2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004
4 @c 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 fd
215 @deffnx {C Function} scm_fdes_to_ports (fd)
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 fd
234 @deffnx {C Function} scm_primitive_move_to_fdes (port, fd)
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 object
256 @deffnx {C Function} scm_fsync (object)
257 Copies any unwritten data for the specified output file descriptor to disk.
258 If @var{port/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 new
406 @deffnx {C Function} scm_redirect_port (old, new)
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 object cmd [value]
476 @deffnx {C Function} scm_fcntl (object, cmd, value)
477 Apply @var{command} to the specified file descriptor or the underlying
478 file descriptor of the specified port. @var{value} is an optional
481 Values for @var{command} are:
484 Duplicate a file descriptor
487 Get flags associated with the file descriptor.
490 Set flags associated with the file descriptor to @var{value}.
493 Get flags associated with the open file.
496 Set flags associated with the open file to @var{value}
499 Get the process ID of a socket's owner, for @code{SIGIO} signals.
502 Set the process that owns a socket to @var{value}, for @code{SIGIO} signals.
505 The value used to indicate the ``close on exec'' flag with @code{F_GETFL} or
510 @deffn {Scheme Procedure} flock file operation
511 @deffnx {C Function} scm_flock (file, operation)
513 Apply or remove an advisory lock on an open file.
514 @var{operation} specifies the action to be done:
517 Shared lock. More than one process may hold a shared lock
518 for a given file at a given time.
521 Exclusive lock. Only one process may hold an exclusive lock
522 for a given file at a given time.
528 Don't block when locking. This is combined with one of the other
529 operations using @code{logior} (@pxref{Bitwise Operations}). If
530 @code{flock} would block an @code{EWOULDBLOCK} error is thrown
531 (@pxref{Conventions}).
534 The return value is not specified. @var{file} may be an open
535 file descriptor or an open file descriptor port.
537 Note that @code{flock} does not lock files across NFS.
540 @deffn {Scheme Procedure} select reads writes excepts [secs [usecs]]
541 @deffnx {C Function} scm_select (reads, writes, excepts, secs, usecs)
542 This procedure has a variety of uses: waiting for the ability
543 to provide input, accept output, or the existence of
544 exceptional conditions on a collection of ports or file
545 descriptors, or waiting for a timeout to occur.
546 It also returns if interrupted by a signal.
548 @var{reads}, @var{writes} and @var{excepts} can be lists or
549 vectors, with each member a port or a file descriptor.
550 The value returned is a list of three corresponding
551 lists or vectors containing only the members which meet the
552 specified requirement. The ability of port buffers to
553 provide input or accept output is taken into account.
554 Ordering of the input lists or vectors is not preserved.
556 The optional arguments @var{secs} and @var{usecs} specify the
557 timeout. Either @var{secs} can be specified alone, as
558 either an integer or a real number, or both @var{secs} and
559 @var{usecs} can be specified as integers, in which case
560 @var{usecs} is an additional timeout expressed in
561 microseconds. If @var{secs} is omitted or is @code{#f} then
562 select will wait for as long as it takes for one of the other
563 conditions to be satisfied.
565 The scsh version of @code{select} differs as follows:
566 Only vectors are accepted for the first three arguments.
567 The @var{usecs} argument is not supported.
568 Multiple values are returned instead of a list.
569 Duplicates in the input vectors appear only once in output.
570 An additional @code{select!} interface is provided.
574 @subsection File System
577 These procedures allow querying and setting file system attributes
579 permissions, sizes and types of files); deleting, copying, renaming and
580 linking files; creating and removing directories and querying their
581 contents; syncing the file system and creating special files.
583 @deffn {Scheme Procedure} access? path how
584 @deffnx {C Function} scm_access (path, how)
585 Test accessibility of a file under the real UID and GID of the calling
586 process. The return is @code{#t} if @var{path} exists and the
587 permissions requested by @var{how} are all allowed, or @code{#f} if
590 @var{how} is an integer which is one of the following values, or a
591 bitwise-OR (@code{logior}) of multiple values.
594 Test for read permission.
597 Test for write permission.
600 Test for execute permission.
603 Test for existence of the file. This is implied by each of the other
604 tests, so there's no need to combine it with them.
607 It's important to note that @code{access?} does not simply indicate
608 what will happen on attempting to read or write a file. In normal
609 circumstances it does, but in a set-UID or set-GID program it doesn't
610 because @code{access?} tests the real ID, whereas an open or execute
611 attempt uses the effective ID.
613 A program which will never run set-UID/GID can ignore the difference
614 between real and effective IDs, but for maximum generality, especially
615 in library functions, it's best not to use @code{access?} to predict
616 the result of an open or execute, instead simply attempt that and
619 The main use for @code{access?} is to let a set-UID/GID program
620 determine what the invoking user would have been allowed to do,
621 without the greater (or perhaps lesser) privileges afforded by the
622 effective ID. For more on this, see @ref{Testing File Access,,, libc,
623 The GNU C Library Reference Manual}.
627 @deffn {Scheme Procedure} stat object
628 @deffnx {C Function} scm_stat (object)
629 Return an object containing various information about the file
630 determined by @var{obj}. @var{obj} can be a string containing
631 a file name or a port or integer file descriptor which is open
632 on a file (in which case @code{fstat} is used as the underlying
635 The object returned by @code{stat} can be passed as a single
636 parameter to the following procedures, all of which return
639 @deffn {Scheme Procedure} stat:dev st
640 The device number containing the file.
642 @deffn {Scheme Procedure} stat:ino st
643 The file serial number, which distinguishes this file from all
644 other files on the same device.
646 @deffn {Scheme Procedure} stat:mode st
647 The mode of the file. This is an integer which incorporates file type
648 information and file permission bits. See also @code{stat:type} and
649 @code{stat:perms} below.
651 @deffn {Scheme Procedure} stat:nlink st
652 The number of hard links to the file.
654 @deffn {Scheme Procedure} stat:uid st
655 The user ID of the file's owner.
657 @deffn {Scheme Procedure} stat:gid st
658 The group ID of the file.
660 @deffn {Scheme Procedure} stat:rdev st
661 Device ID; this entry is defined only for character or block special
662 files. On some systems this field is not available at all, in which
663 case @code{stat:rdev} returns @code{#f}.
665 @deffn {Scheme Procedure} stat:size st
666 The size of a regular file in bytes.
668 @deffn {Scheme Procedure} stat:atime st
669 The last access time for the file.
671 @deffn {Scheme Procedure} stat:mtime st
672 The last modification time for the file.
674 @deffn {Scheme Procedure} stat:ctime st
675 The last modification time for the attributes of the file.
677 @deffn {Scheme Procedure} stat:blksize st
678 The optimal block size for reading or writing the file, in bytes. On
679 some systems this field is not available, in which case
680 @code{stat:blksize} returns a sensible suggested block size.
682 @deffn {Scheme Procedure} stat:blocks st
683 The amount of disk space that the file occupies measured in units of
684 512 byte blocks. On some systems this field is not available, in
685 which case @code{stat:blocks} returns @code{#f}.
688 In addition, the following procedures return the information
689 from @code{stat:mode} in a more convenient form:
691 @deffn {Scheme Procedure} stat:type st
692 A symbol representing the type of file. Possible values are
693 @samp{regular}, @samp{directory}, @samp{symlink},
694 @samp{block-special}, @samp{char-special}, @samp{fifo}, @samp{socket},
697 @deffn {Scheme Procedure} stat:perms st
698 An integer representing the access permission bits.
702 @deffn {Scheme Procedure} lstat str
703 @deffnx {C Function} scm_lstat (str)
704 Similar to @code{stat}, but does not follow symbolic links, i.e.,
705 it will return information about a symbolic link itself, not the
706 file it points to. @var{path} must be a string.
709 @deffn {Scheme Procedure} readlink path
710 @deffnx {C Function} scm_readlink (path)
711 Return the value of the symbolic link named by @var{path} (a
712 string), i.e., the file that the link points to.
717 @deffn {Scheme Procedure} chown object owner group
718 @deffnx {C Function} scm_chown (object, owner, group)
719 Change the ownership and group of the file referred to by @var{object}
720 to the integer values @var{owner} and @var{group}. @var{object} can
721 be a string containing a file name or, if the platform supports
722 @code{fchown} (@pxref{File Owner,,,libc,The GNU C Library Reference
723 Manual}), a port or integer file descriptor which is open on the file.
724 The return value is unspecified.
726 If @var{object} is a symbolic link, either the
727 ownership of the link or the ownership of the referenced file will be
728 changed depending on the operating system (lchown is
729 unsupported at present). If @var{owner} or @var{group} is specified
730 as @code{-1}, then that ID is not changed.
734 @deffn {Scheme Procedure} chmod object mode
735 @deffnx {C Function} scm_chmod (object, mode)
736 Changes the permissions of the file referred to by @var{obj}.
737 @var{obj} can be a string containing a file name or a port or integer file
738 descriptor which is open on a file (in which case @code{fchmod} is used
739 as the underlying system call).
741 the new permissions as a decimal number, e.g., @code{(chmod "foo" #o755)}.
742 The return value is unspecified.
745 @deffn {Scheme Procedure} utime pathname [actime [modtime]]
746 @deffnx {C Function} scm_utime (pathname, actime, modtime)
748 @code{utime} sets the access and modification times for the
749 file named by @var{path}. If @var{actime} or @var{modtime} is
750 not supplied, then the current time is used. @var{actime} and
751 @var{modtime} must be integer time values as returned by the
752 @code{current-time} procedure.
754 (utime "foo" (- (current-time) 3600))
756 will set the access time to one hour in the past and the
757 modification time to the current time.
761 @deffn {Scheme Procedure} delete-file str
762 @deffnx {C Function} scm_delete_file (str)
763 Deletes (or ``unlinks'') the file whose path is specified by
767 @deffn {Scheme Procedure} copy-file oldfile newfile
768 @deffnx {C Function} scm_copy_file (oldfile, newfile)
769 Copy the file specified by @var{oldfile} to @var{newfile}.
770 The return value is unspecified.
774 @deffn {Scheme Procedure} rename-file oldname newname
775 @deffnx {C Function} scm_rename (oldname, newname)
776 Renames the file specified by @var{oldname} to @var{newname}.
777 The return value is unspecified.
780 @deffn {Scheme Procedure} link oldpath newpath
781 @deffnx {C Function} scm_link (oldpath, newpath)
782 Creates a new name @var{newpath} in the file system for the
783 file named by @var{oldpath}. If @var{oldpath} is a symbolic
784 link, the link may or may not be followed depending on the
788 @deffn {Scheme Procedure} symlink oldpath newpath
789 @deffnx {C Function} scm_symlink (oldpath, newpath)
790 Create a symbolic link named @var{newpath} with the value (i.e., pointing to)
791 @var{oldpath}. The return value is unspecified.
794 @deffn {Scheme Procedure} mkdir path [mode]
795 @deffnx {C Function} scm_mkdir (path, mode)
796 Create a new directory named by @var{path}. If @var{mode} is omitted
797 then the permissions of the directory file are set using the current
798 umask (@pxref{Processes}). Otherwise they are set to the decimal
799 value specified with @var{mode}. The return value is unspecified.
802 @deffn {Scheme Procedure} rmdir path
803 @deffnx {C Function} scm_rmdir (path)
804 Remove the existing directory named by @var{path}. The directory must
805 be empty for this to succeed. The return value is unspecified.
808 @deffn {Scheme Procedure} opendir dirname
809 @deffnx {C Function} scm_opendir (dirname)
810 @cindex directory contents
811 Open the directory specified by @var{dirname} and return a directory
815 @deffn {Scheme Procedure} directory-stream? object
816 @deffnx {C Function} scm_directory_stream_p (object)
817 Return a boolean indicating whether @var{object} is a directory
818 stream as returned by @code{opendir}.
821 @deffn {Scheme Procedure} readdir stream
822 @deffnx {C Function} scm_readdir (stream)
823 Return (as a string) the next directory entry from the directory stream
824 @var{stream}. If there is no remaining entry to be read then the
825 end of file object is returned.
828 @deffn {Scheme Procedure} rewinddir stream
829 @deffnx {C Function} scm_rewinddir (stream)
830 Reset the directory port @var{stream} so that the next call to
831 @code{readdir} will return the first directory entry.
834 @deffn {Scheme Procedure} closedir stream
835 @deffnx {C Function} scm_closedir (stream)
836 Close the directory stream @var{stream}.
837 The return value is unspecified.
840 Here is an example showing how to display all the entries in a
844 (define dir (opendir "/usr/lib"))
845 (do ((entry (readdir dir) (readdir dir)))
846 ((eof-object? entry))
847 (display entry)(newline))
851 @deffn {Scheme Procedure} sync
852 @deffnx {C Function} scm_sync ()
853 Flush the operating system disk buffers.
854 The return value is unspecified.
857 @deffn {Scheme Procedure} mknod path type perms dev
858 @deffnx {C Function} scm_mknod (path, type, perms, dev)
860 Creates a new special file, such as a file corresponding to a device.
861 @var{path} specifies the name of the file. @var{type} should be one
862 of the following symbols: @samp{regular}, @samp{directory},
863 @samp{symlink}, @samp{block-special}, @samp{char-special},
864 @samp{fifo}, or @samp{socket}. @var{perms} (an integer) specifies the
865 file permissions. @var{dev} (an integer) specifies which device the
866 special file refers to. Its exact interpretation depends on the kind
867 of special file being created.
871 (mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))
874 The return value is unspecified.
877 @deffn {Scheme Procedure} tmpnam
878 @deffnx {C Function} scm_tmpnam ()
879 @cindex temporary file
880 Return a name in the file system that does not match any
881 existing file. However there is no guarantee that another
882 process will not create the file after @code{tmpnam} is called.
883 Care should be taken if opening the file, e.g., use the
884 @code{O_EXCL} open flag or use @code{mkstemp!} instead.
887 @deffn {Scheme Procedure} mkstemp! tmpl
888 @deffnx {C Function} scm_mkstemp (tmpl)
889 @cindex temporary file
890 Create a new unique file in the file system and returns a new
891 buffered port open for reading and writing to the file.
893 @var{tmpl} is a string specifying where the file should be
894 created: it must end with @samp{XXXXXX} and will be changed in
895 place to return the name of the temporary file.
897 The file is created with mode @code{0600}, which means read and write
898 for the owner only. @code{chmod} can be used to change this.
901 @deffn {Scheme Procedure} dirname filename
902 @deffnx {C Function} scm_dirname (filename)
903 Return the directory name component of the file name
904 @var{filename}. If @var{filename} does not contain a directory
905 component, @code{.} is returned.
908 @deffn {Scheme Procedure} basename filename [suffix]
909 @deffnx {C Function} scm_basename (filename, suffix)
910 Return the base name of the file name @var{filename}. The
911 base name is the file name without any directory components.
912 If @var{suffix} is provided, and is equal to the end of
913 @var{basename}, it is removed also.
916 (basename "/tmp/test.xml" ".xml")
922 @node User Information
923 @subsection User Information
924 @cindex user information
925 @cindex password file
928 The facilities in this section provide an interface to the user and
930 They should be used with care since they are not reentrant.
932 The following functions accept an object representing user information
933 and return a selected component:
935 @deffn {Scheme Procedure} passwd:name pw
936 The name of the userid.
938 @deffn {Scheme Procedure} passwd:passwd pw
939 The encrypted passwd.
941 @deffn {Scheme Procedure} passwd:uid pw
944 @deffn {Scheme Procedure} passwd:gid pw
947 @deffn {Scheme Procedure} passwd:gecos pw
950 @deffn {Scheme Procedure} passwd:dir pw
953 @deffn {Scheme Procedure} passwd:shell pw
958 @deffn {Scheme Procedure} getpwuid uid
959 Look up an integer userid in the user database.
962 @deffn {Scheme Procedure} getpwnam name
963 Look up a user name string in the user database.
966 @deffn {Scheme Procedure} setpwent
967 Initializes a stream used by @code{getpwent} to read from the user database.
968 The next use of @code{getpwent} will return the first entry. The
969 return value is unspecified.
972 @deffn {Scheme Procedure} getpwent
973 Return the next entry in the user database, using the stream set by
977 @deffn {Scheme Procedure} endpwent
978 Closes the stream used by @code{getpwent}. The return value is unspecified.
981 @deffn {Scheme Procedure} setpw [arg]
982 @deffnx {C Function} scm_setpwent (arg)
983 If called with a true argument, initialize or reset the password data
984 stream. Otherwise, close the stream. The @code{setpwent} and
985 @code{endpwent} procedures are implemented on top of this.
988 @deffn {Scheme Procedure} getpw [user]
989 @deffnx {C Function} scm_getpwuid (user)
990 Look up an entry in the user database. @var{obj} can be an integer,
991 a string, or omitted, giving the behaviour of getpwuid, getpwnam
992 or getpwent respectively.
995 The following functions accept an object representing group information
996 and return a selected component:
998 @deffn {Scheme Procedure} group:name gr
1001 @deffn {Scheme Procedure} group:passwd gr
1002 The encrypted group password.
1004 @deffn {Scheme Procedure} group:gid gr
1005 The group id number.
1007 @deffn {Scheme Procedure} group:mem gr
1008 A list of userids which have this group as a supplementary group.
1012 @deffn {Scheme Procedure} getgrgid gid
1013 Look up an integer group id in the group database.
1016 @deffn {Scheme Procedure} getgrnam name
1017 Look up a group name in the group database.
1020 @deffn {Scheme Procedure} setgrent
1021 Initializes a stream used by @code{getgrent} to read from the group database.
1022 The next use of @code{getgrent} will return the first entry.
1023 The return value is unspecified.
1026 @deffn {Scheme Procedure} getgrent
1027 Return the next entry in the group database, using the stream set by
1031 @deffn {Scheme Procedure} endgrent
1032 Closes the stream used by @code{getgrent}.
1033 The return value is unspecified.
1036 @deffn {Scheme Procedure} setgr [arg]
1037 @deffnx {C Function} scm_setgrent (arg)
1038 If called with a true argument, initialize or reset the group data
1039 stream. Otherwise, close the stream. The @code{setgrent} and
1040 @code{endgrent} procedures are implemented on top of this.
1043 @deffn {Scheme Procedure} getgr [name]
1044 @deffnx {C Function} scm_getgrgid (name)
1045 Look up an entry in the group database. @var{obj} can be an integer,
1046 a string, or omitted, giving the behaviour of getgrgid, getgrnam
1047 or getgrent respectively.
1050 In addition to the accessor procedures for the user database, the
1051 following shortcut procedures are also available.
1053 @deffn {Scheme Procedure} cuserid
1054 @deffnx {C Function} scm_cuserid ()
1055 Return a string containing a user name associated with the
1056 effective user id of the process. Return @code{#f} if this
1057 information cannot be obtained.
1059 This function has been removed from the latest POSIX specification,
1060 Guile provides it only if the system has it. Using @code{(getpwuid
1061 (geteuid))} may be a better idea.
1064 @deffn {Scheme Procedure} getlogin
1065 @deffnx {C Function} scm_getlogin ()
1066 Return a string containing the name of the user logged in on
1067 the controlling terminal of the process, or @code{#f} if this
1068 information cannot be obtained.
1076 @deffn {Scheme Procedure} current-time
1077 @deffnx {C Function} scm_current_time ()
1078 Return the number of seconds since 1970-01-01 00:00:00 @acronym{UTC},
1079 excluding leap seconds.
1082 @deffn {Scheme Procedure} gettimeofday
1083 @deffnx {C Function} scm_gettimeofday ()
1084 Return a pair containing the number of seconds and microseconds
1085 since 1970-01-01 00:00:00 @acronym{UTC}, excluding leap seconds. Note:
1086 whether true microsecond resolution is available depends on the
1090 The following procedures either accept an object representing a broken down
1091 time and return a selected component, or accept an object representing
1092 a broken down time and a value and set the component to the value.
1093 The numbers in parentheses give the usual range.
1095 @deffn {Scheme Procedure} tm:sec tm
1096 @deffnx {Scheme Procedure} set-tm:sec tm val
1099 @deffn {Scheme Procedure} tm:min tm
1100 @deffnx {Scheme Procedure} set-tm:min tm val
1103 @deffn {Scheme Procedure} tm:hour tm
1104 @deffnx {Scheme Procedure} set-tm:hour tm val
1107 @deffn {Scheme Procedure} tm:mday tm
1108 @deffnx {Scheme Procedure} set-tm:mday tm val
1109 Day of the month (1-31).
1111 @deffn {Scheme Procedure} tm:mon tm
1112 @deffnx {Scheme Procedure} set-tm:mon tm val
1115 @deffn {Scheme Procedure} tm:year tm
1116 @deffnx {Scheme Procedure} set-tm:year tm val
1117 Year (70-), the year minus 1900.
1119 @deffn {Scheme Procedure} tm:wday tm
1120 @deffnx {Scheme Procedure} set-tm:wday tm val
1121 Day of the week (0-6) with Sunday represented as 0.
1123 @deffn {Scheme Procedure} tm:yday tm
1124 @deffnx {Scheme Procedure} set-tm:yday tm val
1125 Day of the year (0-364, 365 in leap years).
1127 @deffn {Scheme Procedure} tm:isdst tm
1128 @deffnx {Scheme Procedure} set-tm:isdst tm val
1129 Daylight saving indicator (0 for ``no'', greater than 0 for ``yes'', less than
1132 @deffn {Scheme Procedure} tm:gmtoff tm
1133 @deffnx {Scheme Procedure} set-tm:gmtoff tm val
1134 Time zone offset in seconds west of @acronym{UTC} (-46800 to 43200).
1136 @deffn {Scheme Procedure} tm:zone tm
1137 @deffnx {Scheme Procedure} set-tm:zone tm val
1138 Time zone label (a string), not necessarily unique.
1142 @deffn {Scheme Procedure} localtime time [zone]
1143 @deffnx {C Function} scm_localtime (time, zone)
1145 Return an object representing the broken down components of
1146 @var{time}, an integer like the one returned by
1147 @code{current-time}. The time zone for the calculation is
1148 optionally specified by @var{zone} (a string), otherwise the
1149 @env{TZ} environment variable or the system default is used.
1152 @deffn {Scheme Procedure} gmtime time
1153 @deffnx {C Function} scm_gmtime (time)
1154 Return an object representing the broken down components of
1155 @var{time}, an integer like the one returned by
1156 @code{current-time}. The values are calculated for @acronym{UTC}.
1159 @deffn {Scheme Procedure} mktime sbd-time [zone]
1160 @deffnx {C Function} scm_mktime (sbd_time, zone)
1161 For a broken down time object @var{sbd-time}, return a pair the
1162 @code{car} of which is an integer time like @code{current-time}, and
1163 the @code{cdr} of which is a new broken down time with normalized
1166 @var{zone} is a timezone string, or the default is the @env{TZ}
1167 environment variable or the system default (@pxref{TZ Variable,,
1168 Specifying the Time Zone with @env{TZ}, libc, GNU C Library Reference
1169 Manual}). @var{sbd-time} is taken to be in that @var{zone}.
1171 The following fields of @var{sbd-time} are used: @code{tm:year},
1172 @code{tm:mon}, @code{tm:mday}, @code{tm:hour}, @code{tm:min},
1173 @code{tm:sec}, @code{tm:isdst}. The values can be outside their usual
1174 ranges. For example @code{tm:hour} normally goes up to 23, but a
1175 value say 33 would mean 9 the following day.
1177 @code{tm:isdst} in @var{sbd-time} says whether the time given is with
1178 daylight savings or not. This is ignored if @var{zone} doesn't have
1179 any daylight savings adjustment amount.
1181 The broken down time in the return normalizes the values of
1182 @var{sbd-time} by bringing them into their usual ranges, and using the
1183 actual daylight savings rule for that time in @var{zone} (which may
1184 differ from what @var{sbd-time} had). The easiest way to think of
1185 this is that @var{sbd-time} plus @var{zone} converts to the integer
1186 UTC time, then a @code{localtime} is applied to get the normal
1187 presentation of that time, in @var{zone}.
1190 @deffn {Scheme Procedure} tzset
1191 @deffnx {C Function} scm_tzset ()
1192 Initialize the timezone from the @env{TZ} environment variable
1193 or the system default. It's not usually necessary to call this procedure
1194 since it's done automatically by other procedures that depend on the
1198 @deffn {Scheme Procedure} strftime format stime
1199 @deffnx {C Function} scm_strftime (format, stime)
1200 @cindex time formatting
1201 Formats a time specification @var{time} using @var{template}. @var{time}
1202 is an object with time components in the form returned by @code{localtime}
1203 or @code{gmtime}. @var{template} is a string which can include formatting
1204 specifications introduced by a @samp{%} character. The formatting of
1205 month and day names is dependent on the current locale. The value returned
1206 is the formatted string.
1207 @xref{Formatting Calendar Time, , , libc, The GNU C Library Reference Manual}.
1210 (strftime "%c" (localtime (current-time)))
1211 @result{} "Mon Mar 11 20:17:43 2002"
1215 @deffn {Scheme Procedure} strptime format string
1216 @deffnx {C Function} scm_strptime (format, string)
1217 @cindex time parsing
1218 Performs the reverse action to @code{strftime}, parsing
1219 @var{string} according to the specification supplied in
1220 @var{template}. The interpretation of month and day names is
1221 dependent on the current locale. The value returned is a pair.
1222 The @acronym{CAR} has an object with time components
1223 in the form returned by @code{localtime} or @code{gmtime},
1224 but the time zone components
1225 are not usefully set.
1226 The @acronym{CDR} reports the number of characters from @var{string}
1227 which were used for the conversion.
1230 @defvar internal-time-units-per-second
1231 The value of this variable is the number of time units per second
1232 reported by the following procedures.
1235 @deffn {Scheme Procedure} times
1236 @deffnx {C Function} scm_times ()
1237 Return an object with information about real and processor
1238 time. The following procedures accept such an object as an
1239 argument and return a selected component:
1241 @deffn {Scheme Procedure} tms:clock tms
1242 The current real time, expressed as time units relative to an
1245 @deffn {Scheme Procedure} tms:utime tms
1246 The CPU time units used by the calling process.
1248 @deffn {Scheme Procedure} tms:stime tms
1249 The CPU time units used by the system on behalf of the calling
1252 @deffn {Scheme Procedure} tms:cutime tms
1253 The CPU time units used by terminated child processes of the
1254 calling process, whose status has been collected (e.g., using
1257 @deffn {Scheme Procedure} tms:cstime tms
1258 Similarly, the CPU times units used by the system on behalf of
1259 terminated child processes.
1263 @deffn {Scheme Procedure} get-internal-real-time
1264 @deffnx {C Function} scm_get_internal_real_time ()
1265 Return the number of time units since the interpreter was
1269 @deffn {Scheme Procedure} get-internal-run-time
1270 @deffnx {C Function} scm_get_internal_run_time ()
1271 Return the number of time units of processor time used by the
1272 interpreter. Both @emph{system} and @emph{user} time are
1273 included but subprocesses are not.
1276 @node Runtime Environment
1277 @subsection Runtime Environment
1279 @deffn {Scheme Procedure} program-arguments
1280 @deffnx {Scheme Procedure} command-line
1281 @deffnx {C Function} scm_program_arguments ()
1282 @cindex command line
1283 @cindex program arguments
1284 Return the list of command line arguments passed to Guile, as a list of
1285 strings. The list includes the invoked program name, which is usually
1286 @code{"guile"}, but excludes switches and parameters for command line
1287 options like @code{-e} and @code{-l}.
1290 @deffn {Scheme Procedure} getenv nam
1291 @deffnx {C Function} scm_getenv (nam)
1293 Looks up the string @var{name} in the current environment. The return
1294 value is @code{#f} unless a string of the form @code{NAME=VALUE} is
1295 found, in which case the string @code{VALUE} is returned.
1298 @deffn {Scheme Procedure} setenv name value
1299 Modifies the environment of the current process, which is
1300 also the default environment inherited by child processes.
1302 If @var{value} is @code{#f}, then @var{name} is removed from the
1303 environment. Otherwise, the string @var{name}=@var{value} is added
1304 to the environment, replacing any existing string with name matching
1307 The return value is unspecified.
1310 @deffn {Scheme Procedure} unsetenv name
1311 Remove variable @var{name} from the environment. The
1312 name can not contain a @samp{=} character.
1315 @deffn {Scheme Procedure} environ [env]
1316 @deffnx {C Function} scm_environ (env)
1317 If @var{env} is omitted, return the current environment (in the
1318 Unix sense) as a list of strings. Otherwise set the current
1319 environment, which is also the default environment for child
1320 processes, to the supplied list of strings. Each member of
1321 @var{env} should be of the form @var{NAME}=@var{VALUE} and values of
1322 @var{NAME} should not be duplicated. If @var{env} is supplied
1323 then the return value is unspecified.
1326 @deffn {Scheme Procedure} putenv str
1327 @deffnx {C Function} scm_putenv (str)
1328 Modifies the environment of the current process, which is
1329 also the default environment inherited by child processes.
1331 If @var{string} is of the form @code{NAME=VALUE} then it will be written
1332 directly into the environment, replacing any existing environment string
1334 name matching @code{NAME}. If @var{string} does not contain an equal
1335 sign, then any existing string with name matching @var{string} will
1338 The return value is unspecified.
1343 @subsection Processes
1345 @cindex child processes
1348 @deffn {Scheme Procedure} chdir str
1349 @deffnx {C Function} scm_chdir (str)
1350 @cindex current directory
1351 Change the current working directory to @var{path}.
1352 The return value is unspecified.
1356 @deffn {Scheme Procedure} getcwd
1357 @deffnx {C Function} scm_getcwd ()
1358 Return the name of the current working directory.
1361 @deffn {Scheme Procedure} umask [mode]
1362 @deffnx {C Function} scm_umask (mode)
1363 If @var{mode} is omitted, returns a decimal number representing the
1364 current file creation mask. Otherwise the file creation mask is set
1365 to @var{mode} and the previous value is returned. @xref{Setting
1366 Permissions,,Assigning File Permissions,libc,The GNU C Library
1367 Reference Manual}, for more on how to use umasks.
1369 E.g., @code{(umask #o022)} sets the mask to octal 22/decimal 18.
1372 @deffn {Scheme Procedure} chroot path
1373 @deffnx {C Function} scm_chroot (path)
1374 Change the root directory to that specified in @var{path}.
1375 This directory will be used for path names beginning with
1376 @file{/}. The root directory is inherited by all children
1377 of the current process. Only the superuser may change the
1381 @deffn {Scheme Procedure} getpid
1382 @deffnx {C Function} scm_getpid ()
1383 Return an integer representing the current process ID.
1386 @deffn {Scheme Procedure} getgroups
1387 @deffnx {C Function} scm_getgroups ()
1388 Return a vector of integers representing the current
1389 supplementary group IDs.
1392 @deffn {Scheme Procedure} getppid
1393 @deffnx {C Function} scm_getppid ()
1394 Return an integer representing the process ID of the parent
1398 @deffn {Scheme Procedure} getuid
1399 @deffnx {C Function} scm_getuid ()
1400 Return an integer representing the current real user ID.
1403 @deffn {Scheme Procedure} getgid
1404 @deffnx {C Function} scm_getgid ()
1405 Return an integer representing the current real group ID.
1408 @deffn {Scheme Procedure} geteuid
1409 @deffnx {C Function} scm_geteuid ()
1410 Return an integer representing the current effective user ID.
1411 If the system does not support effective IDs, then the real ID
1412 is returned. @code{(provided? 'EIDs)} reports whether the
1413 system supports effective IDs.
1416 @deffn {Scheme Procedure} getegid
1417 @deffnx {C Function} scm_getegid ()
1418 Return an integer representing the current effective group ID.
1419 If the system does not support effective IDs, then the real ID
1420 is returned. @code{(provided? 'EIDs)} reports whether the
1421 system supports effective IDs.
1424 @deffn {Scheme Procedure} setgroups vec
1425 @deffnx {C Function} scm_setgroups (vec)
1426 Set the current set of supplementary group IDs to the integers in the
1427 given vector @var{vec}. The return value is unspecified.
1429 Generally only the superuser can set the process group IDs
1430 (@pxref{Setting Groups, Setting the Group IDs,, libc, The GNU C
1431 Library Reference Manual}).
1434 @deffn {Scheme Procedure} setuid id
1435 @deffnx {C Function} scm_setuid (id)
1436 Sets both the real and effective user IDs to the integer @var{id}, provided
1437 the process has appropriate privileges.
1438 The return value is unspecified.
1441 @deffn {Scheme Procedure} setgid id
1442 @deffnx {C Function} scm_setgid (id)
1443 Sets both the real and effective group IDs to the integer @var{id}, provided
1444 the process has appropriate privileges.
1445 The return value is unspecified.
1448 @deffn {Scheme Procedure} seteuid id
1449 @deffnx {C Function} scm_seteuid (id)
1450 Sets the effective user ID to the integer @var{id}, provided the process
1451 has appropriate privileges. If effective IDs are not supported, the
1452 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1453 system supports effective IDs.
1454 The return value is unspecified.
1457 @deffn {Scheme Procedure} setegid id
1458 @deffnx {C Function} scm_setegid (id)
1459 Sets the effective group ID to the integer @var{id}, provided the process
1460 has appropriate privileges. If effective IDs are not supported, the
1461 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1462 system supports effective IDs.
1463 The return value is unspecified.
1466 @deffn {Scheme Procedure} getpgrp
1467 @deffnx {C Function} scm_getpgrp ()
1468 Return an integer representing the current process group ID.
1469 This is the @acronym{POSIX} definition, not @acronym{BSD}.
1472 @deffn {Scheme Procedure} setpgid pid pgid
1473 @deffnx {C Function} scm_setpgid (pid, pgid)
1474 Move the process @var{pid} into the process group @var{pgid}. @var{pid} or
1475 @var{pgid} must be integers: they can be zero to indicate the ID of the
1477 Fails on systems that do not support job control.
1478 The return value is unspecified.
1481 @deffn {Scheme Procedure} setsid
1482 @deffnx {C Function} scm_setsid ()
1483 Creates a new session. The current process becomes the session leader
1484 and is put in a new process group. The process will be detached
1485 from its controlling terminal if it has one.
1486 The return value is an integer representing the new process group ID.
1489 @deffn {Scheme Procedure} waitpid pid [options]
1490 @deffnx {C Function} scm_waitpid (pid, options)
1491 This procedure collects status information from a child process which
1492 has terminated or (optionally) stopped. Normally it will
1493 suspend the calling process until this can be done. If more than one
1494 child process is eligible then one will be chosen by the operating system.
1496 The value of @var{pid} determines the behaviour:
1499 @item @var{pid} greater than 0
1500 Request status information from the specified child process.
1501 @item @var{pid} equal to -1 or @code{WAIT_ANY}
1503 Request status information for any child process.
1504 @item @var{pid} equal to 0 or @code{WAIT_MYPGRP}
1506 Request status information for any child process in the current process
1508 @item @var{pid} less than -1
1509 Request status information for any child process whose process group ID
1510 is @minus{}@var{pid}.
1513 The @var{options} argument, if supplied, should be the bitwise OR of the
1514 values of zero or more of the following variables:
1517 Return immediately even if there are no child processes to be collected.
1521 Report status information for stopped processes as well as terminated
1525 The return value is a pair containing:
1529 The process ID of the child process, or 0 if @code{WNOHANG} was
1530 specified and no process was collected.
1532 The integer status value.
1537 functions can be used to decode the process status code returned
1540 @deffn {Scheme Procedure} status:exit-val status
1541 @deffnx {C Function} scm_status_exit_val (status)
1542 Return the exit status value, as would be set if a process
1543 ended normally through a call to @code{exit} or @code{_exit},
1544 if any, otherwise @code{#f}.
1547 @deffn {Scheme Procedure} status:term-sig status
1548 @deffnx {C Function} scm_status_term_sig (status)
1549 Return the signal number which terminated the process, if any,
1550 otherwise @code{#f}.
1553 @deffn {Scheme Procedure} status:stop-sig status
1554 @deffnx {C Function} scm_status_stop_sig (status)
1555 Return the signal number which stopped the process, if any,
1556 otherwise @code{#f}.
1559 @deffn {Scheme Procedure} system [cmd]
1560 @deffnx {C Function} scm_system (cmd)
1561 Execute @var{cmd} using the operating system's ``command
1562 processor''. Under Unix this is usually the default shell
1563 @code{sh}. The value returned is @var{cmd}'s exit status as
1564 returned by @code{waitpid}, which can be interpreted using the
1567 If @code{system} is called without arguments, return a boolean
1568 indicating whether the command processor is available.
1571 @deffn {Scheme Procedure} system* . args
1572 @deffnx {C Function} scm_system_star (args)
1573 Execute the command indicated by @var{args}. The first element must
1574 be a string indicating the command to be executed, and the remaining
1575 items must be strings representing each of the arguments to that
1578 This function returns the exit status of the command as provided by
1579 @code{waitpid}. This value can be handled with @code{status:exit-val}
1580 and the related functions.
1582 @code{system*} is similar to @code{system}, but accepts only one
1583 string per-argument, and performs no shell interpretation. The
1584 command is executed using fork and execlp. Accordingly this function
1585 may be safer than @code{system} in situations where shell
1586 interpretation is not required.
1588 Example: (system* "echo" "foo" "bar")
1591 @deffn {Scheme Procedure} primitive-exit [status]
1592 @deffnx {C Function} scm_primitive_exit (status)
1593 Terminate the current process without unwinding the Scheme stack.
1594 This is would typically be useful after a fork. The exit status
1595 is @var{status} if supplied, otherwise zero.
1598 @deffn {Scheme Procedure} execl filename . args
1599 @deffnx {C Function} scm_execl (filename, args)
1600 Executes the file named by @var{path} as a new process image.
1601 The remaining arguments are supplied to the process; from a C program
1602 they are accessible as the @code{argv} argument to @code{main}.
1603 Conventionally the first @var{arg} is the same as @var{path}.
1604 All arguments must be strings.
1606 If @var{arg} is missing, @var{path} is executed with a null
1607 argument list, which may have system-dependent side-effects.
1609 This procedure is currently implemented using the @code{execv} system
1610 call, but we call it @code{execl} because of its Scheme calling interface.
1613 @deffn {Scheme Procedure} execlp filename . args
1614 @deffnx {C Function} scm_execlp (filename, args)
1615 Similar to @code{execl}, however if
1616 @var{filename} does not contain a slash
1617 then the file to execute will be located by searching the
1618 directories listed in the @code{PATH} environment variable.
1620 This procedure is currently implemented using the @code{execvp} system
1621 call, but we call it @code{execlp} because of its Scheme calling interface.
1624 @deffn {Scheme Procedure} execle filename env . args
1625 @deffnx {C Function} scm_execle (filename, env, args)
1626 Similar to @code{execl}, but the environment of the new process is
1627 specified by @var{env}, which must be a list of strings as returned by the
1628 @code{environ} procedure.
1630 This procedure is currently implemented using the @code{execve} system
1631 call, but we call it @code{execle} because of its Scheme calling interface.
1634 @deffn {Scheme Procedure} primitive-fork
1635 @deffnx {C Function} scm_fork ()
1636 Creates a new ``child'' process by duplicating the current ``parent'' process.
1637 In the child the return value is 0. In the parent the return value is
1638 the integer process ID of the child.
1640 This procedure has been renamed from @code{fork} to avoid a naming conflict
1644 @deffn {Scheme Procedure} nice incr
1645 @deffnx {C Function} scm_nice (incr)
1646 @cindex process priority
1647 Increment the priority of the current process by @var{incr}. A higher
1648 priority value means that the process runs less often.
1649 The return value is unspecified.
1652 @deffn {Scheme Procedure} setpriority which who prio
1653 @deffnx {C Function} scm_setpriority (which, who, prio)
1654 @vindex PRIO_PROCESS
1657 Set the scheduling priority of the process, process group
1658 or user, as indicated by @var{which} and @var{who}. @var{which}
1659 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1660 or @code{PRIO_USER}, and @var{who} is interpreted relative to
1661 @var{which} (a process identifier for @code{PRIO_PROCESS},
1662 process group identifier for @code{PRIO_PGRP}, and a user
1663 identifier for @code{PRIO_USER}. A zero value of @var{who}
1664 denotes the current process, process group, or user.
1665 @var{prio} is a value in the range [@minus{}20,20]. The default
1666 priority is 0; lower priorities (in numerical terms) cause more
1667 favorable scheduling. Sets the priority of all of the specified
1668 processes. Only the super-user may lower priorities. The return
1669 value is not specified.
1672 @deffn {Scheme Procedure} getpriority which who
1673 @deffnx {C Function} scm_getpriority (which, who)
1674 @vindex PRIO_PROCESS
1677 Return the scheduling priority of the process, process group
1678 or user, as indicated by @var{which} and @var{who}. @var{which}
1679 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1680 or @code{PRIO_USER}, and @var{who} should be interpreted depending on
1681 @var{which} (a process identifier for @code{PRIO_PROCESS},
1682 process group identifier for @code{PRIO_PGRP}, and a user
1683 identifier for @code{PRIO_USER}). A zero value of @var{who}
1684 denotes the current process, process group, or user. Return
1685 the highest priority (lowest numerical value) of any of the
1686 specified processes.
1694 Procedures to raise, handle and wait for signals.
1696 @deffn {Scheme Procedure} kill pid sig
1697 @deffnx {C Function} scm_kill (pid, sig)
1698 Sends a signal to the specified process or group of processes.
1700 @var{pid} specifies the processes to which the signal is sent:
1703 @item @var{pid} greater than 0
1704 The process whose identifier is @var{pid}.
1705 @item @var{pid} equal to 0
1706 All processes in the current process group.
1707 @item @var{pid} less than -1
1708 The process group whose identifier is -@var{pid}
1709 @item @var{pid} equal to -1
1710 If the process is privileged, all processes except for some special
1711 system processes. Otherwise, all processes with the current effective
1715 @var{sig} should be specified using a variable corresponding to
1716 the Unix symbolic name, e.g.,
1726 A full list of signals on the GNU system may be found in @ref{Standard
1727 Signals,,,libc,The GNU C Library Reference Manual}.
1730 @deffn {Scheme Procedure} raise sig
1731 @deffnx {C Function} scm_raise (sig)
1732 Sends a specified signal @var{sig} to the current process, where
1733 @var{sig} is as described for the @code{kill} procedure.
1736 @deffn {Scheme Procedure} sigaction signum [handler [flags [thread]]]
1737 @deffnx {C Function} scm_sigaction (signum, handler, flags)
1738 @deffnx {C Function} scm_sigaction_for_thread (signum, handler, flags, thread)
1739 Install or report the signal handler for a specified signal.
1741 @var{signum} is the signal number, which can be specified using the value
1742 of variables such as @code{SIGINT}.
1744 If @var{handler} is omitted, @code{sigaction} returns a pair: the
1745 @acronym{CAR} is the current signal hander, which will be either an
1746 integer with the value @code{SIG_DFL} (default action) or
1747 @code{SIG_IGN} (ignore), or the Scheme procedure which handles the
1748 signal, or @code{#f} if a non-Scheme procedure handles the signal.
1749 The @acronym{CDR} contains the current @code{sigaction} flags for the
1752 If @var{handler} is provided, it is installed as the new handler for
1753 @var{signum}. @var{handler} can be a Scheme procedure taking one
1754 argument, or the value of @code{SIG_DFL} (default action) or
1755 @code{SIG_IGN} (ignore), or @code{#f} to restore whatever signal handler
1756 was installed before @code{sigaction} was first used. When a scheme
1757 procedure has been specified, that procedure will run in the given
1758 @var{thread}. When no thread has been given, the thread that made this
1759 call to @code{sigaction} is used.
1761 @var{flags} is a @code{logior} (@pxref{Bitwise Operations}) of the
1762 following (where provided by the system), or @code{0} for none.
1764 @defvar SA_NOCLDSTOP
1765 By default, @code{SIGCHLD} is signalled when a child process stops
1766 (ie.@: receives @code{SIGSTOP}), and when a child process terminates.
1767 With the @code{SA_NOCLDSTOP} flag, @code{SIGCHLD} is only signalled
1768 for termination, not stopping.
1770 @code{SA_NOCLDSTOP} has no effect on signals other than
1775 If a signal occurs while in a system call, deliver the signal then
1776 restart the system call (as opposed to returning an @code{EINTR} error
1779 Guile always enables this flag where available, no matter what
1780 @var{flags} are specified. This avoids spurious error returns in low
1784 The return value is a pair with information about the old handler as
1787 This interface does not provide access to the ``signal blocking''
1788 facility. Maybe this is not needed, since the thread support may
1789 provide solutions to the problem of consistent access to data
1793 @deffn {Scheme Procedure} restore-signals
1794 @deffnx {C Function} scm_restore_signals ()
1795 Return all signal handlers to the values they had before any call to
1796 @code{sigaction} was made. The return value is unspecified.
1799 @deffn {Scheme Procedure} alarm i
1800 @deffnx {C Function} scm_alarm (i)
1801 Set a timer to raise a @code{SIGALRM} signal after the specified
1802 number of seconds (an integer). It's advisable to install a signal
1804 @code{SIGALRM} beforehand, since the default action is to terminate
1807 The return value indicates the time remaining for the previous alarm,
1808 if any. The new value replaces the previous alarm. If there was
1809 no previous alarm, the return value is zero.
1812 @deffn {Scheme Procedure} pause
1813 @deffnx {C Function} scm_pause ()
1814 Pause the current process (thread?) until a signal arrives whose
1815 action is to either terminate the current process or invoke a
1816 handler procedure. The return value is unspecified.
1819 @deffn {Scheme Procedure} sleep i
1820 @deffnx {C Function} scm_sleep (i)
1821 Wait for the given number of seconds (an integer) or until a signal
1822 arrives. The return value is zero if the time elapses or the number
1823 of seconds remaining otherwise.
1826 @deffn {Scheme Procedure} usleep i
1827 @deffnx {C Function} scm_usleep (i)
1828 Sleep for @var{i} microseconds. @code{usleep} is not available on
1829 all platforms. [FIXME: so what happens when it isn't?]
1832 @deffn {Scheme Procedure} setitimer which_timer interval_seconds interval_microseconds value_seconds value_microseconds
1833 @deffnx {C Function} scm_setitimer (which_timer, interval_seconds, interval_microseconds, value_seconds, value_microseconds)
1834 Set the timer specified by @var{which_timer} according to the given
1835 @var{interval_seconds}, @var{interval_microseconds},
1836 @var{value_seconds}, and @var{value_microseconds} values.
1838 Return information about the timer's previous setting.
1840 The timers available are: @code{ITIMER_REAL}, @code{ITIMER_VIRTUAL},
1841 and @code{ITIMER_PROF}.
1843 The return value will be a list of two cons pairs representing the
1844 current state of the given timer. The first pair is the seconds and
1845 microseconds of the timer @code{it_interval}, and the second pair is
1846 the seconds and microseconds of the timer @code{it_value}.
1849 @deffn {Scheme Procedure} getitimer which_timer
1850 @deffnx {C Function} scm_getitimer (which_timer)
1851 Return information about the timer specified by @var{which_timer}.
1853 The timers available are: @code{ITIMER_REAL}, @code{ITIMER_VIRTUAL},
1854 and @code{ITIMER_PROF}.
1856 The return value will be a list of two cons pairs representing the
1857 current state of the given timer. The first pair is the seconds and
1858 microseconds of the timer @code{it_interval}, and the second pair is
1859 the seconds and microseconds of the timer @code{it_value}.
1863 @node Terminals and Ptys
1864 @subsection Terminals and Ptys
1866 @deffn {Scheme Procedure} isatty? port
1867 @deffnx {C Function} scm_isatty_p (port)
1869 Return @code{#t} if @var{port} is using a serial non--file
1870 device, otherwise @code{#f}.
1873 @deffn {Scheme Procedure} ttyname port
1874 @deffnx {C Function} scm_ttyname (port)
1876 Return a string with the name of the serial terminal device
1877 underlying @var{port}.
1880 @deffn {Scheme Procedure} ctermid
1881 @deffnx {C Function} scm_ctermid ()
1883 Return a string containing the file name of the controlling
1884 terminal for the current process.
1887 @deffn {Scheme Procedure} tcgetpgrp port
1888 @deffnx {C Function} scm_tcgetpgrp (port)
1889 @cindex process group
1890 Return the process group ID of the foreground process group
1891 associated with the terminal open on the file descriptor
1892 underlying @var{port}.
1894 If there is no foreground process group, the return value is a
1895 number greater than 1 that does not match the process group ID
1896 of any existing process group. This can happen if all of the
1897 processes in the job that was formerly the foreground job have
1898 terminated, and no other job has yet been moved into the
1902 @deffn {Scheme Procedure} tcsetpgrp port pgid
1903 @deffnx {C Function} scm_tcsetpgrp (port, pgid)
1904 @cindex process group
1905 Set the foreground process group ID for the terminal used by the file
1906 descriptor underlying @var{port} to the integer @var{pgid}.
1908 must be a member of the same session as @var{pgid} and must have the same
1909 controlling terminal. The return value is unspecified.
1916 The following procedures are similar to the @code{popen} and
1917 @code{pclose} system routines. The code is in a separate ``popen''
1921 (use-modules (ice-9 popen))
1925 @deffn {Scheme Procedure} open-pipe command mode
1926 @deffnx {Scheme Procedure} open-pipe* mode prog [args...]
1927 Execute a command in a subprocess, with a pipe to it or from it, or
1928 with pipes in both directions.
1930 @code{open-pipe} runs the shell @var{command} using @samp{/bin/sh -c}.
1931 @code{open-pipe*} executes @var{prog} directly, with the optional
1932 @var{args} arguments (all strings).
1934 @var{mode} should be one of the following values. @code{OPEN_READ} is
1935 an input pipe, ie.@: to read from the subprocess. @code{OPEN_WRITE}
1936 is an output pipe, ie.@: to write to it.
1943 For an input pipe, the child's standard output is the pipe and
1944 standard input is inherited from @code{current-input-port}. For an
1945 output pipe, the child's standard input is the pipe and standard
1946 output is inherited from @code{current-output-port}. In all cases
1947 cases the child's standard error is inherited from
1948 @code{current-error-port} (@pxref{Default Ports}).
1950 If those @code{current-X-ports} are not files of some kind, and hence
1951 don't have file descriptors for the child, then @file{/dev/null} is
1954 Care should be taken with @code{OPEN_BOTH}, a deadlock will occur if
1955 both parent and child are writing, and waiting until the write
1956 completes before doing any reading. Each direction has
1957 @code{PIPE_BUF} bytes of buffering (@pxref{Ports and File
1958 Descriptors}), which will be enough for small writes, but not for say
1959 putting a big file through a filter.
1962 @deffn {Scheme Procedure} open-input-pipe command
1963 Equivalent to @code{open-pipe} with mode @code{OPEN_READ}.
1966 (let* ((port (open-input-pipe "date --utc"))
1967 (str (read-line port)))
1970 @result{} "Mon Mar 11 20:10:44 UTC 2002"
1974 @deffn {Scheme Procedure} open-output-pipe command
1975 Equivalent to @code{open-pipe} with mode @code{OPEN_WRITE}.
1978 (let ((port (open-output-pipe "lpr")))
1979 (display "Something for the line printer.\n" port)
1980 (if (not (eqv? 0 (status:exit-val (close-pipe port))))
1981 (error "Cannot print")))
1985 @deffn {Scheme Procedure} open-input-output-pipe command
1986 Equivalent to @code{open-pipe} with mode @code{OPEN_BOTH}.
1990 @deffn {Scheme Procedure} close-pipe port
1991 Close a pipe created by @code{open-pipe}, wait for the process to
1992 terminate, and return the wait status code. The status is as per
1993 @code{waitpid} and can be decoded with @code{status:exit-val} etc
1998 @code{waitpid WAIT_ANY} should not be used when pipes are open, since
1999 it can reap a pipe's child process, causing an error from a subsequent
2002 @code{close-port} (@pxref{Closing}) can close a pipe, but it doesn't
2003 reap the child process.
2005 The garbage collector will close a pipe no longer in use, and reap the
2006 child process with @code{waitpid}. If the child hasn't yet terminated
2007 the garbage collector doesn't block, but instead checks again in the
2010 Many systems have per-user and system-wide limits on the number of
2011 processes, and a system-wide limit on the number of pipes, so pipes
2012 should be closed explicitly when no longer needed, rather than letting
2013 the garbage collector pick them up at some later time.
2017 @subsection Networking
2021 * Network Address Conversion::
2022 * Network Databases::
2023 * Network Sockets and Communication::
2024 * Internet Socket Examples::
2027 @node Network Address Conversion
2028 @subsubsection Network Address Conversion
2029 @cindex network address
2031 This section describes procedures which convert internet addresses
2032 between numeric and string formats.
2034 @subsubheading IPv4 Address Conversion
2037 An IPv4 Internet address is a 4-byte value, represented in Guile as an
2038 integer in network byte order (meaning the first byte is the most
2039 significant in the number).
2041 @defvar INADDR_LOOPBACK
2042 The address of the local host using the loopback device, ie.@:
2046 @defvar INADDR_BROADCAST
2047 The broadcast address on the local network.
2050 @c INADDR_NONE is defined in the code, but serves no purpose.
2051 @c inet_addr() returns it as an error indication, but that function
2052 @c isn't provided, for the good reason that inet_aton() does the same
2053 @c job and gives an unambiguous error indication. (INADDR_NONE is a
2054 @c valid 4-byte value, in glibc it's the same as INADDR_BROADCAST.)
2056 @c @defvar INADDR_NONE
2060 @deffn {Scheme Procedure} inet-aton address
2061 @deffnx {C Function} scm_inet_aton (address)
2062 Convert an IPv4 Internet address from printable string
2063 (dotted decimal notation) to an integer. E.g.,
2066 (inet-aton "127.0.0.1") @result{} 2130706433
2070 @deffn {Scheme Procedure} inet-ntoa inetid
2071 @deffnx {C Function} scm_inet_ntoa (inetid)
2072 Convert an IPv4 Internet address to a printable
2073 (dotted decimal notation) string. E.g.,
2076 (inet-ntoa 2130706433) @result{} "127.0.0.1"
2080 @deffn {Scheme Procedure} inet-netof address
2081 @deffnx {C Function} scm_inet_netof (address)
2082 Return the network number part of the given IPv4
2083 Internet address. E.g.,
2086 (inet-netof 2130706433) @result{} 127
2090 @deffn {Scheme Procedure} inet-lnaof address
2091 @deffnx {C Function} scm_lnaof (address)
2092 Return the local-address-with-network part of the given
2093 IPv4 Internet address, using the obsolete class A/B/C system.
2097 (inet-lnaof 2130706433) @result{} 1
2101 @deffn {Scheme Procedure} inet-makeaddr net lna
2102 @deffnx {C Function} scm_inet_makeaddr (net, lna)
2103 Make an IPv4 Internet address by combining the network number
2104 @var{net} with the local-address-within-network number
2108 (inet-makeaddr 127 1) @result{} 2130706433
2112 @subsubheading IPv6 Address Conversion
2115 @deffn {Scheme Procedure} inet-ntop family address
2116 @deffnx {C Function} scm_inet_ntop (family, address)
2117 Convert a network address into a printable string.
2118 Note that unlike the C version of this function,
2119 the input is an integer with normal host byte ordering.
2120 @var{family} can be @code{AF_INET} or @code{AF_INET6}. E.g.,
2123 (inet-ntop AF_INET 2130706433) @result{} "127.0.0.1"
2124 (inet-ntop AF_INET6 (- (expt 2 128) 1)) @result{}
2125 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
2129 @deffn {Scheme Procedure} inet-pton family address
2130 @deffnx {C Function} scm_inet_pton (family, address)
2131 Convert a string containing a printable network address to
2132 an integer address. Note that unlike the C version of this
2134 the result is an integer with normal host byte ordering.
2135 @var{family} can be @code{AF_INET} or @code{AF_INET6}. E.g.,
2138 (inet-pton AF_INET "127.0.0.1") @result{} 2130706433
2139 (inet-pton AF_INET6 "::1") @result{} 1
2144 @node Network Databases
2145 @subsubsection Network Databases
2146 @cindex network database
2148 This section describes procedures which query various network databases.
2149 Care should be taken when using the database routines since they are not
2152 @subsubheading The Host Database
2153 @cindex @file{/etc/hosts}
2154 @cindex network database
2156 A @dfn{host object} is a structure that represents what is known about a
2157 network host, and is the usual way of representing a system's network
2158 identity inside software.
2160 The following functions accept a host object and return a selected
2163 @deffn {Scheme Procedure} hostent:name host
2164 The ``official'' hostname for @var{host}.
2166 @deffn {Scheme Procedure} hostent:aliases host
2167 A list of aliases for @var{host}.
2169 @deffn {Scheme Procedure} hostent:addrtype host
2170 The host address type. For hosts with Internet addresses, this will
2171 return @code{AF_INET}.
2173 @deffn {Scheme Procedure} hostent:length host
2174 The length of each address for @var{host}, in bytes.
2176 @deffn {Scheme Procedure} hostent:addr-list host
2177 The list of network addresses associated with @var{host}.
2180 The following procedures are used to search the host database:
2182 @deffn {Scheme Procedure} gethost [host]
2183 @deffnx {Scheme Procedure} gethostbyname hostname
2184 @deffnx {Scheme Procedure} gethostbyaddr address
2185 @deffnx {C Function} scm_gethost (host)
2186 Look up a host by name or address, returning a host object. The
2187 @code{gethost} procedure will accept either a string name or an integer
2188 address; if given no arguments, it behaves like @code{gethostent} (see
2189 below). If a name or address is supplied but the address can not be
2190 found, an error will be thrown to one of the keys:
2191 @code{host-not-found}, @code{try-again}, @code{no-recovery} or
2192 @code{no-data}, corresponding to the equivalent @code{h_error} values.
2193 Unusual conditions may result in errors thrown to the
2194 @code{system-error} or @code{misc_error} keys.
2197 (gethost "www.gnu.org")
2198 @result{} #("www.gnu.org" () 2 4 (3353880842))
2200 (gethostbyname "www.emacs.org")
2201 @result{} #("emacs.org" ("www.emacs.org") 2 4 (1073448978))
2205 The following procedures may be used to step through the host
2206 database from beginning to end.
2208 @deffn {Scheme Procedure} sethostent [stayopen]
2209 Initialize an internal stream from which host objects may be read. This
2210 procedure must be called before any calls to @code{gethostent}, and may
2211 also be called afterward to reset the host entry stream. If
2212 @var{stayopen} is supplied and is not @code{#f}, the database is not
2213 closed by subsequent @code{gethostbyname} or @code{gethostbyaddr} calls,
2214 possibly giving an efficiency gain.
2217 @deffn {Scheme Procedure} gethostent
2218 Return the next host object from the host database, or @code{#f} if
2219 there are no more hosts to be found (or an error has been encountered).
2220 This procedure may not be used before @code{sethostent} has been called.
2223 @deffn {Scheme Procedure} endhostent
2224 Close the stream used by @code{gethostent}. The return value is unspecified.
2227 @deffn {Scheme Procedure} sethost [stayopen]
2228 @deffnx {C Function} scm_sethost (stayopen)
2229 If @var{stayopen} is omitted, this is equivalent to @code{endhostent}.
2230 Otherwise it is equivalent to @code{sethostent stayopen}.
2233 @subsubheading The Network Database
2234 @cindex network database
2236 The following functions accept an object representing a network
2237 and return a selected component:
2239 @deffn {Scheme Procedure} netent:name net
2240 The ``official'' network name.
2242 @deffn {Scheme Procedure} netent:aliases net
2243 A list of aliases for the network.
2245 @deffn {Scheme Procedure} netent:addrtype net
2246 The type of the network number. Currently, this returns only
2249 @deffn {Scheme Procedure} netent:net net
2253 The following procedures are used to search the network database:
2255 @deffn {Scheme Procedure} getnet [net]
2256 @deffnx {Scheme Procedure} getnetbyname net-name
2257 @deffnx {Scheme Procedure} getnetbyaddr net-number
2258 @deffnx {C Function} scm_getnet (net)
2259 Look up a network by name or net number in the network database. The
2260 @var{net-name} argument must be a string, and the @var{net-number}
2261 argument must be an integer. @code{getnet} will accept either type of
2262 argument, behaving like @code{getnetent} (see below) if no arguments are
2266 The following procedures may be used to step through the network
2267 database from beginning to end.
2269 @deffn {Scheme Procedure} setnetent [stayopen]
2270 Initialize an internal stream from which network objects may be read. This
2271 procedure must be called before any calls to @code{getnetent}, and may
2272 also be called afterward to reset the net entry stream. If
2273 @var{stayopen} is supplied and is not @code{#f}, the database is not
2274 closed by subsequent @code{getnetbyname} or @code{getnetbyaddr} calls,
2275 possibly giving an efficiency gain.
2278 @deffn {Scheme Procedure} getnetent
2279 Return the next entry from the network database.
2282 @deffn {Scheme Procedure} endnetent
2283 Close the stream used by @code{getnetent}. The return value is unspecified.
2286 @deffn {Scheme Procedure} setnet [stayopen]
2287 @deffnx {C Function} scm_setnet (stayopen)
2288 If @var{stayopen} is omitted, this is equivalent to @code{endnetent}.
2289 Otherwise it is equivalent to @code{setnetent stayopen}.
2292 @subsubheading The Protocol Database
2293 @cindex @file{/etc/protocols}
2295 @cindex network protocols
2297 The following functions accept an object representing a protocol
2298 and return a selected component:
2300 @deffn {Scheme Procedure} protoent:name protocol
2301 The ``official'' protocol name.
2303 @deffn {Scheme Procedure} protoent:aliases protocol
2304 A list of aliases for the protocol.
2306 @deffn {Scheme Procedure} protoent:proto protocol
2307 The protocol number.
2310 The following procedures are used to search the protocol database:
2312 @deffn {Scheme Procedure} getproto [protocol]
2313 @deffnx {Scheme Procedure} getprotobyname name
2314 @deffnx {Scheme Procedure} getprotobynumber number
2315 @deffnx {C Function} scm_getproto (protocol)
2316 Look up a network protocol by name or by number. @code{getprotobyname}
2317 takes a string argument, and @code{getprotobynumber} takes an integer
2318 argument. @code{getproto} will accept either type, behaving like
2319 @code{getprotoent} (see below) if no arguments are supplied.
2322 The following procedures may be used to step through the protocol
2323 database from beginning to end.
2325 @deffn {Scheme Procedure} setprotoent [stayopen]
2326 Initialize an internal stream from which protocol objects may be read. This
2327 procedure must be called before any calls to @code{getprotoent}, and may
2328 also be called afterward to reset the protocol entry stream. If
2329 @var{stayopen} is supplied and is not @code{#f}, the database is not
2330 closed by subsequent @code{getprotobyname} or @code{getprotobynumber} calls,
2331 possibly giving an efficiency gain.
2334 @deffn {Scheme Procedure} getprotoent
2335 Return the next entry from the protocol database.
2338 @deffn {Scheme Procedure} endprotoent
2339 Close the stream used by @code{getprotoent}. The return value is unspecified.
2342 @deffn {Scheme Procedure} setproto [stayopen]
2343 @deffnx {C Function} scm_setproto (stayopen)
2344 If @var{stayopen} is omitted, this is equivalent to @code{endprotoent}.
2345 Otherwise it is equivalent to @code{setprotoent stayopen}.
2348 @subsubheading The Service Database
2349 @cindex @file{/etc/services}
2351 @cindex network services
2353 The following functions accept an object representing a service
2354 and return a selected component:
2356 @deffn {Scheme Procedure} servent:name serv
2357 The ``official'' name of the network service.
2359 @deffn {Scheme Procedure} servent:aliases serv
2360 A list of aliases for the network service.
2362 @deffn {Scheme Procedure} servent:port serv
2363 The Internet port used by the service.
2365 @deffn {Scheme Procedure} servent:proto serv
2366 The protocol used by the service. A service may be listed many times
2367 in the database under different protocol names.
2370 The following procedures are used to search the service database:
2372 @deffn {Scheme Procedure} getserv [name [protocol]]
2373 @deffnx {Scheme Procedure} getservbyname name protocol
2374 @deffnx {Scheme Procedure} getservbyport port protocol
2375 @deffnx {C Function} scm_getserv (name, protocol)
2376 Look up a network service by name or by service number, and return a
2377 network service object. The @var{protocol} argument specifies the name
2378 of the desired protocol; if the protocol found in the network service
2379 database does not match this name, a system error is signalled.
2381 The @code{getserv} procedure will take either a service name or number
2382 as its first argument; if given no arguments, it behaves like
2383 @code{getservent} (see below).
2386 (getserv "imap" "tcp")
2387 @result{} #("imap2" ("imap") 143 "tcp")
2389 (getservbyport 88 "udp")
2390 @result{} #("kerberos" ("kerberos5" "krb5") 88 "udp")
2394 The following procedures may be used to step through the service
2395 database from beginning to end.
2397 @deffn {Scheme Procedure} setservent [stayopen]
2398 Initialize an internal stream from which service objects may be read. This
2399 procedure must be called before any calls to @code{getservent}, and may
2400 also be called afterward to reset the service entry stream. If
2401 @var{stayopen} is supplied and is not @code{#f}, the database is not
2402 closed by subsequent @code{getservbyname} or @code{getservbyport} calls,
2403 possibly giving an efficiency gain.
2406 @deffn {Scheme Procedure} getservent
2407 Return the next entry from the services database.
2410 @deffn {Scheme Procedure} endservent
2411 Close the stream used by @code{getservent}. The return value is unspecified.
2414 @deffn {Scheme Procedure} setserv [stayopen]
2415 @deffnx {C Function} scm_setserv (stayopen)
2416 If @var{stayopen} is omitted, this is equivalent to @code{endservent}.
2417 Otherwise it is equivalent to @code{setservent stayopen}.
2420 @node Network Sockets and Communication
2421 @subsubsection Network Sockets and Communication
2423 @cindex network socket
2425 Socket ports can be created using @code{socket} and @code{socketpair}.
2426 The ports are initially unbuffered, to make reading and writing to the
2427 same port more reliable. A buffer can be added to the port using
2428 @code{setvbuf}; see @ref{Ports and File Descriptors}.
2430 Most systems have limits on how many files and sockets can be open, so
2431 it's strongly recommended that socket ports be closed explicitly when
2432 no longer required (@pxref{Ports}).
2434 The convention used for ``host'' vs.@: ``network'' addresses is that
2435 addresses are always held in host order at the Scheme level. The
2436 procedures in this section automatically convert between host and
2437 network order when required. The arguments and return values are thus
2440 @deffn {Scheme Procedure} socket family style proto
2441 @deffnx {C Function} scm_socket (family, style, proto)
2442 Return a new socket port of the type specified by @var{family},
2443 @var{style} and @var{proto}. All three parameters are integers. The
2444 possible values for @var{family} are as follows, where supported by
2452 The possible values for @var{style} are as follows, again where
2453 supported by the system,
2459 @defvarx SOCK_SEQPACKET
2462 @var{proto} can be obtained from a protocol name using
2463 @code{getprotobyname} (@pxref{Network Databases}). A value of zero
2464 means the default protocol, which is usually right.
2466 A socket cannot by used for communication until it has been connected
2467 somewhere, usually with either @code{connect} or @code{accept} below.
2470 @deffn {Scheme Procedure} socketpair family style proto
2471 @deffnx {C Function} scm_socketpair (family, style, proto)
2472 Return a pair, the @code{car} and @code{cdr} of which are two unnamed
2473 socket ports connected to each other. The connection is full-duplex,
2474 so data can be transferred in either direction between the two.
2476 @var{family}, @var{style} and @var{proto} are as per @code{socket}
2477 above. But many systems only support socket pairs in the
2478 @code{PF_UNIX} family. Zero is likely to be the only meaningful value
2482 @deffn {Scheme Procedure} getsockopt sock level optname
2483 @deffnx {C Function} scm_getsockopt (sock, level, optname)
2484 Return the value of a particular socket option for the socket
2485 port @var{sock}. @var{level} is an integer code for type of
2486 option being requested, e.g., @code{SOL_SOCKET} for
2487 socket-level options. @var{optname} is an integer code for the
2488 option required and should be specified using one of the
2489 symbols @code{SO_DEBUG}, @code{SO_REUSEADDR} etc.
2491 The returned value is typically an integer but @code{SO_LINGER}
2492 returns a pair of integers.
2495 @deffn {Scheme Procedure} setsockopt sock level optname value
2496 @deffnx {C Function} scm_setsockopt (sock, level, optname, value)
2497 Set the value of a particular socket option for the socket
2498 port @var{sock}. @var{level} is an integer code for type of option
2499 being set, e.g., @code{SOL_SOCKET} for socket-level options.
2501 integer code for the option to set and should be specified using one of
2502 the symbols @code{SO_DEBUG}, @code{SO_REUSEADDR} etc.
2503 @var{value} is the value to which the option should be set. For
2504 most options this must be an integer, but for @code{SO_LINGER} it must
2507 The return value is unspecified.
2510 @deffn {Scheme Procedure} shutdown sock how
2511 @deffnx {C Function} scm_shutdown (sock, how)
2512 Sockets can be closed simply by using @code{close-port}. The
2513 @code{shutdown} procedure allows reception or transmission on a
2514 connection to be shut down individually, according to the parameter
2519 Stop receiving data for this socket. If further data arrives, reject it.
2521 Stop trying to transmit data from this socket. Discard any
2522 data waiting to be sent. Stop looking for acknowledgement of
2523 data already sent; don't retransmit it if it is lost.
2525 Stop both reception and transmission.
2528 The return value is unspecified.
2531 @deffn {Scheme Procedure} connect sock fam address . args
2532 @deffnx {C Function} scm_connect (sock, fam, address, args)
2533 Initiate a connection from a socket using a specified address
2534 family to the address
2535 specified by @var{address} and possibly @var{args}.
2536 The format required for @var{address}
2537 and @var{args} depends on the family of the socket.
2539 For a socket of family @code{AF_UNIX},
2540 only @var{address} is specified and must be a string with the
2541 filename where the socket is to be created.
2543 For a socket of family @code{AF_INET},
2544 @var{address} must be an integer IPv4 host address and
2545 @var{args} must be a single integer port number.
2547 For a socket of family @code{AF_INET6},
2548 @var{address} must be an integer IPv6 host address and
2549 @var{args} may be up to three integers:
2550 port [flowinfo] [scope_id],
2551 where flowinfo and scope_id default to zero.
2553 The return value is unspecified.
2556 @deffn {Scheme Procedure} bind sock fam address . args
2557 @deffnx {C Function} scm_bind (sock, fam, address, args)
2558 Assign an address to the socket port @var{sock}.
2559 Generally this only needs to be done for server sockets,
2560 so they know where to look for incoming connections. A socket
2561 without an address will be assigned one automatically when it
2562 starts communicating.
2564 The format of @var{address} and @var{args} depends
2565 on the family of the socket.
2567 For a socket of family @code{AF_UNIX}, only @var{address}
2568 is specified and must be a string with the filename where
2569 the socket is to be created.
2571 For a socket of family @code{AF_INET}, @var{address}
2572 must be an integer IPv4 address and @var{args}
2573 must be a single integer port number.
2575 The values of the following variables can also be used for
2579 Allow connections from any address.
2582 @defvar INADDR_LOOPBACK
2583 The address of the local host using the loopback device.
2586 @defvar INADDR_BROADCAST
2587 The broadcast address on the local network.
2594 For a socket of family @code{AF_INET6}, @var{address}
2595 must be an integer IPv6 address and @var{args}
2596 may be up to three integers:
2597 port [flowinfo] [scope_id],
2598 where flowinfo and scope_id default to zero.
2600 The return value is unspecified.
2603 @deffn {Scheme Procedure} listen sock backlog
2604 @deffnx {C Function} scm_listen (sock, backlog)
2605 Enable @var{sock} to accept connection
2606 requests. @var{backlog} is an integer specifying
2607 the maximum length of the queue for pending connections.
2608 If the queue fills, new clients will fail to connect until
2609 the server calls @code{accept} to accept a connection from
2612 The return value is unspecified.
2615 @deffn {Scheme Procedure} accept sock
2616 @deffnx {C Function} scm_accept (sock)
2617 Accept a connection on a bound, listening socket.
2619 are no pending connections in the queue, wait until
2620 one is available unless the non-blocking option has been
2623 The return value is a
2624 pair in which the @acronym{CAR} is a new socket port for the
2626 the @acronym{CDR} is an object with address information about the
2627 client which initiated the connection.
2629 @var{sock} does not become part of the
2630 connection and will continue to accept new requests.
2633 The following functions take a socket address object, as returned
2634 by @code{accept} and other procedures, and return a selected component.
2636 @deffn {Scheme Procedure} sockaddr:fam sa
2637 The socket family, typically equal to the value of @code{AF_UNIX} or
2640 @deffn {Scheme Procedure} sockaddr:path sa
2641 If the socket family is @code{AF_UNIX}, returns the path of the
2642 filename the socket is based on.
2644 @deffn {Scheme Procedure} sockaddr:addr sa
2645 If the socket family is @code{AF_INET}, returns the Internet host
2648 @deffn {Scheme Procedure} sockaddr:port sa
2649 If the socket family is @code{AF_INET}, returns the Internet port
2653 @deffn {Scheme Procedure} getsockname sock
2654 @deffnx {C Function} scm_getsockname (sock)
2655 Return the address of @var{sock}, in the same form as the
2656 object returned by @code{accept}. On many systems the address
2657 of a socket in the @code{AF_FILE} namespace cannot be read.
2660 @deffn {Scheme Procedure} getpeername sock
2661 @deffnx {C Function} scm_getpeername (sock)
2662 Return the address that @var{sock}
2663 is connected to, in the same form as the object returned by
2664 @code{accept}. On many systems the address of a socket in the
2665 @code{AF_FILE} namespace cannot be read.
2668 @deffn {Scheme Procedure} recv! sock buf [flags]
2669 @deffnx {C Function} scm_recv (sock, buf, flags)
2670 Receive data from a socket port.
2671 @var{sock} must already
2672 be bound to the address from which data is to be received.
2673 @var{buf} is a string into which
2674 the data will be written. The size of @var{buf} limits
2676 data which can be received: in the case of packet
2677 protocols, if a packet larger than this limit is encountered
2679 will be irrevocably lost.
2683 @vindex MSG_DONTROUTE
2684 The optional @var{flags} argument is a value or bitwise OR of
2685 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
2687 The value returned is the number of bytes read from the
2690 Note that the data is read directly from the socket file
2692 any unread buffered port data is ignored.
2695 @deffn {Scheme Procedure} send sock message [flags]
2696 @deffnx {C Function} scm_send (sock, message, flags)
2699 @vindex MSG_DONTROUTE
2700 Transmit the string @var{message} on a socket port @var{sock}.
2701 @var{sock} must already be bound to a destination address. The value
2702 returned is the number of bytes transmitted---it's possible for this
2703 to be less than the length of @var{message} if the socket is set to be
2704 non-blocking. The optional @var{flags} argument is a value or bitwise
2705 OR of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
2707 Note that the data is written directly to the socket
2709 any unflushed buffered port data is ignored.
2712 @deffn {Scheme Procedure} recvfrom! sock str [flags [start [end]]]
2713 @deffnx {C Function} scm_recvfrom (sock, str, flags, start, end)
2714 Return data from the socket port @var{sock} and also
2715 information about where the data was received from.
2716 @var{sock} must already be bound to the address from which
2717 data is to be received. @code{str}, is a string into which the
2718 data will be written. The size of @var{str} limits the amount
2719 of data which can be received: in the case of packet protocols,
2720 if a packet larger than this limit is encountered then some
2721 data will be irrevocably lost.
2725 @vindex MSG_DONTROUTE
2726 The optional @var{flags} argument is a value or bitwise OR of
2727 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
2729 The value returned is a pair: the @acronym{CAR} is the number of
2730 bytes read from the socket and the @acronym{CDR} an address object
2731 in the same form as returned by @code{accept}. The address
2732 will given as @code{#f} if not available, as is usually the
2733 case for stream sockets.
2735 The @var{start} and @var{end} arguments specify a substring of
2736 @var{str} to which the data should be written.
2738 Note that the data is read directly from the socket file
2739 descriptor: any unread buffered port data is ignored.
2742 @deffn {Scheme Procedure} sendto sock message fam address . args_and_flags
2743 @deffnx {C Function} scm_sendto (sock, message, fam, address, args_and_flags)
2744 Transmit the string @var{message} on the socket port
2746 destination address is specified using the @var{fam},
2748 @var{args_and_flags} arguments, in a similar way to the
2749 @code{connect} procedure. @var{args_and_flags} contains
2750 the usual connection arguments optionally followed by
2751 a flags argument, which is a value or
2752 bitwise OR of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
2754 The value returned is the number of bytes transmitted --
2756 this to be less than the length of @var{message} if the
2758 set to be non-blocking.
2759 Note that the data is written directly to the socket
2761 any unflushed buffered port data is ignored.
2764 The following functions can be used to convert short and long integers
2765 between ``host'' and ``network'' order. Although the procedures above do
2766 this automatically for addresses, the conversion will still need to
2767 be done when sending or receiving encoded integer data from the network.
2769 @deffn {Scheme Procedure} htons value
2770 @deffnx {C Function} scm_htons (value)
2771 Convert a 16 bit quantity from host to network byte ordering.
2772 @var{value} is packed into 2 bytes, which are then converted
2773 and returned as a new integer.
2776 @deffn {Scheme Procedure} ntohs value
2777 @deffnx {C Function} scm_ntohs (value)
2778 Convert a 16 bit quantity from network to host byte ordering.
2779 @var{value} is packed into 2 bytes, which are then converted
2780 and returned as a new integer.
2783 @deffn {Scheme Procedure} htonl value
2784 @deffnx {C Function} scm_htonl (value)
2785 Convert a 32 bit quantity from host to network byte ordering.
2786 @var{value} is packed into 4 bytes, which are then converted
2787 and returned as a new integer.
2790 @deffn {Scheme Procedure} ntohl value
2791 @deffnx {C Function} scm_ntohl (value)
2792 Convert a 32 bit quantity from network to host byte ordering.
2793 @var{value} is packed into 4 bytes, which are then converted
2794 and returned as a new integer.
2797 These procedures are inconvenient to use at present, but consider:
2800 (define write-network-long
2801 (lambda (value port)
2802 (let ((v (make-uniform-vector 1 1 0)))
2803 (uniform-vector-set! v 0 (htonl value))
2804 (uniform-vector-write v port))))
2806 (define read-network-long
2808 (let ((v (make-uniform-vector 1 1 0)))
2809 (uniform-vector-read! v port)
2810 (ntohl (uniform-vector-ref v 0)))))
2814 @node Internet Socket Examples
2815 @subsubsection Network Socket Examples
2816 @cindex network examples
2817 @cindex socket examples
2819 The following give examples of how to use network sockets.
2821 @subsubheading Internet Socket Client Example
2823 @cindex socket client example
2824 The following example demonstrates an Internet socket client.
2825 It connects to the HTTP daemon running on the local machine and
2826 returns the contents of the root index URL.
2829 (let ((s (socket PF_INET SOCK_STREAM 0)))
2830 (connect s AF_INET (inet-aton "127.0.0.1") 80)
2831 (display "GET / HTTP/1.0\r\n\r\n" s)
2833 (do ((line (read-line s) (read-line s)))
2834 ((eof-object? line))
2840 @subsubheading Internet Socket Server Example
2842 @cindex socket server example
2843 The following example shows a simple Internet server which listens on
2844 port 2904 for incoming connections and sends a greeting back to the
2848 (let ((s (socket PF_INET SOCK_STREAM 0)))
2849 (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
2850 ;; @r{Specific address?}
2851 ;; @r{(bind s AF_INET (inet-aton "127.0.0.1") 2904)}
2852 (bind s AF_INET INADDR_ANY 2904)
2855 (simple-format #t "Listening for clients in pid: ~S" (getpid))
2859 (let* ((client-connection (accept s))
2860 (client-details (cdr client-connection))
2861 (client (car client-connection)))
2862 (simple-format #t "Got new client connection: ~S"
2865 (simple-format #t "Client address: ~S"
2867 (sockaddr:addr client-details)))
2869 ;; @r{Send back the greeting to the client port}
2870 (display "Hello client\r\n" client)
2875 @node System Identification
2876 @subsection System Identification
2879 This section lists the various procedures Guile provides for accessing
2880 information about the system it runs on.
2882 @deffn {Scheme Procedure} uname
2883 @deffnx {C Function} scm_uname ()
2884 Return an object with some information about the computer
2885 system the program is running on.
2887 The following procedures accept an object as returned by @code{uname}
2888 and return a selected component.
2890 @deffn {Scheme Procedure} utsname:sysname un
2891 The name of the operating system.
2893 @deffn {Scheme Procedure} utsname:nodename un
2894 The network name of the computer.
2896 @deffn {Scheme Procedure} utsname:release un
2897 The current release level of the operating system implementation.
2899 @deffn {Scheme Procedure} utsname:version un
2900 The current version level within the release of the operating system.
2902 @deffn {Scheme Procedure} utsname:machine un
2903 A description of the hardware.
2907 @deffn {Scheme Procedure} gethostname
2908 @deffnx {C Function} scm_gethostname ()
2910 Return the host name of the current processor.
2913 @deffn {Scheme Procedure} sethostname name
2914 @deffnx {C Function} scm_sethostname (name)
2915 Set the host name of the current processor to @var{name}. May
2916 only be used by the superuser. The return value is not
2924 @deffn {Scheme Procedure} setlocale category [locale]
2925 @deffnx {C Function} scm_setlocale (category, locale)
2926 Get or set the current locale, used for various internationalizations.
2927 Locales are strings, such as @samp{sv_SE}.
2929 If @var{locale} is given then the locale for the given @var{category} is set
2930 and the new value returned. If @var{locale} is not given then the
2931 current value is returned. @var{category} should be one of the
2937 @defvarx LC_MESSAGES
2938 @defvarx LC_MONETARY
2944 A common usage is @samp{(setlocale LC_ALL "")}, which initializes all
2945 categories based on standard environment variables (@code{LANG} etc).
2946 For full details on categories and locale names @pxref{Locales,,
2947 Locales and Internationalization, libc, The GNU C Library Reference
2952 @subsection Encryption
2955 Please note that the procedures in this section are not suited for
2956 strong encryption, they are only interfaces to the well-known and
2957 common system library functions of the same name. They are just as good
2958 (or bad) as the underlying functions, so you should refer to your system
2959 documentation before using them.
2961 @deffn {Scheme Procedure} crypt key salt
2962 @deffnx {C Function} scm_crypt (key, salt)
2963 Encrypt @var{key} using @var{salt} as the salt value to the
2964 crypt(3) library call.
2967 Although @code{getpass} is not an encryption procedure per se, it
2968 appears here because it is often used in combination with @code{crypt}:
2970 @deffn {Scheme Procedure} getpass prompt
2971 @deffnx {C Function} scm_getpass (prompt)
2973 Display @var{prompt} to the standard error output and read
2974 a password from @file{/dev/tty}. If this file is not
2975 accessible, it reads from standard input. The password may be
2976 up to 127 characters in length. Additional characters and the
2977 terminating newline character are discarded. While reading
2978 the password, echoing and the generation of signals by special
2979 characters is disabled.
2984 @c TeX-master: "guile.texi"