1967 @var{sig} should be specified using a variable corresponding to
1968 the Unix symbolic name, e.g.,
1978 A full list of signals on the GNU system may be found in @ref{Standard
1979 Signals,,,libc,The GNU C Library Reference Manual}.
1982 @deffn {Scheme Procedure} raise sig
1983 @deffnx {C Function} scm_raise (sig)
1984 Sends a specified signal @var{sig} to the current process, where
1985 @var{sig} is as described for the @code{kill} procedure.
1988 @deffn {Scheme Procedure} sigaction signum [handler [flags [thread]]]
1989 @deffnx {C Function} scm_sigaction (signum, handler, flags)
1990 @deffnx {C Function} scm_sigaction_for_thread (signum, handler, flags, thread)
1991 Install or report the signal handler for a specified signal.
1993 @var{signum} is the signal number, which can be specified using the value
1994 of variables such as @code{SIGINT}.
1996 If @var{handler} is omitted, @code{sigaction} returns a pair: the
1997 @acronym{CAR} is the current signal hander, which will be either an
1998 integer with the value @code{SIG_DFL} (default action) or
1999 @code{SIG_IGN} (ignore), or the Scheme procedure which handles the
2000 signal, or @code{#f} if a non-Scheme procedure handles the signal.
2001 The @acronym{CDR} contains the current @code{sigaction} flags for the
2004 If @var{handler} is provided, it is installed as the new handler for
2005 @var{signum}. @var{handler} can be a Scheme procedure taking one
2006 argument, or the value of @code{SIG_DFL} (default action) or
2007 @code{SIG_IGN} (ignore), or @code{#f} to restore whatever signal handler
2008 was installed before @code{sigaction} was first used. When a scheme
2009 procedure has been specified, that procedure will run in the given
2010 @var{thread}. When no thread has been given, the thread that made this
2011 call to @code{sigaction} is used.
2013 @var{flags} is a @code{logior} (@pxref{Bitwise Operations}) of the
2014 following (where provided by the system), or @code{0} for none.
2016 @defvar SA_NOCLDSTOP
2017 By default, @code{SIGCHLD} is signalled when a child process stops
2018 (ie.@: receives @code{SIGSTOP}), and when a child process terminates.
2019 With the @code{SA_NOCLDSTOP} flag, @code{SIGCHLD} is only signalled
2020 for termination, not stopping.
2022 @code{SA_NOCLDSTOP} has no effect on signals other than
2027 If a signal occurs while in a system call, deliver the signal then
2028 restart the system call (as opposed to returning an @code{EINTR} error
2032 The return value is a pair with information about the old handler as
2035 This interface does not provide access to the ``signal blocking''
2036 facility. Maybe this is not needed, since the thread support may
2037 provide solutions to the problem of consistent access to data
2041 @deffn {Scheme Procedure} restore-signals
2042 @deffnx {C Function} scm_restore_signals ()
2043 Return all signal handlers to the values they had before any call to
2044 @code{sigaction} was made. The return value is unspecified.
2047 @deffn {Scheme Procedure} alarm i
2048 @deffnx {C Function} scm_alarm (i)
2049 Set a timer to raise a @code{SIGALRM} signal after the specified
2050 number of seconds (an integer). It's advisable to install a signal
2052 @code{SIGALRM} beforehand, since the default action is to terminate
2055 The return value indicates the time remaining for the previous alarm,
2056 if any. The new value replaces the previous alarm. If there was
2057 no previous alarm, the return value is zero.
2060 @deffn {Scheme Procedure} pause
2061 @deffnx {C Function} scm_pause ()
2062 Pause the current process (thread?) until a signal arrives whose
2063 action is to either terminate the current process or invoke a
2064 handler procedure. The return value is unspecified.
2067 @deffn {Scheme Procedure} sleep secs
2068 @deffnx {Scheme Procedure} usleep usecs
2069 @deffnx {C Function} scm_sleep (secs)
2070 @deffnx {C Function} scm_usleep (usecs)
2071 Wait the given period @var{secs} seconds or @var{usecs} microseconds
2072 (both integers). If a signal arrives the wait stops and the return
2073 value is the time remaining, in seconds or microseconds respectively.
2074 If the period elapses with no signal the return is zero.
2076 On most systems the process scheduler is not microsecond accurate and
2077 the actual period slept by @code{usleep} might be rounded to a system
2078 clock tick boundary, which might be 10 milliseconds for instance.
2080 See @code{scm_std_sleep} and @code{scm_std_usleep} for equivalents at
2081 the C level (@pxref{Blocking}).
2084 @deffn {Scheme Procedure} getitimer which_timer
2085 @deffnx {Scheme Procedure} setitimer which_timer interval_seconds interval_microseconds periodic_seconds periodic_microseconds
2086 @deffnx {C Function} scm_getitimer (which_timer)
2087 @deffnx {C Function} scm_setitimer (which_timer, interval_seconds, interval_microseconds, periodic_seconds, periodic_microseconds)
2088 Get or set the periods programmed in certain system timers. These
2089 timers have a current interval value which counts down and on reaching
2090 zero raises a signal. An optional periodic value can be set to
2091 restart from there each time, for periodic operation.
2092 @var{which_timer} is one of the following values
2095 A real-time timer, counting down elapsed real time. At zero it raises
2096 @code{SIGALRM}. This is like @code{alarm} above, but with a higher
2100 @defvar ITIMER_VIRTUAL
2101 A virtual-time timer, counting down while the current process is
2102 actually using CPU. At zero it raises @code{SIGVTALRM}.
2106 A profiling timer, counting down while the process is running (like
2107 @code{ITIMER_VIRTUAL}) and also while system calls are running on the
2108 process's behalf. At zero it raises a @code{SIGPROF}.
2110 This timer is intended for profiling where a program is spending its
2111 time (by looking where it is when the timer goes off).
2114 @code{getitimer} returns the current timer value and its programmed
2115 restart value, as a list containing two pairs. Each pair is a time in
2116 seconds and microseconds: @code{((@var{interval_secs}
2117 . @var{interval_usecs}) (@var{periodic_secs}
2118 . @var{periodic_usecs}))}.
2120 @code{setitimer} sets the timer values similarly, in seconds and
2121 microseconds (which must be integers). The periodic value can be zero
2122 to have the timer run down just once. The return value is the timer's
2123 previous setting, in the same form as @code{getitimer} returns.
2126 (setitimer ITIMER_REAL
2127 5 500000 ;; first SIGALRM in 5.5 seconds time
2128 2 0) ;; then repeat every 2 seconds
2131 Although the timers are programmed in microseconds, the actual
2132 accuracy might not be that high.
2136 @node Terminals and Ptys
2137 @subsection Terminals and Ptys
2139 @deffn {Scheme Procedure} isatty? port
2140 @deffnx {C Function} scm_isatty_p (port)
2142 Return @code{#t} if @var{port} is using a serial non--file
2143 device, otherwise @code{#f}.
2146 @deffn {Scheme Procedure} ttyname port
2147 @deffnx {C Function} scm_ttyname (port)
2149 Return a string with the name of the serial terminal device
2150 underlying @var{port}.
2153 @deffn {Scheme Procedure} ctermid
2154 @deffnx {C Function} scm_ctermid ()
2156 Return a string containing the file name of the controlling
2157 terminal for the current process.
2160 @deffn {Scheme Procedure} tcgetpgrp port
2161 @deffnx {C Function} scm_tcgetpgrp (port)
2162 @cindex process group
2163 Return the process group ID of the foreground process group
2164 associated with the terminal open on the file descriptor
2165 underlying @var{port}.
2167 If there is no foreground process group, the return value is a
2168 number greater than 1 that does not match the process group ID
2169 of any existing process group. This can happen if all of the
2170 processes in the job that was formerly the foreground job have
2171 terminated, and no other job has yet been moved into the
2175 @deffn {Scheme Procedure} tcsetpgrp port pgid
2176 @deffnx {C Function} scm_tcsetpgrp (port, pgid)
2177 @cindex process group
2178 Set the foreground process group ID for the terminal used by the file
2179 descriptor underlying @var{port} to the integer @var{pgid}.
2181 must be a member of the same session as @var{pgid} and must have the same
2182 controlling terminal. The return value is unspecified.
2189 The following procedures are similar to the @code{popen} and
2190 @code{pclose} system routines. The code is in a separate ``popen''
2191 module@footnote{This module is only available on systems where the
2192 @code{fork} feature is provided (@pxref{Common Feature Symbols}).}:
2195 (use-modules (ice-9 popen))
2199 @deffn {Scheme Procedure} open-pipe command mode
2200 @deffnx {Scheme Procedure} open-pipe* mode prog [args...]
2201 Execute a command in a subprocess, with a pipe to it or from it, or
2202 with pipes in both directions.
2204 @code{open-pipe} runs the shell @var{command} using @samp{/bin/sh -c}.
2205 @code{open-pipe*} executes @var{prog} directly, with the optional
2206 @var{args} arguments (all strings).
2208 @var{mode} should be one of the following values. @code{OPEN_READ} is
2209 an input pipe, ie.@: to read from the subprocess. @code{OPEN_WRITE}
2210 is an output pipe, ie.@: to write to it.
2217 For an input pipe, the child's standard output is the pipe and
2218 standard input is inherited from @code{current-input-port}. For an
2219 output pipe, the child's standard input is the pipe and standard
2220 output is inherited from @code{current-output-port}. In all cases
2221 cases the child's standard error is inherited from
2222 @code{current-error-port} (@pxref{Default Ports}).
2224 If those @code{current-X-ports} are not files of some kind, and hence
2225 don't have file descriptors for the child, then @file{/dev/null} is
2228 Care should be taken with @code{OPEN_BOTH}, a deadlock will occur if
2229 both parent and child are writing, and waiting until the write
2230 completes before doing any reading. Each direction has
2231 @code{PIPE_BUF} bytes of buffering (@pxref{Ports and File
2232 Descriptors}), which will be enough for small writes, but not for say
2233 putting a big file through a filter.
2236 @deffn {Scheme Procedure} open-input-pipe command
2237 Equivalent to @code{open-pipe} with mode @code{OPEN_READ}.
2240 (let* ((port (open-input-pipe "date --utc"))
2241 (str (read-line port)))
2244 @result{} "Mon Mar 11 20:10:44 UTC 2002"
2248 @deffn {Scheme Procedure} open-output-pipe command
2249 Equivalent to @code{open-pipe} with mode @code{OPEN_WRITE}.
2252 (let ((port (open-output-pipe "lpr")))
2253 (display "Something for the line printer.\n" port)
2254 (if (not (eqv? 0 (status:exit-val (close-pipe port))))
2255 (error "Cannot print")))
2259 @deffn {Scheme Procedure} open-input-output-pipe command
2260 Equivalent to @code{open-pipe} with mode @code{OPEN_BOTH}.
2264 @deffn {Scheme Procedure} close-pipe port
2265 Close a pipe created by @code{open-pipe}, wait for the process to
2266 terminate, and return the wait status code. The status is as per
2267 @code{waitpid} and can be decoded with @code{status:exit-val} etc
2272 @code{waitpid WAIT_ANY} should not be used when pipes are open, since
2273 it can reap a pipe's child process, causing an error from a subsequent
2276 @code{close-port} (@pxref{Closing}) can close a pipe, but it doesn't
2277 reap the child process.
2279 The garbage collector will close a pipe no longer in use, and reap the
2280 child process with @code{waitpid}. If the child hasn't yet terminated
2281 the garbage collector doesn't block, but instead checks again in the
2284 Many systems have per-user and system-wide limits on the number of
2285 processes, and a system-wide limit on the number of pipes, so pipes
2286 should be closed explicitly when no longer needed, rather than letting
2287 the garbage collector pick them up at some later time.
2291 @subsection Networking
2295 * Network Address Conversion::
2296 * Network Databases::
2297 * Network Socket Address::
2298 * Network Sockets and Communication::
2299 * Internet Socket Examples::
2302 @node Network Address Conversion
2303 @subsubsection Network Address Conversion
2304 @cindex network address
2306 This section describes procedures which convert internet addresses
2307 between numeric and string formats.
2309 @subsubheading IPv4 Address Conversion
2312 An IPv4 Internet address is a 4-byte value, represented in Guile as an
2313 integer in host byte order, so that say ``0.0.0.1'' is 1, or
2314 ``1.0.0.0'' is 16777216.
2316 Some underlying C functions use network byte order for addresses,
2317 Guile converts as necessary so that at the Scheme level its host byte
2321 For a server, this can be used with @code{bind} (@pxref{Network
2322 Sockets and Communication}) to allow connections from any interface on
2326 @defvar INADDR_BROADCAST
2327 The broadcast address on the local network.
2330 @defvar INADDR_LOOPBACK
2331 The address of the local host using the loopback device, ie.@:
2335 @c INADDR_NONE is defined in the code, but serves no purpose.
2336 @c inet_addr() returns it as an error indication, but that function
2337 @c isn't provided, for the good reason that inet_aton() does the same
2338 @c job and gives an unambiguous error indication. (INADDR_NONE is a
2339 @c valid 4-byte value, in glibc it's the same as INADDR_BROADCAST.)
2341 @c @defvar INADDR_NONE
2345 @deffn {Scheme Procedure} inet-aton address
2346 @deffnx {C Function} scm_inet_aton (address)
2347 This function is deprecated in favor of @code{inet-pton}.
2349 Convert an IPv4 Internet address from printable string
2350 (dotted decimal notation) to an integer. E.g.,
2353 (inet-aton "127.0.0.1") @result{} 2130706433
2357 @deffn {Scheme Procedure} inet-ntoa inetid
2358 @deffnx {C Function} scm_inet_ntoa (inetid)
2359 This function is deprecated in favor of @code{inet-ntop}.
2361 Convert an IPv4 Internet address to a printable
2362 (dotted decimal notation) string. E.g.,
2365 (inet-ntoa 2130706433) @result{} "127.0.0.1"
2369 @deffn {Scheme Procedure} inet-netof address
2370 @deffnx {C Function} scm_inet_netof (address)
2371 Return the network number part of the given IPv4
2372 Internet address. E.g.,
2375 (inet-netof 2130706433) @result{} 127
2379 @deffn {Scheme Procedure} inet-lnaof address
2380 @deffnx {C Function} scm_lnaof (address)
2381 Return the local-address-with-network part of the given
2382 IPv4 Internet address, using the obsolete class A/B/C system.
2386 (inet-lnaof 2130706433) @result{} 1
2390 @deffn {Scheme Procedure} inet-makeaddr net lna
2391 @deffnx {C Function} scm_inet_makeaddr (net, lna)
2392 Make an IPv4 Internet address by combining the network number
2393 @var{net} with the local-address-within-network number
2397 (inet-makeaddr 127 1) @result{} 2130706433
2401 @subsubheading IPv6 Address Conversion
2404 An IPv6 Internet address is a 16-byte value, represented in Guile as
2405 an integer in host byte order, so that say ``::1'' is 1.
2407 @deffn {Scheme Procedure} inet-ntop family address
2408 @deffnx {C Function} scm_inet_ntop (family, address)
2409 Convert a network address from an integer to a printable string.
2410 @var{family} can be @code{AF_INET} or @code{AF_INET6}. E.g.,
2413 (inet-ntop AF_INET 2130706433) @result{} "127.0.0.1"
2414 (inet-ntop AF_INET6 (- (expt 2 128) 1))
2415 @result{} "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff"
2419 @deffn {Scheme Procedure} inet-pton family address
2420 @deffnx {C Function} scm_inet_pton (family, address)
2421 Convert a string containing a printable network address to an integer
2422 address. @var{family} can be @code{AF_INET} or @code{AF_INET6}.
2426 (inet-pton AF_INET "127.0.0.1") @result{} 2130706433
2427 (inet-pton AF_INET6 "::1") @result{} 1
2432 @node Network Databases
2433 @subsubsection Network Databases
2434 @cindex network database
2436 This section describes procedures which query various network databases.
2437 Care should be taken when using the database routines since they are not
2440 @subsubheading @code{getaddrinfo}
2442 @cindex @code{addrinfo} object type
2443 @cindex host name lookup
2444 @cindex service name lookup
2446 The @code{getaddrinfo} procedure maps host and service names to socket addresses
2447 and associated information in a protocol-independent way.
2449 @deffn {Scheme Procedure} getaddrinfo name service [hint_flags [hint_family [hint_socktype [hint_protocol]]]]
2450 @deffnx {C Function} scm_getaddrinfo (name, service, hint_flags, hint_family, hint_socktype, hint_protocol)
2451 Return a list of @code{addrinfo} structures containing
2452 a socket address and associated information for host @var{name}
2453 and/or @var{service} to be used in creating a socket with
2454 which to address the specified service.
2457 (let* ((ai (car (getaddrinfo "www.gnu.org" "http")))
2458 (s (socket (addrinfo:fam ai) (addrinfo:socktype ai)
2459 (addrinfo:protocol ai))))
2460 (connect s (addrinfo:addr ai))
2464 When @var{service} is omitted or is @code{#f}, return
2465 network-level addresses for @var{name}. When @var{name}
2466 is @code{#f} @var{service} must be provided and service
2467 locations local to the caller are returned.
2469 Additional hints can be provided. When specified,
2470 @var{hint_flags} should be a bitwise-or of zero or more
2471 constants among the following:
2475 Socket address is intended for @code{bind}.
2478 Request for canonical host name, available via
2479 @code{addrinfo:canonname}. This makes sense mainly when
2480 DNS lookups are involved.
2482 @item AI_NUMERICHOST
2483 Specifies that @var{name} is a numeric host address string
2484 (e.g., @code{"127.0.0.1"}), meaning that name resolution
2487 @item AI_NUMERICSERV
2488 Likewise, specifies that @var{service} is a numeric port
2489 string (e.g., @code{"80"}).
2492 Return only addresses configured on the local system It is
2493 highly recommended to provide this flag when the returned
2494 socket addresses are to be used to make connections;
2495 otherwise, some of the returned addresses could be unreachable
2496 or use a protocol that is not supported.
2499 When looking up IPv6 addresses, return mapped IPv4 addresses if
2500 there is no IPv6 address available at all.
2503 If this flag is set along with @code{AI_V4MAPPED} when looking up IPv6
2504 addresses, return all IPv6 addresses as well as all IPv4 addresses, the latter
2505 mapped to IPv6 format.
2508 When given, @var{hint_family} should specify the requested
2509 address family, e.g., @code{AF_INET6}. Similarly,
2510 @var{hint_socktype} should specify the requested socket type
2511 (e.g., @code{SOCK_DGRAM}), and @var{hint_protocol} should
2512 specify the requested protocol (its value is interpreted
2513 as in calls to @code{socket}).
2515 On error, an exception with key @code{getaddrinfo-error} is
2516 thrown, with an error code (an integer) as its argument:
2519 (catch 'getaddrinfo-error
2521 (getaddrinfo "www.gnu.org" "gopher"))
2522 (lambda (key errcode)
2523 (cond ((= errcode EAI_SERVICE)
2524 (display "doesn't know about Gopher!\n"))
2525 ((= errcode EAI_NONAME)
2526 (display "www.gnu.org not found\\n"))
2528 (format #t "something wrong: ~a\n"
2529 (gai-strerror errcode))))))
2536 The name or service could not be resolved at this time. Future
2537 attempts may succeed.
2540 @var{hint_flags} contains an invalid value.
2543 A non-recoverable error occurred when attempting to
2547 @var{hint_family} was not recognized.
2550 Either @var{name} does not resolve for the supplied parameters,
2551 or neither @var{name} nor @var{service} were supplied.
2554 This non-POSIX error code can be returned on some systems (GNU
2555 and Darwin, at least), for example when @var{name} is known
2556 but requests that were made turned out no data. Error handling
2557 code should be prepared to handle it when it is defined.
2560 @var{service} was not recognized for the specified socket type.
2563 @var{hint_socktype} was not recognized.
2566 A system error occurred. In C, the error code can be found in
2567 @code{errno}; this value is not accessible from Scheme, but in
2568 practice it provides little information about the actual error
2570 @c See <http://bugs.gnu.org/13958>.
2573 Users are encouraged to read the
2574 @url{http://www.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html,
2575 "POSIX specification} for more details.
2578 The following procedures take an @code{addrinfo} object as returned by
2581 @deffn {Scheme Procedure} addrinfo:flags ai
2582 Return flags for @var{ai} as a bitwise or of @code{AI_} values (see above).
2585 @deffn {Scheme Procedure} addrinfo:fam ai
2586 Return the address family of @var{ai} (a @code{AF_} value).
2589 @deffn {Scheme Procedure} addrinfo:socktype ai
2590 Return the socket type for @var{ai} (a @code{SOCK_} value).
2593 @deffn {Scheme Procedure} addrinfo:protocol ai
2594 Return the protocol of @var{ai}.
2597 @deffn {Scheme Procedure} addrinfo:addr ai
2598 Return the socket address associated with @var{ai} as a @code{sockaddr}
2599 object (@pxref{Network Socket Address}).
2602 @deffn {Scheme Procedure} addrinfo:canonname ai
2603 Return a string for the canonical name associated with @var{ai} if
2604 the @code{AI_CANONNAME} flag was supplied.
2607 @subsubheading The Host Database
2608 @cindex @file{/etc/hosts}
2609 @cindex network database
2611 A @dfn{host object} is a structure that represents what is known about a
2612 network host, and is the usual way of representing a system's network
2613 identity inside software.
2615 The following functions accept a host object and return a selected
2618 @deffn {Scheme Procedure} hostent:name host
2619 The ``official'' hostname for @var{host}.
2621 @deffn {Scheme Procedure} hostent:aliases host
2622 A list of aliases for @var{host}.
2624 @deffn {Scheme Procedure} hostent:addrtype host
2625 The host address type, one of the @code{AF} constants, such as
2626 @code{AF_INET} or @code{AF_INET6}.
2628 @deffn {Scheme Procedure} hostent:length host
2629 The length of each address for @var{host}, in bytes.
2631 @deffn {Scheme Procedure} hostent:addr-list host
2632 The list of network addresses associated with @var{host}. For
2633 @code{AF_INET} these are integer IPv4 address (@pxref{Network Address
2637 The following procedures can be used to search the host database. However,
2638 @code{getaddrinfo} should be preferred over them since it's more generic and
2641 @deffn {Scheme Procedure} gethost [host]
2642 @deffnx {Scheme Procedure} gethostbyname hostname
2643 @deffnx {Scheme Procedure} gethostbyaddr address
2644 @deffnx {C Function} scm_gethost (host)
2645 Look up a host by name or address, returning a host object. The
2646 @code{gethost} procedure will accept either a string name or an integer
2647 address; if given no arguments, it behaves like @code{gethostent} (see
2648 below). If a name or address is supplied but the address can not be
2649 found, an error will be thrown to one of the keys:
2650 @code{host-not-found}, @code{try-again}, @code{no-recovery} or
2651 @code{no-data}, corresponding to the equivalent @code{h_error} values.
2652 Unusual conditions may result in errors thrown to the
2653 @code{system-error} or @code{misc_error} keys.
2656 (gethost "www.gnu.org")
2657 @result{} #("www.gnu.org" () 2 4 (3353880842))
2659 (gethostbyname "www.emacs.org")
2660 @result{} #("emacs.org" ("www.emacs.org") 2 4 (1073448978))
2664 The following procedures may be used to step through the host
2665 database from beginning to end.
2667 @deffn {Scheme Procedure} sethostent [stayopen]
2668 Initialize an internal stream from which host objects may be read. This
2669 procedure must be called before any calls to @code{gethostent}, and may
2670 also be called afterward to reset the host entry stream. If
2671 @var{stayopen} is supplied and is not @code{#f}, the database is not
2672 closed by subsequent @code{gethostbyname} or @code{gethostbyaddr} calls,
2673 possibly giving an efficiency gain.
2676 @deffn {Scheme Procedure} gethostent
2677 Return the next host object from the host database, or @code{#f} if
2678 there are no more hosts to be found (or an error has been encountered).
2679 This procedure may not be used before @code{sethostent} has been called.
2682 @deffn {Scheme Procedure} endhostent
2683 Close the stream used by @code{gethostent}. The return value is unspecified.
2686 @deffn {Scheme Procedure} sethost [stayopen]
2687 @deffnx {C Function} scm_sethost (stayopen)
2688 If @var{stayopen} is omitted, this is equivalent to @code{endhostent}.
2689 Otherwise it is equivalent to @code{sethostent stayopen}.
2692 @subsubheading The Network Database
2693 @cindex network database
2695 The following functions accept an object representing a network
2696 and return a selected component:
2698 @deffn {Scheme Procedure} netent:name net
2699 The ``official'' network name.
2701 @deffn {Scheme Procedure} netent:aliases net
2702 A list of aliases for the network.
2704 @deffn {Scheme Procedure} netent:addrtype net
2705 The type of the network number. Currently, this returns only
2708 @deffn {Scheme Procedure} netent:net net
2712 The following procedures are used to search the network database:
2714 @deffn {Scheme Procedure} getnet [net]
2715 @deffnx {Scheme Procedure} getnetbyname net-name
2716 @deffnx {Scheme Procedure} getnetbyaddr net-number
2717 @deffnx {C Function} scm_getnet (net)
2718 Look up a network by name or net number in the network database. The
2719 @var{net-name} argument must be a string, and the @var{net-number}
2720 argument must be an integer. @code{getnet} will accept either type of
2721 argument, behaving like @code{getnetent} (see below) if no arguments are
2725 The following procedures may be used to step through the network
2726 database from beginning to end.
2728 @deffn {Scheme Procedure} setnetent [stayopen]
2729 Initialize an internal stream from which network objects may be read. This
2730 procedure must be called before any calls to @code{getnetent}, and may
2731 also be called afterward to reset the net entry stream. If
2732 @var{stayopen} is supplied and is not @code{#f}, the database is not
2733 closed by subsequent @code{getnetbyname} or @code{getnetbyaddr} calls,
2734 possibly giving an efficiency gain.
2737 @deffn {Scheme Procedure} getnetent
2738 Return the next entry from the network database.
2741 @deffn {Scheme Procedure} endnetent
2742 Close the stream used by @code{getnetent}. The return value is unspecified.
2745 @deffn {Scheme Procedure} setnet [stayopen]
2746 @deffnx {C Function} scm_setnet (stayopen)
2747 If @var{stayopen} is omitted, this is equivalent to @code{endnetent}.
2748 Otherwise it is equivalent to @code{setnetent stayopen}.
2751 @subsubheading The Protocol Database
2752 @cindex @file{/etc/protocols}
2754 @cindex network protocols
2756 The following functions accept an object representing a protocol
2757 and return a selected component:
2759 @deffn {Scheme Procedure} protoent:name protocol
2760 The ``official'' protocol name.
2762 @deffn {Scheme Procedure} protoent:aliases protocol
2763 A list of aliases for the protocol.
2765 @deffn {Scheme Procedure} protoent:proto protocol
2766 The protocol number.
2769 The following procedures are used to search the protocol database:
2771 @deffn {Scheme Procedure} getproto [protocol]
2772 @deffnx {Scheme Procedure} getprotobyname name
2773 @deffnx {Scheme Procedure} getprotobynumber number
2774 @deffnx {C Function} scm_getproto (protocol)
2775 Look up a network protocol by name or by number. @code{getprotobyname}
2776 takes a string argument, and @code{getprotobynumber} takes an integer
2777 argument. @code{getproto} will accept either type, behaving like
2778 @code{getprotoent} (see below) if no arguments are supplied.
2781 The following procedures may be used to step through the protocol
2782 database from beginning to end.
2784 @deffn {Scheme Procedure} setprotoent [stayopen]
2785 Initialize an internal stream from which protocol objects may be read. This
2786 procedure must be called before any calls to @code{getprotoent}, and may
2787 also be called afterward to reset the protocol entry stream. If
2788 @var{stayopen} is supplied and is not @code{#f}, the database is not
2789 closed by subsequent @code{getprotobyname} or @code{getprotobynumber} calls,
2790 possibly giving an efficiency gain.
2793 @deffn {Scheme Procedure} getprotoent
2794 Return the next entry from the protocol database.
2797 @deffn {Scheme Procedure} endprotoent
2798 Close the stream used by @code{getprotoent}. The return value is unspecified.
2801 @deffn {Scheme Procedure} setproto [stayopen]
2802 @deffnx {C Function} scm_setproto (stayopen)
2803 If @var{stayopen} is omitted, this is equivalent to @code{endprotoent}.
2804 Otherwise it is equivalent to @code{setprotoent stayopen}.
2807 @subsubheading The Service Database
2808 @cindex @file{/etc/services}
2810 @cindex network services
2812 The following functions accept an object representing a service
2813 and return a selected component:
2815 @deffn {Scheme Procedure} servent:name serv
2816 The ``official'' name of the network service.
2818 @deffn {Scheme Procedure} servent:aliases serv
2819 A list of aliases for the network service.
2821 @deffn {Scheme Procedure} servent:port serv
2822 The Internet port used by the service.
2824 @deffn {Scheme Procedure} servent:proto serv
2825 The protocol used by the service. A service may be listed many times
2826 in the database under different protocol names.
2829 The following procedures are used to search the service database:
2831 @deffn {Scheme Procedure} getserv [name [protocol]]
2832 @deffnx {Scheme Procedure} getservbyname name protocol
2833 @deffnx {Scheme Procedure} getservbyport port protocol
2834 @deffnx {C Function} scm_getserv (name, protocol)
2835 Look up a network service by name or by service number, and return a
2836 network service object. The @var{protocol} argument specifies the name
2837 of the desired protocol; if the protocol found in the network service
2838 database does not match this name, a system error is signalled.
2840 The @code{getserv} procedure will take either a service name or number
2841 as its first argument; if given no arguments, it behaves like
2842 @code{getservent} (see below).
2845 (getserv "imap" "tcp")
2846 @result{} #("imap2" ("imap") 143 "tcp")
2848 (getservbyport 88 "udp")
2849 @result{} #("kerberos" ("kerberos5" "krb5") 88 "udp")
2853 The following procedures may be used to step through the service
2854 database from beginning to end.
2856 @deffn {Scheme Procedure} setservent [stayopen]
2857 Initialize an internal stream from which service objects may be read. This
2858 procedure must be called before any calls to @code{getservent}, and may
2859 also be called afterward to reset the service entry stream. If
2860 @var{stayopen} is supplied and is not @code{#f}, the database is not
2861 closed by subsequent @code{getservbyname} or @code{getservbyport} calls,
2862 possibly giving an efficiency gain.
2865 @deffn {Scheme Procedure} getservent
2866 Return the next entry from the services database.
2869 @deffn {Scheme Procedure} endservent
2870 Close the stream used by @code{getservent}. The return value is unspecified.
2873 @deffn {Scheme Procedure} setserv [stayopen]
2874 @deffnx {C Function} scm_setserv (stayopen)
2875 If @var{stayopen} is omitted, this is equivalent to @code{endservent}.
2876 Otherwise it is equivalent to @code{setservent stayopen}.
2880 @node Network Socket Address
2881 @subsubsection Network Socket Address
2882 @cindex socket address
2883 @cindex network socket address
2884 @tpindex Socket address
2886 A @dfn{socket address} object identifies a socket endpoint for
2887 communication. In the case of @code{AF_INET} for instance, the socket
2888 address object comprises the host address (or interface on the host)
2889 and a port number which specifies a particular open socket in a
2890 running client or server process. A socket address object can be
2893 @deffn {Scheme Procedure} make-socket-address AF_INET ipv4addr port
2894 @deffnx {Scheme Procedure} make-socket-address AF_INET6 ipv6addr port [flowinfo [scopeid]]
2895 @deffnx {Scheme Procedure} make-socket-address AF_UNIX path
2896 @deffnx {C Function} scm_make_socket_address (family, address, arglist)
2897 Return a new socket address object. The first argument is the address
2898 family, one of the @code{AF} constants, then the arguments vary
2899 according to the family.
2901 For @code{AF_INET} the arguments are an IPv4 network address number
2902 (@pxref{Network Address Conversion}), and a port number.
2904 For @code{AF_INET6} the arguments are an IPv6 network address number
2905 and a port number. Optional @var{flowinfo} and @var{scopeid}
2906 arguments may be given (both integers, default 0).
2908 For @code{AF_UNIX} the argument is a filename (a string).
2910 The C function @code{scm_make_socket_address} takes the @var{family}
2911 and @var{address} arguments directly, then @var{arglist} is a list of
2912 further arguments, being the port for IPv4, port and optional flowinfo
2913 and scopeid for IPv6, or the empty list @code{SCM_EOL} for Unix
2918 The following functions access the fields of a socket address object,
2920 @deffn {Scheme Procedure} sockaddr:fam sa
2921 Return the address family from socket address object @var{sa}. This
2922 is one of the @code{AF} constants (e.g.@: @code{AF_INET}).
2925 @deffn {Scheme Procedure} sockaddr:path sa
2926 For an @code{AF_UNIX} socket address object @var{sa}, return the
2930 @deffn {Scheme Procedure} sockaddr:addr sa
2931 For an @code{AF_INET} or @code{AF_INET6} socket address object
2932 @var{sa}, return the network address number.
2935 @deffn {Scheme Procedure} sockaddr:port sa
2936 For an @code{AF_INET} or @code{AF_INET6} socket address object
2937 @var{sa}, return the port number.
2940 @deffn {Scheme Procedure} sockaddr:flowinfo sa
2941 For an @code{AF_INET6} socket address object @var{sa}, return the
2945 @deffn {Scheme Procedure} sockaddr:scopeid sa
2946 For an @code{AF_INET6} socket address object @var{sa}, return the
2950 @tpindex @code{struct sockaddr}
2951 @tpindex @code{sockaddr}
2952 The functions below convert to and from the C @code{struct sockaddr}
2953 (@pxref{Address Formats,,, libc, The GNU C Library Reference Manual}).
2954 That structure is a generic type, an application can cast to or from
2955 @code{struct sockaddr_in}, @code{struct sockaddr_in6} or @code{struct
2956 sockaddr_un} according to the address family.
2958 In a @code{struct sockaddr} taken or returned, the byte ordering in
2959 the fields follows the C conventions (@pxref{Byte Order,, Byte Order
2960 Conversion, libc, The GNU C Library Reference Manual}). This means
2961 network byte order for @code{AF_INET} host address
2962 (@code{sin_addr.s_addr}) and port number (@code{sin_port}), and
2963 @code{AF_INET6} port number (@code{sin6_port}). But at the Scheme
2964 level these values are taken or returned in host byte order, so the
2965 port is an ordinary integer, and the host address likewise is an
2966 ordinary integer (as described in @ref{Network Address Conversion}).
2968 @deftypefn {C Function} {struct sockaddr *} scm_c_make_socket_address (SCM family, SCM address, SCM args, size_t *outsize)
2969 Return a newly-@code{malloc}ed @code{struct sockaddr} created from
2970 arguments like those taken by @code{scm_make_socket_address} above.
2972 The size (in bytes) of the @code{struct sockaddr} return is stored
2973 into @code{*@var{outsize}}. An application must call @code{free} to
2974 release the returned structure when no longer required.
2977 @deftypefn {C Function} SCM scm_from_sockaddr (const struct sockaddr *address, unsigned address_size)
2978 Return a Scheme socket address object from the C @var{address}
2979 structure. @var{address_size} is the size in bytes of @var{address}.
2982 @deftypefn {C Function} {struct sockaddr *} scm_to_sockaddr (SCM address, size_t *address_size)
2983 Return a newly-@code{malloc}ed @code{struct sockaddr} from a Scheme
2984 level socket address object.
2986 The size (in bytes) of the @code{struct sockaddr} return is stored
2987 into @code{*@var{outsize}}. An application must call @code{free} to
2988 release the returned structure when no longer required.
2992 @node Network Sockets and Communication
2993 @subsubsection Network Sockets and Communication
2995 @cindex network socket
2997 Socket ports can be created using @code{socket} and @code{socketpair}.
2998 The ports are initially unbuffered, to make reading and writing to the
2999 same port more reliable. A buffer can be added to the port using
3000 @code{setvbuf}; see @ref{Ports and File Descriptors}.
3002 Most systems have limits on how many files and sockets can be open, so
3003 it's strongly recommended that socket ports be closed explicitly when
3004 no longer required (@pxref{Ports}).
3006 Some of the underlying C functions take values in network byte order,
3007 but the convention in Guile is that at the Scheme level everything is
3008 ordinary host byte order and conversions are made automatically where
3011 @deffn {Scheme Procedure} socket family style proto
3012 @deffnx {C Function} scm_socket (family, style, proto)
3013 Return a new socket port of the type specified by @var{family},
3014 @var{style} and @var{proto}. All three parameters are integers. The
3015 possible values for @var{family} are as follows, where supported by
3023 The possible values for @var{style} are as follows, again where
3024 supported by the system,
3030 @defvarx SOCK_SEQPACKET
3033 @var{proto} can be obtained from a protocol name using
3034 @code{getprotobyname} (@pxref{Network Databases}). A value of zero
3035 means the default protocol, which is usually right.
3037 A socket cannot by used for communication until it has been connected
3038 somewhere, usually with either @code{connect} or @code{accept} below.
3041 @deffn {Scheme Procedure} socketpair family style proto
3042 @deffnx {C Function} scm_socketpair (family, style, proto)
3043 Return a pair, the @code{car} and @code{cdr} of which are two unnamed
3044 socket ports connected to each other. The connection is full-duplex,
3045 so data can be transferred in either direction between the two.
3047 @var{family}, @var{style} and @var{proto} are as per @code{socket}
3048 above. But many systems only support socket pairs in the
3049 @code{PF_UNIX} family. Zero is likely to be the only meaningful value
3053 @deffn {Scheme Procedure} getsockopt sock level optname
3054 @deffnx {Scheme Procedure} setsockopt sock level optname value
3055 @deffnx {C Function} scm_getsockopt (sock, level, optname)
3056 @deffnx {C Function} scm_setsockopt (sock, level, optname, value)
3057 Get or set an option on socket port @var{sock}. @code{getsockopt}
3058 returns the current value. @code{setsockopt} sets a value and the
3059 return is unspecified.
3061 @var{level} is an integer specifying a protocol layer, either
3062 @code{SOL_SOCKET} for socket level options, or a protocol number from
3063 the @code{IPPROTO} constants or @code{getprotoent} (@pxref{Network
3068 @defvarx IPPROTO_TCP
3069 @defvarx IPPROTO_UDP
3072 @var{optname} is an integer specifying an option within the protocol
3075 For @code{SOL_SOCKET} level the following @var{optname}s are defined
3076 (when provided by the system). For their meaning see
3077 @ref{Socket-Level Options,,, libc, The GNU C Library Reference
3078 Manual}, or @command{man 7 socket}.
3081 @defvarx SO_REUSEADDR
3085 @defvarx SO_DONTROUTE
3086 @defvarx SO_BROADCAST
3089 @defvarx SO_KEEPALIVE
3090 @defvarx SO_OOBINLINE
3091 @defvarx SO_NO_CHECK
3092 @defvarx SO_PRIORITY
3093 @defvarx SO_REUSEPORT
3094 The @var{value} taken or returned is an integer.
3098 The @var{value} taken or returned is a pair of integers
3099 @code{(@var{ENABLE} . @var{TIMEOUT})}. On old systems without timeout
3100 support (ie.@: without @code{struct linger}), only @var{ENABLE} has an
3101 effect but the value in Guile is always a pair.
3104 @c Note that we refer only to ``man ip'' here. On GNU/Linux it's
3105 @c ``man 7 ip'' but on NetBSD it's ``man 4 ip''.
3107 For IP level (@code{IPPROTO_IP}) the following @var{optname}s are
3108 defined (when provided by the system). See @command{man ip} for what
3111 @defvar IP_MULTICAST_IF
3112 This sets the source interface used by multicast traffic.
3115 @defvar IP_MULTICAST_TTL
3116 This sets the default TTL for multicast traffic. This defaults
3117 to 1 and should be increased to allow traffic to pass beyond the
3121 @defvar IP_ADD_MEMBERSHIP
3122 @defvarx IP_DROP_MEMBERSHIP
3123 These can be used only with @code{setsockopt}, not @code{getsockopt}.
3124 @var{value} is a pair @code{(@var{MULTIADDR} . @var{INTERFACEADDR})}
3125 of integer IPv4 addresses (@pxref{Network Address Conversion}).
3126 @var{MULTIADDR} is a multicast address to be added to or dropped from
3127 the interface @var{INTERFACEADDR}. @var{INTERFACEADDR} can be
3128 @code{INADDR_ANY} to have the system select the interface.
3129 @var{INTERFACEADDR} can also be an interface index number, on systems
3134 @deffn {Scheme Procedure} shutdown sock how
3135 @deffnx {C Function} scm_shutdown (sock, how)
3136 Sockets can be closed simply by using @code{close-port}. The
3137 @code{shutdown} procedure allows reception or transmission on a
3138 connection to be shut down individually, according to the parameter
3143 Stop receiving data for this socket. If further data arrives, reject it.
3145 Stop trying to transmit data from this socket. Discard any
3146 data waiting to be sent. Stop looking for acknowledgement of
3147 data already sent; don't retransmit it if it is lost.
3149 Stop both reception and transmission.
3152 The return value is unspecified.
3155 @deffn {Scheme Procedure} connect sock sockaddr
3156 @deffnx {Scheme Procedure} connect sock AF_INET ipv4addr port
3157 @deffnx {Scheme Procedure} connect sock AF_INET6 ipv6addr port [flowinfo [scopeid]]
3158 @deffnx {Scheme Procedure} connect sock AF_UNIX path
3159 @deffnx {C Function} scm_connect (sock, fam, address, args)
3160 Initiate a connection on socket port @var{sock} to a given address.
3161 The destination is either a socket address object, or arguments the
3162 same as @code{make-socket-address} would take to make such an object
3163 (@pxref{Network Socket Address}). The return value is unspecified.
3166 (connect sock AF_INET INADDR_LOOPBACK 23)
3167 (connect sock (make-socket-address AF_INET INADDR_LOOPBACK 23))
3171 @deffn {Scheme Procedure} bind sock sockaddr
3172 @deffnx {Scheme Procedure} bind sock AF_INET ipv4addr port
3173 @deffnx {Scheme Procedure} bind sock AF_INET6 ipv6addr port [flowinfo [scopeid]]
3174 @deffnx {Scheme Procedure} bind sock AF_UNIX path
3175 @deffnx {C Function} scm_bind (sock, fam, address, args)
3176 Bind socket port @var{sock} to the given address. The address is
3177 either a socket address object, or arguments the same as
3178 @code{make-socket-address} would take to make such an object
3179 (@pxref{Network Socket Address}). The return value is unspecified.
3181 Generally a socket is only explicitly bound to a particular address
3182 when making a server, i.e.@: to listen on a particular port. For an
3183 outgoing connection the system will assign a local address
3184 automatically, if not already bound.
3187 (bind sock AF_INET INADDR_ANY 12345)
3188 (bind sock (make-socket-address AF_INET INADDR_ANY 12345))
3192 @deffn {Scheme Procedure} listen sock backlog
3193 @deffnx {C Function} scm_listen (sock, backlog)
3194 Enable @var{sock} to accept connection
3195 requests. @var{backlog} is an integer specifying
3196 the maximum length of the queue for pending connections.
3197 If the queue fills, new clients will fail to connect until
3198 the server calls @code{accept} to accept a connection from
3201 The return value is unspecified.
3204 @deffn {Scheme Procedure} accept sock
3205 @deffnx {C Function} scm_accept (sock)
3206 Accept a connection from socket port @var{sock} which has been enabled
3207 for listening with @code{listen} above. If there are no incoming
3208 connections in the queue, wait until one is available (unless
3209 @code{O_NONBLOCK} has been set on the socket, @pxref{Ports and File
3210 Descriptors,@code{fcntl}}).
3212 The return value is a pair. The @code{car} is a new socket port,
3213 connected and ready to communicate. The @code{cdr} is a socket
3214 address object (@pxref{Network Socket Address}) which is where the
3215 remote connection is from (like @code{getpeername} below).
3217 All communication takes place using the new socket returned. The
3218 given @var{sock} remains bound and listening, and @code{accept} may be
3219 called on it again to get another incoming connection when desired.
3222 @deffn {Scheme Procedure} getsockname sock
3223 @deffnx {C Function} scm_getsockname (sock)
3224 Return a socket address object which is the where @var{sock} is bound
3225 locally. @var{sock} may have obtained its local address from
3226 @code{bind} (above), or if a @code{connect} is done with an otherwise
3227 unbound socket (which is usual) then the system will have assigned an
3230 Note that on many systems the address of a socket in the
3231 @code{AF_UNIX} namespace cannot be read.
3234 @deffn {Scheme Procedure} getpeername sock
3235 @deffnx {C Function} scm_getpeername (sock)
3236 Return a socket address object which is where @var{sock} is connected
3237 to, i.e.@: the remote endpoint.
3239 Note that on many systems the address of a socket in the
3240 @code{AF_UNIX} namespace cannot be read.
3243 @deffn {Scheme Procedure} recv! sock buf [flags]
3244 @deffnx {C Function} scm_recv (sock, buf, flags)
3245 Receive data from a socket port.
3246 @var{sock} must already
3247 be bound to the address from which data is to be received.
3248 @var{buf} is a bytevector into which
3249 the data will be written. The size of @var{buf} limits
3251 data which can be received: in the case of packet
3252 protocols, if a packet larger than this limit is encountered
3254 will be irrevocably lost.
3258 @vindex MSG_DONTROUTE
3259 The optional @var{flags} argument is a value or bitwise OR of
3260 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3262 The value returned is the number of bytes read from the
3265 Note that the data is read directly from the socket file
3267 any unread buffered port data is ignored.
3270 @deffn {Scheme Procedure} send sock message [flags]
3271 @deffnx {C Function} scm_send (sock, message, flags)
3274 @vindex MSG_DONTROUTE
3275 Transmit bytevector @var{message} on socket port @var{sock}.
3276 @var{sock} must already be bound to a destination address. The value
3277 returned is the number of bytes transmitted---it's possible for this
3278 to be less than the length of @var{message} if the socket is set to be
3279 non-blocking. The optional @var{flags} argument is a value or bitwise
3280 OR of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3282 Note that the data is written directly to the socket
3284 any unflushed buffered port data is ignored.
3287 @deffn {Scheme Procedure} recvfrom! sock buf [flags [start [end]]]
3288 @deffnx {C Function} scm_recvfrom (sock, buf, flags, start, end)
3289 Receive data from socket port @var{sock}, returning the originating
3290 address as well as the data. This function is usually for datagram
3291 sockets, but can be used on stream-oriented sockets too.
3293 The data received is stored in bytevector @var{buf}, using
3294 either the whole bytevector or just the region between the optional
3295 @var{start} and @var{end} positions. The size of @var{buf}
3296 limits the amount of data that can be received. For datagram
3297 protocols if a packet larger than this is received then excess
3298 bytes are irrevocably lost.
3300 The return value is a pair. The @code{car} is the number of bytes
3301 read. The @code{cdr} is a socket address object (@pxref{Network
3302 Socket Address}) which is where the data came from, or @code{#f} if
3303 the origin is unknown.
3307 @vindex MSG_DONTROUTE
3308 The optional @var{flags} argument is a or bitwise-OR (@code{logior})
3309 of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3311 Data is read directly from the socket file descriptor, any buffered
3312 port data is ignored.
3314 @c This was linux kernel 2.6.15 and glibc 2.3.6, not sure what any
3315 @c specs are supposed to say about recvfrom threading.
3317 On a GNU/Linux system @code{recvfrom!} is not multi-threading, all
3318 threads stop while a @code{recvfrom!} call is in progress. An
3319 application may need to use @code{select}, @code{O_NONBLOCK} or
3320 @code{MSG_DONTWAIT} to avoid this.
3323 @deffn {Scheme Procedure} sendto sock message sockaddr [flags]
3324 @deffnx {Scheme Procedure} sendto sock message AF_INET ipv4addr port [flags]
3325 @deffnx {Scheme Procedure} sendto sock message AF_INET6 ipv6addr port [flowinfo [scopeid [flags]]]
3326 @deffnx {Scheme Procedure} sendto sock message AF_UNIX path [flags]
3327 @deffnx {C Function} scm_sendto (sock, message, fam, address, args_and_flags)
3328 Transmit bytevector @var{message} as a datagram socket port
3329 @var{sock}. The destination is specified either as a socket address
3330 object, or as arguments the same as would be taken by
3331 @code{make-socket-address} to create such an object (@pxref{Network
3334 The destination address may be followed by an optional @var{flags}
3335 argument which is a @code{logior} (@pxref{Bitwise Operations}) of
3336 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3338 The value returned is the number of bytes transmitted --
3340 this to be less than the length of @var{message} if the
3342 set to be non-blocking.
3343 Note that the data is written directly to the socket
3345 any unflushed buffered port data is ignored.
3348 The following functions can be used to convert short and long integers
3349 between ``host'' and ``network'' order. Although the procedures above do
3350 this automatically for addresses, the conversion will still need to
3351 be done when sending or receiving encoded integer data from the network.
3353 @deffn {Scheme Procedure} htons value
3354 @deffnx {C Function} scm_htons (value)
3355 Convert a 16 bit quantity from host to network byte ordering.
3356 @var{value} is packed into 2 bytes, which are then converted
3357 and returned as a new integer.
3360 @deffn {Scheme Procedure} ntohs value
3361 @deffnx {C Function} scm_ntohs (value)
3362 Convert a 16 bit quantity from network to host byte ordering.
3363 @var{value} is packed into 2 bytes, which are then converted
3364 and returned as a new integer.
3367 @deffn {Scheme Procedure} htonl value
3368 @deffnx {C Function} scm_htonl (value)
3369 Convert a 32 bit quantity from host to network byte ordering.
3370 @var{value} is packed into 4 bytes, which are then converted
3371 and returned as a new integer.
3374 @deffn {Scheme Procedure} ntohl value
3375 @deffnx {C Function} scm_ntohl (value)
3376 Convert a 32 bit quantity from network to host byte ordering.
3377 @var{value} is packed into 4 bytes, which are then converted
3378 and returned as a new integer.
3381 These procedures are inconvenient to use at present, but consider:
3384 (define write-network-long
3385 (lambda (value port)
3386 (let ((v (make-uniform-vector 1 1 0)))
3387 (uniform-vector-set! v 0 (htonl value))
3388 (uniform-vector-write v port))))
3390 (define read-network-long
3392 (let ((v (make-uniform-vector 1 1 0)))
3393 (uniform-vector-read! v port)
3394 (ntohl (uniform-vector-ref v 0)))))
3398 @node Internet Socket Examples
3399 @subsubsection Network Socket Examples
3400 @cindex network examples
3401 @cindex socket examples
3403 The following give examples of how to use network sockets.
3405 @subsubheading Internet Socket Client Example
3407 @cindex socket client example
3408 The following example demonstrates an Internet socket client.
3409 It connects to the HTTP daemon running on the local machine and
3410 returns the contents of the root index URL.
3413 (let ((s (socket PF_INET SOCK_STREAM 0)))
3414 (connect s AF_INET (inet-pton AF_INET "127.0.0.1") 80)
3415 (display "GET / HTTP/1.0\r\n\r\n" s)
3417 (do ((line (read-line s) (read-line s)))
3418 ((eof-object? line))
3424 @subsubheading Internet Socket Server Example
3426 @cindex socket server example
3427 The following example shows a simple Internet server which listens on
3428 port 2904 for incoming connections and sends a greeting back to the
3432 (let ((s (socket PF_INET SOCK_STREAM 0)))
3433 (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
3434 ;; @r{Specific address?}
3435 ;; @r{(bind s AF_INET (inet-pton AF_INET "127.0.0.1") 2904)}
3436 (bind s AF_INET INADDR_ANY 2904)
3439 (simple-format #t "Listening for clients in pid: ~S" (getpid))
3443 (let* ((client-connection (accept s))
3444 (client-details (cdr client-connection))
3445 (client (car client-connection)))
3446 (simple-format #t "Got new client connection: ~S"
3449 (simple-format #t "Client address: ~S"
3451 (sockaddr:addr client-details)))
3453 ;; @r{Send back the greeting to the client port}
3454 (display "Hello client\r\n" client)
3459 @node System Identification
3460 @subsection System Identification
3463 This section lists the various procedures Guile provides for accessing
3464 information about the system it runs on.
3466 @deffn {Scheme Procedure} uname
3467 @deffnx {C Function} scm_uname ()
3468 Return an object with some information about the computer
3469 system the program is running on.
3471 The following procedures accept an object as returned by @code{uname}
3472 and return a selected component (all of which are strings).
3474 @deffn {Scheme Procedure} utsname:sysname un
3475 The name of the operating system.
3477 @deffn {Scheme Procedure} utsname:nodename un
3478 The network name of the computer.
3480 @deffn {Scheme Procedure} utsname:release un
3481 The current release level of the operating system implementation.
3483 @deffn {Scheme Procedure} utsname:version un
3484 The current version level within the release of the operating system.
3486 @deffn {Scheme Procedure} utsname:machine un
3487 A description of the hardware.
3491 @deffn {Scheme Procedure} gethostname
3492 @deffnx {C Function} scm_gethostname ()
3494 Return the host name of the current processor.
3497 @deffn {Scheme Procedure} sethostname name
3498 @deffnx {C Function} scm_sethostname (name)
3499 Set the host name of the current processor to @var{name}. May
3500 only be used by the superuser. The return value is not
3508 @deffn {Scheme Procedure} setlocale category [locale]
3509 @deffnx {C Function} scm_setlocale (category, locale)
3510 Get or set the current locale, used for various internationalizations.
3511 Locales are strings, such as @samp{sv_SE}.
3513 If @var{locale} is given then the locale for the given @var{category}
3514 is set and the new value returned. If @var{locale} is not given then
3515 the current value is returned. @var{category} should be one of the
3516 following values (@pxref{Locale Categories, Categories of Activities
3517 that Locales Affect,, libc, The GNU C Library Reference Manual}):
3522 @defvarx LC_MESSAGES
3523 @defvarx LC_MONETARY
3529 A common usage is @samp{(setlocale LC_ALL "")}, which initializes all
3530 categories based on standard environment variables (@code{LANG} etc).
3531 For full details on categories and locale names @pxref{Locales,,
3532 Locales and Internationalization, libc, The GNU C Library Reference
3535 Note that @code{setlocale} affects locale settings for the whole
3536 process. @xref{i18n Introduction, locale objects and
3537 @code{make-locale}}, for a thread-safe alternative.
3541 @subsection Encryption
3544 Please note that the procedures in this section are not suited for
3545 strong encryption, they are only interfaces to the well-known and
3546 common system library functions of the same name. They are just as good
3547 (or bad) as the underlying functions, so you should refer to your system
3548 documentation before using them (@pxref{crypt,, Encrypting Passwords,
3549 libc, The GNU C Library Reference Manual}).
3551 @deffn {Scheme Procedure} crypt key salt
3552 @deffnx {C Function} scm_crypt (key, salt)
3553 Encrypt @var{key}, with the addition of @var{salt} (both strings),
3554 using the @code{crypt} C library call.
3557 Although @code{getpass} is not an encryption procedure per se, it
3558 appears here because it is often used in combination with @code{crypt}:
3560 @deffn {Scheme Procedure} getpass prompt
3561 @deffnx {C Function} scm_getpass (prompt)
3563 Display @var{prompt} to the standard error output and read
3564 a password from @file{/dev/tty}. If this file is not
3565 accessible, it reads from standard input. The password may be
3566 up to 127 characters in length. Additional characters and the
3567 terminating newline character are discarded. While reading
3568 the password, echoing and the generation of signals by special
3569 characters is disabled.
3574 @c TeX-master: "guile.texi"