2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010
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 port/fd cmd [value]
476 @deffnx {C Function} scm_fcntl (object, cmd, value)
477 Apply @var{cmd} on @var{port/fd}, either a port or file descriptor.
478 The @var{value} argument is used by the @code{SET} commands described
479 below, it's an integer value.
481 Values for @var{cmd} are:
484 Duplicate the file descriptor, the same as @code{dup->fdes} above
490 Get or set flags associated with the file descriptor. The only flag
494 ``Close on exec'', meaning the file descriptor will be closed on an
495 @code{exec} call (a successful such call). For example to set that
499 (fcntl port F_SETFD FD_CLOEXEC)
502 Or better, set it but leave any other possible future flags unchanged,
505 (fcntl port F_SETFD (logior FD_CLOEXEC
506 (fcntl port F_GETFD)))
513 Get or set flags associated with the open file. These flags are
514 @code{O_RDONLY} etc described under @code{open} above.
516 A common use is to set @code{O_NONBLOCK} on a network socket. The
517 following sets that flag, and leaves other flags unchanged.
520 (fcntl sock F_SETFL (logior O_NONBLOCK
521 (fcntl sock F_GETFL)))
527 Get or set the process ID of a socket's owner, for @code{SIGIO} signals.
531 @deffn {Scheme Procedure} flock file operation
532 @deffnx {C Function} scm_flock (file, operation)
534 Apply or remove an advisory lock on an open file.
535 @var{operation} specifies the action to be done:
538 Shared lock. More than one process may hold a shared lock
539 for a given file at a given time.
542 Exclusive lock. Only one process may hold an exclusive lock
543 for a given file at a given time.
549 Don't block when locking. This is combined with one of the other
550 operations using @code{logior} (@pxref{Bitwise Operations}). If
551 @code{flock} would block an @code{EWOULDBLOCK} error is thrown
552 (@pxref{Conventions}).
555 The return value is not specified. @var{file} may be an open
556 file descriptor or an open file descriptor port.
558 Note that @code{flock} does not lock files across NFS.
561 @deffn {Scheme Procedure} select reads writes excepts [secs [usecs]]
562 @deffnx {C Function} scm_select (reads, writes, excepts, secs, usecs)
563 This procedure has a variety of uses: waiting for the ability
564 to provide input, accept output, or the existence of
565 exceptional conditions on a collection of ports or file
566 descriptors, or waiting for a timeout to occur.
567 It also returns if interrupted by a signal.
569 @var{reads}, @var{writes} and @var{excepts} can be lists or
570 vectors, with each member a port or a file descriptor.
571 The value returned is a list of three corresponding
572 lists or vectors containing only the members which meet the
573 specified requirement. The ability of port buffers to
574 provide input or accept output is taken into account.
575 Ordering of the input lists or vectors is not preserved.
577 The optional arguments @var{secs} and @var{usecs} specify the
578 timeout. Either @var{secs} can be specified alone, as
579 either an integer or a real number, or both @var{secs} and
580 @var{usecs} can be specified as integers, in which case
581 @var{usecs} is an additional timeout expressed in
582 microseconds. If @var{secs} is omitted or is @code{#f} then
583 select will wait for as long as it takes for one of the other
584 conditions to be satisfied.
586 The scsh version of @code{select} differs as follows:
587 Only vectors are accepted for the first three arguments.
588 The @var{usecs} argument is not supported.
589 Multiple values are returned instead of a list.
590 Duplicates in the input vectors appear only once in output.
591 An additional @code{select!} interface is provided.
595 @subsection File System
598 These procedures allow querying and setting file system attributes
600 permissions, sizes and types of files); deleting, copying, renaming and
601 linking files; creating and removing directories and querying their
602 contents; syncing the file system and creating special files.
604 @deffn {Scheme Procedure} access? path how
605 @deffnx {C Function} scm_access (path, how)
606 Test accessibility of a file under the real UID and GID of the calling
607 process. The return is @code{#t} if @var{path} exists and the
608 permissions requested by @var{how} are all allowed, or @code{#f} if
611 @var{how} is an integer which is one of the following values, or a
612 bitwise-OR (@code{logior}) of multiple values.
615 Test for read permission.
618 Test for write permission.
621 Test for execute permission.
624 Test for existence of the file. This is implied by each of the other
625 tests, so there's no need to combine it with them.
628 It's important to note that @code{access?} does not simply indicate
629 what will happen on attempting to read or write a file. In normal
630 circumstances it does, but in a set-UID or set-GID program it doesn't
631 because @code{access?} tests the real ID, whereas an open or execute
632 attempt uses the effective ID.
634 A program which will never run set-UID/GID can ignore the difference
635 between real and effective IDs, but for maximum generality, especially
636 in library functions, it's best not to use @code{access?} to predict
637 the result of an open or execute, instead simply attempt that and
640 The main use for @code{access?} is to let a set-UID/GID program
641 determine what the invoking user would have been allowed to do,
642 without the greater (or perhaps lesser) privileges afforded by the
643 effective ID. For more on this, see @ref{Testing File Access,,, libc,
644 The GNU C Library Reference Manual}.
648 @deffn {Scheme Procedure} stat object
649 @deffnx {C Function} scm_stat (object)
650 Return an object containing various information about the file
651 determined by @var{obj}. @var{obj} can be a string containing
652 a file name or a port or integer file descriptor which is open
653 on a file (in which case @code{fstat} is used as the underlying
656 The object returned by @code{stat} can be passed as a single
657 parameter to the following procedures, all of which return
660 @deffn {Scheme Procedure} stat:dev st
661 The device number containing the file.
663 @deffn {Scheme Procedure} stat:ino st
664 The file serial number, which distinguishes this file from all
665 other files on the same device.
667 @deffn {Scheme Procedure} stat:mode st
668 The mode of the file. This is an integer which incorporates file type
669 information and file permission bits. See also @code{stat:type} and
670 @code{stat:perms} below.
672 @deffn {Scheme Procedure} stat:nlink st
673 The number of hard links to the file.
675 @deffn {Scheme Procedure} stat:uid st
676 The user ID of the file's owner.
678 @deffn {Scheme Procedure} stat:gid st
679 The group ID of the file.
681 @deffn {Scheme Procedure} stat:rdev st
682 Device ID; this entry is defined only for character or block special
683 files. On some systems this field is not available at all, in which
684 case @code{stat:rdev} returns @code{#f}.
686 @deffn {Scheme Procedure} stat:size st
687 The size of a regular file in bytes.
689 @deffn {Scheme Procedure} stat:atime st
690 The last access time for the file, in seconds.
692 @deffn {Scheme Procedure} stat:mtime st
693 The last modification time for the file, in seconds.
695 @deffn {Scheme Procedure} stat:ctime st
696 The last modification time for the attributes of the file, in seconds.
698 @deffn {Scheme Procedure} stat:atimensec st
699 @deffnx {Scheme Procedure} stat:mtimensec st
700 @deffnx {Scheme Procedure} stat:ctimensec st
701 The fractional part of a file's access, modification, or attribute modification
702 time, in nanoseconds. Nanosecond timestamps are only available on some operating
703 systems and file systems. If Guile cannot retrieve nanosecond-level timestamps
704 for a file, these fields will be set to 0.
706 @deffn {Scheme Procedure} stat:blksize st
707 The optimal block size for reading or writing the file, in bytes. On
708 some systems this field is not available, in which case
709 @code{stat:blksize} returns a sensible suggested block size.
711 @deffn {Scheme Procedure} stat:blocks st
712 The amount of disk space that the file occupies measured in units of
713 512 byte blocks. On some systems this field is not available, in
714 which case @code{stat:blocks} returns @code{#f}.
717 In addition, the following procedures return the information
718 from @code{stat:mode} in a more convenient form:
720 @deffn {Scheme Procedure} stat:type st
721 A symbol representing the type of file. Possible values are
722 @samp{regular}, @samp{directory}, @samp{symlink},
723 @samp{block-special}, @samp{char-special}, @samp{fifo}, @samp{socket},
726 @deffn {Scheme Procedure} stat:perms st
727 An integer representing the access permission bits.
731 @deffn {Scheme Procedure} lstat str
732 @deffnx {C Function} scm_lstat (str)
733 Similar to @code{stat}, but does not follow symbolic links, i.e.,
734 it will return information about a symbolic link itself, not the
735 file it points to. @var{path} must be a string.
738 @deffn {Scheme Procedure} readlink path
739 @deffnx {C Function} scm_readlink (path)
740 Return the value of the symbolic link named by @var{path} (a
741 string), i.e., the file that the link points to.
746 @deffn {Scheme Procedure} chown object owner group
747 @deffnx {C Function} scm_chown (object, owner, group)
748 Change the ownership and group of the file referred to by @var{object}
749 to the integer values @var{owner} and @var{group}. @var{object} can
750 be a string containing a file name or, if the platform supports
751 @code{fchown} (@pxref{File Owner,,,libc,The GNU C Library Reference
752 Manual}), a port or integer file descriptor which is open on the file.
753 The return value is unspecified.
755 If @var{object} is a symbolic link, either the
756 ownership of the link or the ownership of the referenced file will be
757 changed depending on the operating system (lchown is
758 unsupported at present). If @var{owner} or @var{group} is specified
759 as @code{-1}, then that ID is not changed.
763 @deffn {Scheme Procedure} chmod object mode
764 @deffnx {C Function} scm_chmod (object, mode)
765 Changes the permissions of the file referred to by @var{obj}.
766 @var{obj} can be a string containing a file name or a port or integer file
767 descriptor which is open on a file (in which case @code{fchmod} is used
768 as the underlying system call).
770 the new permissions as a decimal number, e.g., @code{(chmod "foo" #o755)}.
771 The return value is unspecified.
774 @deffn {Scheme Procedure} utime pathname [actime [modtime [actimens [modtimens [flags]]]]]
775 @deffnx {C Function} scm_utime (pathname, actime, modtime, actimens, modtimens, flags)
776 @code{utime} sets the access and modification times for the
777 file named by @var{path}. If @var{actime} or @var{modtime} is
778 not supplied, then the current time is used. @var{actime} and
779 @var{modtime} must be integer time values as returned by the
780 @code{current-time} procedure.
782 The optional @var{actimens} and @var{modtimens} are nanoseconds
783 to add @var{actime} and @var{modtime}. Nanosecond precision is
784 only supported on some combinations of file systems and operating
787 (utime "foo" (- (current-time) 3600))
789 will set the access time to one hour in the past and the
790 modification time to the current time.
794 @deffn {Scheme Procedure} delete-file str
795 @deffnx {C Function} scm_delete_file (str)
796 Deletes (or ``unlinks'') the file whose path is specified by
800 @deffn {Scheme Procedure} copy-file oldfile newfile
801 @deffnx {C Function} scm_copy_file (oldfile, newfile)
802 Copy the file specified by @var{oldfile} to @var{newfile}.
803 The return value is unspecified.
807 @deffn {Scheme Procedure} rename-file oldname newname
808 @deffnx {C Function} scm_rename (oldname, newname)
809 Renames the file specified by @var{oldname} to @var{newname}.
810 The return value is unspecified.
813 @deffn {Scheme Procedure} link oldpath newpath
814 @deffnx {C Function} scm_link (oldpath, newpath)
815 Creates a new name @var{newpath} in the file system for the
816 file named by @var{oldpath}. If @var{oldpath} is a symbolic
817 link, the link may or may not be followed depending on the
821 @deffn {Scheme Procedure} symlink oldpath newpath
822 @deffnx {C Function} scm_symlink (oldpath, newpath)
823 Create a symbolic link named @var{newpath} with the value (i.e., pointing to)
824 @var{oldpath}. The return value is unspecified.
827 @deffn {Scheme Procedure} mkdir path [mode]
828 @deffnx {C Function} scm_mkdir (path, mode)
829 Create a new directory named by @var{path}. If @var{mode} is omitted
830 then the permissions of the directory file are set using the current
831 umask (@pxref{Processes}). Otherwise they are set to the decimal
832 value specified with @var{mode}. The return value is unspecified.
835 @deffn {Scheme Procedure} rmdir path
836 @deffnx {C Function} scm_rmdir (path)
837 Remove the existing directory named by @var{path}. The directory must
838 be empty for this to succeed. The return value is unspecified.
841 @deffn {Scheme Procedure} opendir dirname
842 @deffnx {C Function} scm_opendir (dirname)
843 @cindex directory contents
844 Open the directory specified by @var{dirname} and return a directory
848 @deffn {Scheme Procedure} directory-stream? object
849 @deffnx {C Function} scm_directory_stream_p (object)
850 Return a boolean indicating whether @var{object} is a directory
851 stream as returned by @code{opendir}.
854 @deffn {Scheme Procedure} readdir stream
855 @deffnx {C Function} scm_readdir (stream)
856 Return (as a string) the next directory entry from the directory stream
857 @var{stream}. If there is no remaining entry to be read then the
858 end of file object is returned.
861 @deffn {Scheme Procedure} rewinddir stream
862 @deffnx {C Function} scm_rewinddir (stream)
863 Reset the directory port @var{stream} so that the next call to
864 @code{readdir} will return the first directory entry.
867 @deffn {Scheme Procedure} closedir stream
868 @deffnx {C Function} scm_closedir (stream)
869 Close the directory stream @var{stream}.
870 The return value is unspecified.
873 Here is an example showing how to display all the entries in a
877 (define dir (opendir "/usr/lib"))
878 (do ((entry (readdir dir) (readdir dir)))
879 ((eof-object? entry))
880 (display entry)(newline))
884 @deffn {Scheme Procedure} sync
885 @deffnx {C Function} scm_sync ()
886 Flush the operating system disk buffers.
887 The return value is unspecified.
890 @deffn {Scheme Procedure} mknod path type perms dev
891 @deffnx {C Function} scm_mknod (path, type, perms, dev)
893 Creates a new special file, such as a file corresponding to a device.
894 @var{path} specifies the name of the file. @var{type} should be one
895 of the following symbols: @samp{regular}, @samp{directory},
896 @samp{symlink}, @samp{block-special}, @samp{char-special},
897 @samp{fifo}, or @samp{socket}. @var{perms} (an integer) specifies the
898 file permissions. @var{dev} (an integer) specifies which device the
899 special file refers to. Its exact interpretation depends on the kind
900 of special file being created.
904 (mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))
907 The return value is unspecified.
910 @deffn {Scheme Procedure} tmpnam
911 @deffnx {C Function} scm_tmpnam ()
912 @cindex temporary file
913 Return an auto-generated name of a temporary file, a file which
914 doesn't already exist. The name includes a path, it's usually in
915 @file{/tmp} but that's system dependent.
917 Care must be taken when using @code{tmpnam}. In between choosing the
918 name and creating the file another program might use that name, or an
919 attacker might even make it a symlink pointing at something important
920 and causing you to overwrite that.
922 The safe way is to create the file using @code{open} with
923 @code{O_EXCL} to avoid any overwriting. A loop can try again with
924 another name if the file exists (error @code{EEXIST}).
925 @code{mkstemp!} below does that.
928 @deffn {Scheme Procedure} mkstemp! tmpl
929 @deffnx {C Function} scm_mkstemp (tmpl)
930 @cindex temporary file
931 Create a new unique file in the file system and return a new buffered
932 port open for reading and writing to the file.
934 @var{tmpl} is a string specifying where the file should be created: it
935 must end with @samp{XXXXXX} and those @samp{X}s will be changed in the
936 string to return the name of the file. (@code{port-filename} on the
937 port also gives the name.)
939 POSIX doesn't specify the permissions mode of the file, on GNU and
940 most systems it's @code{#o600}. An application can use @code{chmod}
941 to relax that if desired. For example @code{#o666} less @code{umask},
942 which is usual for ordinary file creation,
945 (let ((port (mkstemp! (string-copy "/tmp/myfile-XXXXXX"))))
946 (chmod port (logand #o666 (lognot (umask))))
951 @deffn {Scheme Procedure} dirname filename
952 @deffnx {C Function} scm_dirname (filename)
953 Return the directory name component of the file name
954 @var{filename}. If @var{filename} does not contain a directory
955 component, @code{.} is returned.
958 @deffn {Scheme Procedure} basename filename [suffix]
959 @deffnx {C Function} scm_basename (filename, suffix)
960 Return the base name of the file name @var{filename}. The
961 base name is the file name without any directory components.
962 If @var{suffix} is provided, and is equal to the end of
963 @var{basename}, it is removed also.
966 (basename "/tmp/test.xml" ".xml")
971 @deffn {Scheme Procedure} file-exists? filename
972 Return @code{#t} if the file named @var{filename} exists, @code{#f} if
977 @node User Information
978 @subsection User Information
979 @cindex user information
980 @cindex password file
983 The facilities in this section provide an interface to the user and
985 They should be used with care since they are not reentrant.
987 The following functions accept an object representing user information
988 and return a selected component:
990 @deffn {Scheme Procedure} passwd:name pw
991 The name of the userid.
993 @deffn {Scheme Procedure} passwd:passwd pw
994 The encrypted passwd.
996 @deffn {Scheme Procedure} passwd:uid pw
999 @deffn {Scheme Procedure} passwd:gid pw
1000 The group id number.
1002 @deffn {Scheme Procedure} passwd:gecos pw
1005 @deffn {Scheme Procedure} passwd:dir pw
1008 @deffn {Scheme Procedure} passwd:shell pw
1013 @deffn {Scheme Procedure} getpwuid uid
1014 Look up an integer userid in the user database.
1017 @deffn {Scheme Procedure} getpwnam name
1018 Look up a user name string in the user database.
1021 @deffn {Scheme Procedure} setpwent
1022 Initializes a stream used by @code{getpwent} to read from the user database.
1023 The next use of @code{getpwent} will return the first entry. The
1024 return value is unspecified.
1027 @deffn {Scheme Procedure} getpwent
1028 Read the next entry in the user database stream. The return is a
1029 passwd user object as above, or @code{#f} when no more entries.
1032 @deffn {Scheme Procedure} endpwent
1033 Closes the stream used by @code{getpwent}. The return value is unspecified.
1036 @deffn {Scheme Procedure} setpw [arg]
1037 @deffnx {C Function} scm_setpwent (arg)
1038 If called with a true argument, initialize or reset the password data
1039 stream. Otherwise, close the stream. The @code{setpwent} and
1040 @code{endpwent} procedures are implemented on top of this.
1043 @deffn {Scheme Procedure} getpw [user]
1044 @deffnx {C Function} scm_getpwuid (user)
1045 Look up an entry in the user database. @var{obj} can be an integer,
1046 a string, or omitted, giving the behaviour of getpwuid, getpwnam
1047 or getpwent respectively.
1050 The following functions accept an object representing group information
1051 and return a selected component:
1053 @deffn {Scheme Procedure} group:name gr
1056 @deffn {Scheme Procedure} group:passwd gr
1057 The encrypted group password.
1059 @deffn {Scheme Procedure} group:gid gr
1060 The group id number.
1062 @deffn {Scheme Procedure} group:mem gr
1063 A list of userids which have this group as a supplementary group.
1067 @deffn {Scheme Procedure} getgrgid gid
1068 Look up an integer group id in the group database.
1071 @deffn {Scheme Procedure} getgrnam name
1072 Look up a group name in the group database.
1075 @deffn {Scheme Procedure} setgrent
1076 Initializes a stream used by @code{getgrent} to read from the group database.
1077 The next use of @code{getgrent} will return the first entry.
1078 The return value is unspecified.
1081 @deffn {Scheme Procedure} getgrent
1082 Return the next entry in the group database, using the stream set by
1086 @deffn {Scheme Procedure} endgrent
1087 Closes the stream used by @code{getgrent}.
1088 The return value is unspecified.
1091 @deffn {Scheme Procedure} setgr [arg]
1092 @deffnx {C Function} scm_setgrent (arg)
1093 If called with a true argument, initialize or reset the group data
1094 stream. Otherwise, close the stream. The @code{setgrent} and
1095 @code{endgrent} procedures are implemented on top of this.
1098 @deffn {Scheme Procedure} getgr [name]
1099 @deffnx {C Function} scm_getgrgid (name)
1100 Look up an entry in the group database. @var{obj} can be an integer,
1101 a string, or omitted, giving the behaviour of getgrgid, getgrnam
1102 or getgrent respectively.
1105 In addition to the accessor procedures for the user database, the
1106 following shortcut procedures are also available.
1108 @deffn {Scheme Procedure} cuserid
1109 @deffnx {C Function} scm_cuserid ()
1110 Return a string containing a user name associated with the
1111 effective user id of the process. Return @code{#f} if this
1112 information cannot be obtained.
1114 This function has been removed from the latest POSIX specification,
1115 Guile provides it only if the system has it. Using @code{(getpwuid
1116 (geteuid))} may be a better idea.
1119 @deffn {Scheme Procedure} getlogin
1120 @deffnx {C Function} scm_getlogin ()
1121 Return a string containing the name of the user logged in on
1122 the controlling terminal of the process, or @code{#f} if this
1123 information cannot be obtained.
1131 @deffn {Scheme Procedure} current-time
1132 @deffnx {C Function} scm_current_time ()
1133 Return the number of seconds since 1970-01-01 00:00:00 @acronym{UTC},
1134 excluding leap seconds.
1137 @deffn {Scheme Procedure} gettimeofday
1138 @deffnx {C Function} scm_gettimeofday ()
1139 Return a pair containing the number of seconds and microseconds
1140 since 1970-01-01 00:00:00 @acronym{UTC}, excluding leap seconds. Note:
1141 whether true microsecond resolution is available depends on the
1145 The following procedures either accept an object representing a broken down
1146 time and return a selected component, or accept an object representing
1147 a broken down time and a value and set the component to the value.
1148 The numbers in parentheses give the usual range.
1150 @deffn {Scheme Procedure} tm:sec tm
1151 @deffnx {Scheme Procedure} set-tm:sec tm val
1154 @deffn {Scheme Procedure} tm:min tm
1155 @deffnx {Scheme Procedure} set-tm:min tm val
1158 @deffn {Scheme Procedure} tm:hour tm
1159 @deffnx {Scheme Procedure} set-tm:hour tm val
1162 @deffn {Scheme Procedure} tm:mday tm
1163 @deffnx {Scheme Procedure} set-tm:mday tm val
1164 Day of the month (1-31).
1166 @deffn {Scheme Procedure} tm:mon tm
1167 @deffnx {Scheme Procedure} set-tm:mon tm val
1170 @deffn {Scheme Procedure} tm:year tm
1171 @deffnx {Scheme Procedure} set-tm:year tm val
1172 Year (70-), the year minus 1900.
1174 @deffn {Scheme Procedure} tm:wday tm
1175 @deffnx {Scheme Procedure} set-tm:wday tm val
1176 Day of the week (0-6) with Sunday represented as 0.
1178 @deffn {Scheme Procedure} tm:yday tm
1179 @deffnx {Scheme Procedure} set-tm:yday tm val
1180 Day of the year (0-364, 365 in leap years).
1182 @deffn {Scheme Procedure} tm:isdst tm
1183 @deffnx {Scheme Procedure} set-tm:isdst tm val
1184 Daylight saving indicator (0 for ``no'', greater than 0 for ``yes'', less than
1187 @deffn {Scheme Procedure} tm:gmtoff tm
1188 @deffnx {Scheme Procedure} set-tm:gmtoff tm val
1189 Time zone offset in seconds west of @acronym{UTC} (-46800 to 43200).
1190 For example on East coast USA (zone @samp{EST+5}) this would be 18000
1191 (ie.@: @m{5\times60\times60,5*60*60}) in winter, or 14400
1192 (ie.@: @m{4\times60\times60,4*60*60}) during daylight savings.
1194 Note @code{tm:gmtoff} is not the same as @code{tm_gmtoff} in the C
1195 @code{tm} structure. @code{tm_gmtoff} is seconds east and hence the
1196 negative of the value here.
1198 @deffn {Scheme Procedure} tm:zone tm
1199 @deffnx {Scheme Procedure} set-tm:zone tm val
1200 Time zone label (a string), not necessarily unique.
1204 @deffn {Scheme Procedure} localtime time [zone]
1205 @deffnx {C Function} scm_localtime (time, zone)
1207 Return an object representing the broken down components of
1208 @var{time}, an integer like the one returned by
1209 @code{current-time}. The time zone for the calculation is
1210 optionally specified by @var{zone} (a string), otherwise the
1211 @env{TZ} environment variable or the system default is used.
1214 @deffn {Scheme Procedure} gmtime time
1215 @deffnx {C Function} scm_gmtime (time)
1216 Return an object representing the broken down components of
1217 @var{time}, an integer like the one returned by
1218 @code{current-time}. The values are calculated for @acronym{UTC}.
1221 @deffn {Scheme Procedure} mktime sbd-time [zone]
1222 @deffnx {C Function} scm_mktime (sbd_time, zone)
1223 For a broken down time object @var{sbd-time}, return a pair the
1224 @code{car} of which is an integer time like @code{current-time}, and
1225 the @code{cdr} of which is a new broken down time with normalized
1228 @var{zone} is a timezone string, or the default is the @env{TZ}
1229 environment variable or the system default (@pxref{TZ Variable,,
1230 Specifying the Time Zone with @env{TZ}, libc, GNU C Library Reference
1231 Manual}). @var{sbd-time} is taken to be in that @var{zone}.
1233 The following fields of @var{sbd-time} are used: @code{tm:year},
1234 @code{tm:mon}, @code{tm:mday}, @code{tm:hour}, @code{tm:min},
1235 @code{tm:sec}, @code{tm:isdst}. The values can be outside their usual
1236 ranges. For example @code{tm:hour} normally goes up to 23, but a
1237 value say 33 would mean 9 the following day.
1239 @code{tm:isdst} in @var{sbd-time} says whether the time given is with
1240 daylight savings or not. This is ignored if @var{zone} doesn't have
1241 any daylight savings adjustment amount.
1243 The broken down time in the return normalizes the values of
1244 @var{sbd-time} by bringing them into their usual ranges, and using the
1245 actual daylight savings rule for that time in @var{zone} (which may
1246 differ from what @var{sbd-time} had). The easiest way to think of
1247 this is that @var{sbd-time} plus @var{zone} converts to the integer
1248 UTC time, then a @code{localtime} is applied to get the normal
1249 presentation of that time, in @var{zone}.
1252 @deffn {Scheme Procedure} tzset
1253 @deffnx {C Function} scm_tzset ()
1254 Initialize the timezone from the @env{TZ} environment variable
1255 or the system default. It's not usually necessary to call this procedure
1256 since it's done automatically by other procedures that depend on the
1260 @deffn {Scheme Procedure} strftime format tm
1261 @deffnx {C Function} scm_strftime (format, tm)
1262 @cindex time formatting
1263 Return a string which is broken-down time structure @var{tm} formatted
1264 according to the given @var{format} string.
1266 @var{format} contains field specifications introduced by a @samp{%}
1267 character. See @ref{Formatting Calendar Time,,, libc, The GNU C
1268 Library Reference Manual}, or @samp{man 3 strftime}, for the available
1272 (strftime "%c" (localtime (current-time)))
1273 @result{} "Mon Mar 11 20:17:43 2002"
1276 If @code{setlocale} has been called (@pxref{Locales}), month and day
1277 names are from the current locale and in the locale character set.
1280 @deffn {Scheme Procedure} strptime format string
1281 @deffnx {C Function} scm_strptime (format, string)
1282 @cindex time parsing
1283 Performs the reverse action to @code{strftime}, parsing
1284 @var{string} according to the specification supplied in
1285 @var{template}. The interpretation of month and day names is
1286 dependent on the current locale. The value returned is a pair.
1287 The @acronym{CAR} has an object with time components
1288 in the form returned by @code{localtime} or @code{gmtime},
1289 but the time zone components
1290 are not usefully set.
1291 The @acronym{CDR} reports the number of characters from @var{string}
1292 which were used for the conversion.
1295 @defvar internal-time-units-per-second
1296 The value of this variable is the number of time units per second
1297 reported by the following procedures.
1300 @deffn {Scheme Procedure} times
1301 @deffnx {C Function} scm_times ()
1302 Return an object with information about real and processor
1303 time. The following procedures accept such an object as an
1304 argument and return a selected component:
1306 @deffn {Scheme Procedure} tms:clock tms
1307 The current real time, expressed as time units relative to an
1310 @deffn {Scheme Procedure} tms:utime tms
1311 The CPU time units used by the calling process.
1313 @deffn {Scheme Procedure} tms:stime tms
1314 The CPU time units used by the system on behalf of the calling
1317 @deffn {Scheme Procedure} tms:cutime tms
1318 The CPU time units used by terminated child processes of the
1319 calling process, whose status has been collected (e.g., using
1322 @deffn {Scheme Procedure} tms:cstime tms
1323 Similarly, the CPU times units used by the system on behalf of
1324 terminated child processes.
1328 @deffn {Scheme Procedure} get-internal-real-time
1329 @deffnx {C Function} scm_get_internal_real_time ()
1330 Return the number of time units since the interpreter was
1334 @deffn {Scheme Procedure} get-internal-run-time
1335 @deffnx {C Function} scm_get_internal_run_time ()
1336 Return the number of time units of processor time used by the
1337 interpreter. Both @emph{system} and @emph{user} time are
1338 included but subprocesses are not.
1341 @node Runtime Environment
1342 @subsection Runtime Environment
1344 @deffn {Scheme Procedure} program-arguments
1345 @deffnx {Scheme Procedure} command-line
1346 @deffnx {Scheme Procedure} set-program-arguments
1347 @deffnx {C Function} scm_program_arguments ()
1348 @deffnx {C Function} scm_set_program_arguments_scm (lst)
1349 @cindex command line
1350 @cindex program arguments
1351 Get the command line arguments passed to Guile, or set new arguments.
1353 The arguments are a list of strings, the first of which is the invoked
1354 program name. This is just @nicode{"guile"} (or the executable path)
1355 when run interactively, or it's the script name when running a script
1356 with @option{-s} (@pxref{Invoking Guile}).
1359 guile -L /my/extra/dir -s foo.scm abc def
1361 (program-arguments) @result{} ("foo.scm" "abc" "def")
1364 @code{set-program-arguments} allows a library module or similar to
1365 modify the arguments, for example to strip options it recognises,
1366 leaving the rest for the mainline.
1368 The argument list is held in a fluid, which means it's separate for
1369 each thread. Neither the list nor the strings within it are copied at
1370 any point and normally should not be mutated.
1372 The two names @code{program-arguments} and @code{command-line} are an
1373 historical accident, they both do exactly the same thing. The name
1374 @code{scm_set_program_arguments_scm} has an extra @code{_scm} on the
1375 end to avoid clashing with the C function below.
1378 @deftypefn {C Function} void scm_set_program_arguments (int argc, char **argv, char *first)
1379 @cindex command line
1380 @cindex program arguments
1381 Set the list of command line arguments for @code{program-arguments}
1382 and @code{command-line} above.
1384 @var{argv} is an array of null-terminated strings, as in a C
1385 @code{main} function. @var{argc} is the number of strings in
1386 @var{argv}, or if it's negative then a @code{NULL} in @var{argv} marks
1389 @var{first} is an extra string put at the start of the arguments, or
1390 @code{NULL} for no such extra. This is a convenient way to pass the
1391 program name after advancing @var{argv} to strip option arguments.
1396 char *progname = argv[0];
1397 for (argv++; argv[0] != NULL && argv[0][0] == '-'; argv++)
1399 /* munch option ... */
1401 /* remaining args for scheme level use */
1402 scm_set_program_arguments (-1, argv, progname);
1406 This sort of thing is often done at startup under
1407 @code{scm_boot_guile} with options handled at the C level removed.
1408 The given strings are all copied, so the C data is not accessed again
1409 once @code{scm_set_program_arguments} returns.
1412 @deffn {Scheme Procedure} getenv nam
1413 @deffnx {C Function} scm_getenv (nam)
1415 Looks up the string @var{name} in the current environment. The return
1416 value is @code{#f} unless a string of the form @code{NAME=VALUE} is
1417 found, in which case the string @code{VALUE} is returned.
1420 @deffn {Scheme Procedure} setenv name value
1421 Modifies the environment of the current process, which is
1422 also the default environment inherited by child processes.
1424 If @var{value} is @code{#f}, then @var{name} is removed from the
1425 environment. Otherwise, the string @var{name}=@var{value} is added
1426 to the environment, replacing any existing string with name matching
1429 The return value is unspecified.
1432 @deffn {Scheme Procedure} unsetenv name
1433 Remove variable @var{name} from the environment. The
1434 name can not contain a @samp{=} character.
1437 @deffn {Scheme Procedure} environ [env]
1438 @deffnx {C Function} scm_environ (env)
1439 If @var{env} is omitted, return the current environment (in the
1440 Unix sense) as a list of strings. Otherwise set the current
1441 environment, which is also the default environment for child
1442 processes, to the supplied list of strings. Each member of
1443 @var{env} should be of the form @var{NAME}=@var{VALUE} and values of
1444 @var{NAME} should not be duplicated. If @var{env} is supplied
1445 then the return value is unspecified.
1448 @deffn {Scheme Procedure} putenv str
1449 @deffnx {C Function} scm_putenv (str)
1450 Modifies the environment of the current process, which is
1451 also the default environment inherited by child processes.
1453 If @var{string} is of the form @code{NAME=VALUE} then it will be written
1454 directly into the environment, replacing any existing environment string
1456 name matching @code{NAME}. If @var{string} does not contain an equal
1457 sign, then any existing string with name matching @var{string} will
1460 The return value is unspecified.
1465 @subsection Processes
1467 @cindex child processes
1470 @deffn {Scheme Procedure} chdir str
1471 @deffnx {C Function} scm_chdir (str)
1472 @cindex current directory
1473 Change the current working directory to @var{path}.
1474 The return value is unspecified.
1478 @deffn {Scheme Procedure} getcwd
1479 @deffnx {C Function} scm_getcwd ()
1480 Return the name of the current working directory.
1483 @deffn {Scheme Procedure} umask [mode]
1484 @deffnx {C Function} scm_umask (mode)
1485 If @var{mode} is omitted, returns a decimal number representing the
1486 current file creation mask. Otherwise the file creation mask is set
1487 to @var{mode} and the previous value is returned. @xref{Setting
1488 Permissions,,Assigning File Permissions,libc,The GNU C Library
1489 Reference Manual}, for more on how to use umasks.
1491 E.g., @code{(umask #o022)} sets the mask to octal 22/decimal 18.
1494 @deffn {Scheme Procedure} chroot path
1495 @deffnx {C Function} scm_chroot (path)
1496 Change the root directory to that specified in @var{path}.
1497 This directory will be used for path names beginning with
1498 @file{/}. The root directory is inherited by all children
1499 of the current process. Only the superuser may change the
1503 @deffn {Scheme Procedure} getpid
1504 @deffnx {C Function} scm_getpid ()
1505 Return an integer representing the current process ID.
1508 @deffn {Scheme Procedure} getgroups
1509 @deffnx {C Function} scm_getgroups ()
1510 Return a vector of integers representing the current
1511 supplementary group IDs.
1514 @deffn {Scheme Procedure} getppid
1515 @deffnx {C Function} scm_getppid ()
1516 Return an integer representing the process ID of the parent
1520 @deffn {Scheme Procedure} getuid
1521 @deffnx {C Function} scm_getuid ()
1522 Return an integer representing the current real user ID.
1525 @deffn {Scheme Procedure} getgid
1526 @deffnx {C Function} scm_getgid ()
1527 Return an integer representing the current real group ID.
1530 @deffn {Scheme Procedure} geteuid
1531 @deffnx {C Function} scm_geteuid ()
1532 Return an integer representing the current effective user ID.
1533 If the system does not support effective IDs, then the real ID
1534 is returned. @code{(provided? 'EIDs)} reports whether the
1535 system supports effective IDs.
1538 @deffn {Scheme Procedure} getegid
1539 @deffnx {C Function} scm_getegid ()
1540 Return an integer representing the current effective group ID.
1541 If the system does not support effective IDs, then the real ID
1542 is returned. @code{(provided? 'EIDs)} reports whether the
1543 system supports effective IDs.
1546 @deffn {Scheme Procedure} setgroups vec
1547 @deffnx {C Function} scm_setgroups (vec)
1548 Set the current set of supplementary group IDs to the integers in the
1549 given vector @var{vec}. The return value is unspecified.
1551 Generally only the superuser can set the process group IDs
1552 (@pxref{Setting Groups, Setting the Group IDs,, libc, The GNU C
1553 Library Reference Manual}).
1556 @deffn {Scheme Procedure} setuid id
1557 @deffnx {C Function} scm_setuid (id)
1558 Sets both the real and effective user IDs to the integer @var{id}, provided
1559 the process has appropriate privileges.
1560 The return value is unspecified.
1563 @deffn {Scheme Procedure} setgid id
1564 @deffnx {C Function} scm_setgid (id)
1565 Sets both the real and effective group IDs to the integer @var{id}, provided
1566 the process has appropriate privileges.
1567 The return value is unspecified.
1570 @deffn {Scheme Procedure} seteuid id
1571 @deffnx {C Function} scm_seteuid (id)
1572 Sets the effective user ID to the integer @var{id}, provided the process
1573 has appropriate privileges. If effective IDs are not supported, the
1574 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1575 system supports effective IDs.
1576 The return value is unspecified.
1579 @deffn {Scheme Procedure} setegid id
1580 @deffnx {C Function} scm_setegid (id)
1581 Sets the effective group ID to the integer @var{id}, provided the process
1582 has appropriate privileges. If effective IDs are not supported, the
1583 real ID is set instead---@code{(provided? 'EIDs)} reports whether the
1584 system supports effective IDs.
1585 The return value is unspecified.
1588 @deffn {Scheme Procedure} getpgrp
1589 @deffnx {C Function} scm_getpgrp ()
1590 Return an integer representing the current process group ID.
1591 This is the @acronym{POSIX} definition, not @acronym{BSD}.
1594 @deffn {Scheme Procedure} setpgid pid pgid
1595 @deffnx {C Function} scm_setpgid (pid, pgid)
1596 Move the process @var{pid} into the process group @var{pgid}. @var{pid} or
1597 @var{pgid} must be integers: they can be zero to indicate the ID of the
1599 Fails on systems that do not support job control.
1600 The return value is unspecified.
1603 @deffn {Scheme Procedure} setsid
1604 @deffnx {C Function} scm_setsid ()
1605 Creates a new session. The current process becomes the session leader
1606 and is put in a new process group. The process will be detached
1607 from its controlling terminal if it has one.
1608 The return value is an integer representing the new process group ID.
1611 @deffn {Scheme Procedure} getsid pid
1612 @deffnx {C Function} scm_getsid (pid)
1613 Returns the session ID of process @var{pid}. (The session
1614 ID of a process is the process group ID of its session leader.)
1617 @deffn {Scheme Procedure} waitpid pid [options]
1618 @deffnx {C Function} scm_waitpid (pid, options)
1619 This procedure collects status information from a child process which
1620 has terminated or (optionally) stopped. Normally it will
1621 suspend the calling process until this can be done. If more than one
1622 child process is eligible then one will be chosen by the operating system.
1624 The value of @var{pid} determines the behaviour:
1627 @item @var{pid} greater than 0
1628 Request status information from the specified child process.
1629 @item @var{pid} equal to -1 or @code{WAIT_ANY}
1631 Request status information for any child process.
1632 @item @var{pid} equal to 0 or @code{WAIT_MYPGRP}
1634 Request status information for any child process in the current process
1636 @item @var{pid} less than -1
1637 Request status information for any child process whose process group ID
1638 is @minus{}@var{pid}.
1641 The @var{options} argument, if supplied, should be the bitwise OR of the
1642 values of zero or more of the following variables:
1645 Return immediately even if there are no child processes to be collected.
1649 Report status information for stopped processes as well as terminated
1653 The return value is a pair containing:
1657 The process ID of the child process, or 0 if @code{WNOHANG} was
1658 specified and no process was collected.
1660 The integer status value.
1665 functions can be used to decode the process status code returned
1668 @deffn {Scheme Procedure} status:exit-val status
1669 @deffnx {C Function} scm_status_exit_val (status)
1670 Return the exit status value, as would be set if a process
1671 ended normally through a call to @code{exit} or @code{_exit},
1672 if any, otherwise @code{#f}.
1675 @deffn {Scheme Procedure} status:term-sig status
1676 @deffnx {C Function} scm_status_term_sig (status)
1677 Return the signal number which terminated the process, if any,
1678 otherwise @code{#f}.
1681 @deffn {Scheme Procedure} status:stop-sig status
1682 @deffnx {C Function} scm_status_stop_sig (status)
1683 Return the signal number which stopped the process, if any,
1684 otherwise @code{#f}.
1687 @deffn {Scheme Procedure} system [cmd]
1688 @deffnx {C Function} scm_system (cmd)
1689 Execute @var{cmd} using the operating system's ``command
1690 processor''. Under Unix this is usually the default shell
1691 @code{sh}. The value returned is @var{cmd}'s exit status as
1692 returned by @code{waitpid}, which can be interpreted using the
1695 If @code{system} is called without arguments, return a boolean
1696 indicating whether the command processor is available.
1699 @deffn {Scheme Procedure} system* . args
1700 @deffnx {C Function} scm_system_star (args)
1701 Execute the command indicated by @var{args}. The first element must
1702 be a string indicating the command to be executed, and the remaining
1703 items must be strings representing each of the arguments to that
1706 This function returns the exit status of the command as provided by
1707 @code{waitpid}. This value can be handled with @code{status:exit-val}
1708 and the related functions.
1710 @code{system*} is similar to @code{system}, but accepts only one
1711 string per-argument, and performs no shell interpretation. The
1712 command is executed using fork and execlp. Accordingly this function
1713 may be safer than @code{system} in situations where shell
1714 interpretation is not required.
1716 Example: (system* "echo" "foo" "bar")
1719 @deffn {Scheme Procedure} primitive-exit [status]
1720 @deffnx {Scheme Procedure} primitive-_exit [status]
1721 @deffnx {C Function} scm_primitive_exit (status)
1722 @deffnx {C Function} scm_primitive__exit (status)
1723 Terminate the current process without unwinding the Scheme stack. The
1724 exit status is @var{status} if supplied, otherwise zero.
1726 @code{primitive-exit} uses the C @code{exit} function and hence runs
1727 usual C level cleanups (flush output streams, call @code{atexit}
1728 functions, etc, see @ref{Normal Termination,,, libc, The GNU C Library
1729 Reference Manual})).
1731 @code{primitive-_exit} is the @code{_exit} system call
1732 (@pxref{Termination Internals,,, libc, The GNU C Library Reference
1733 Manual}). This terminates the program immediately, with neither
1734 Scheme-level nor C-level cleanups.
1736 The typical use for @code{primitive-_exit} is from a child process
1737 created with @code{primitive-fork}. For example in a Gdk program the
1738 child process inherits the X server connection and a C-level
1739 @code{atexit} cleanup which will close that connection. But closing
1740 in the child would upset the protocol in the parent, so
1741 @code{primitive-_exit} should be used to exit without that.
1744 @deffn {Scheme Procedure} execl filename . args
1745 @deffnx {C Function} scm_execl (filename, args)
1746 Executes the file named by @var{path} as a new process image.
1747 The remaining arguments are supplied to the process; from a C program
1748 they are accessible as the @code{argv} argument to @code{main}.
1749 Conventionally the first @var{arg} is the same as @var{path}.
1750 All arguments must be strings.
1752 If @var{arg} is missing, @var{path} is executed with a null
1753 argument list, which may have system-dependent side-effects.
1755 This procedure is currently implemented using the @code{execv} system
1756 call, but we call it @code{execl} because of its Scheme calling interface.
1759 @deffn {Scheme Procedure} execlp filename . args
1760 @deffnx {C Function} scm_execlp (filename, args)
1761 Similar to @code{execl}, however if
1762 @var{filename} does not contain a slash
1763 then the file to execute will be located by searching the
1764 directories listed in the @code{PATH} environment variable.
1766 This procedure is currently implemented using the @code{execvp} system
1767 call, but we call it @code{execlp} because of its Scheme calling interface.
1770 @deffn {Scheme Procedure} execle filename env . args
1771 @deffnx {C Function} scm_execle (filename, env, args)
1772 Similar to @code{execl}, but the environment of the new process is
1773 specified by @var{env}, which must be a list of strings as returned by the
1774 @code{environ} procedure.
1776 This procedure is currently implemented using the @code{execve} system
1777 call, but we call it @code{execle} because of its Scheme calling interface.
1780 @deffn {Scheme Procedure} primitive-fork
1781 @deffnx {C Function} scm_fork ()
1782 Creates a new ``child'' process by duplicating the current ``parent'' process.
1783 In the child the return value is 0. In the parent the return value is
1784 the integer process ID of the child.
1786 This procedure has been renamed from @code{fork} to avoid a naming conflict
1790 @deffn {Scheme Procedure} nice incr
1791 @deffnx {C Function} scm_nice (incr)
1792 @cindex process priority
1793 Increment the priority of the current process by @var{incr}. A higher
1794 priority value means that the process runs less often.
1795 The return value is unspecified.
1798 @deffn {Scheme Procedure} setpriority which who prio
1799 @deffnx {C Function} scm_setpriority (which, who, prio)
1800 @vindex PRIO_PROCESS
1803 Set the scheduling priority of the process, process group
1804 or user, as indicated by @var{which} and @var{who}. @var{which}
1805 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1806 or @code{PRIO_USER}, and @var{who} is interpreted relative to
1807 @var{which} (a process identifier for @code{PRIO_PROCESS},
1808 process group identifier for @code{PRIO_PGRP}, and a user
1809 identifier for @code{PRIO_USER}. A zero value of @var{who}
1810 denotes the current process, process group, or user.
1811 @var{prio} is a value in the range [@minus{}20,20]. The default
1812 priority is 0; lower priorities (in numerical terms) cause more
1813 favorable scheduling. Sets the priority of all of the specified
1814 processes. Only the super-user may lower priorities. The return
1815 value is not specified.
1818 @deffn {Scheme Procedure} getpriority which who
1819 @deffnx {C Function} scm_getpriority (which, who)
1820 @vindex PRIO_PROCESS
1823 Return the scheduling priority of the process, process group
1824 or user, as indicated by @var{which} and @var{who}. @var{which}
1825 is one of the variables @code{PRIO_PROCESS}, @code{PRIO_PGRP}
1826 or @code{PRIO_USER}, and @var{who} should be interpreted depending on
1827 @var{which} (a process identifier for @code{PRIO_PROCESS},
1828 process group identifier for @code{PRIO_PGRP}, and a user
1829 identifier for @code{PRIO_USER}). A zero value of @var{who}
1830 denotes the current process, process group, or user. Return
1831 the highest priority (lowest numerical value) of any of the
1832 specified processes.
1840 The following procedures raise, handle and wait for signals.
1842 Scheme code signal handlers are run via a system async (@pxref{System
1843 asyncs}), so they're called in the handler's thread at the next safe
1844 opportunity. Generally this is after any currently executing
1845 primitive procedure finishes (which could be a long time for
1846 primitives that wait for an external event).
1848 @deffn {Scheme Procedure} kill pid sig
1849 @deffnx {C Function} scm_kill (pid, sig)
1850 Sends a signal to the specified process or group of processes.
1852 @var{pid} specifies the processes to which the signal is sent:
1855 @item @var{pid} greater than 0
1856 The process whose identifier is @var{pid}.
1857 @item @var{pid} equal to 0
1858 All processes in the current process group.
1859 @item @var{pid} less than -1
1860 The process group whose identifier is -@var{pid}
1861 @item @var{pid} equal to -1
1862 If the process is privileged, all processes except for some special
1863 system processes. Otherwise, all processes with the current effective
1867 @var{sig} should be specified using a variable corresponding to
1868 the Unix symbolic name, e.g.,
1878 A full list of signals on the GNU system may be found in @ref{Standard
1879 Signals,,,libc,The GNU C Library Reference Manual}.
1882 @deffn {Scheme Procedure} raise sig
1883 @deffnx {C Function} scm_raise (sig)
1884 Sends a specified signal @var{sig} to the current process, where
1885 @var{sig} is as described for the @code{kill} procedure.
1888 @deffn {Scheme Procedure} sigaction signum [handler [flags [thread]]]
1889 @deffnx {C Function} scm_sigaction (signum, handler, flags)
1890 @deffnx {C Function} scm_sigaction_for_thread (signum, handler, flags, thread)
1891 Install or report the signal handler for a specified signal.
1893 @var{signum} is the signal number, which can be specified using the value
1894 of variables such as @code{SIGINT}.
1896 If @var{handler} is omitted, @code{sigaction} returns a pair: the
1897 @acronym{CAR} is the current signal hander, which will be either an
1898 integer with the value @code{SIG_DFL} (default action) or
1899 @code{SIG_IGN} (ignore), or the Scheme procedure which handles the
1900 signal, or @code{#f} if a non-Scheme procedure handles the signal.
1901 The @acronym{CDR} contains the current @code{sigaction} flags for the
1904 If @var{handler} is provided, it is installed as the new handler for
1905 @var{signum}. @var{handler} can be a Scheme procedure taking one
1906 argument, or the value of @code{SIG_DFL} (default action) or
1907 @code{SIG_IGN} (ignore), or @code{#f} to restore whatever signal handler
1908 was installed before @code{sigaction} was first used. When a scheme
1909 procedure has been specified, that procedure will run in the given
1910 @var{thread}. When no thread has been given, the thread that made this
1911 call to @code{sigaction} is used.
1913 @var{flags} is a @code{logior} (@pxref{Bitwise Operations}) of the
1914 following (where provided by the system), or @code{0} for none.
1916 @defvar SA_NOCLDSTOP
1917 By default, @code{SIGCHLD} is signalled when a child process stops
1918 (ie.@: receives @code{SIGSTOP}), and when a child process terminates.
1919 With the @code{SA_NOCLDSTOP} flag, @code{SIGCHLD} is only signalled
1920 for termination, not stopping.
1922 @code{SA_NOCLDSTOP} has no effect on signals other than
1927 If a signal occurs while in a system call, deliver the signal then
1928 restart the system call (as opposed to returning an @code{EINTR} error
1932 The return value is a pair with information about the old handler as
1935 This interface does not provide access to the ``signal blocking''
1936 facility. Maybe this is not needed, since the thread support may
1937 provide solutions to the problem of consistent access to data
1941 @deffn {Scheme Procedure} restore-signals
1942 @deffnx {C Function} scm_restore_signals ()
1943 Return all signal handlers to the values they had before any call to
1944 @code{sigaction} was made. The return value is unspecified.
1947 @deffn {Scheme Procedure} alarm i
1948 @deffnx {C Function} scm_alarm (i)
1949 Set a timer to raise a @code{SIGALRM} signal after the specified
1950 number of seconds (an integer). It's advisable to install a signal
1952 @code{SIGALRM} beforehand, since the default action is to terminate
1955 The return value indicates the time remaining for the previous alarm,
1956 if any. The new value replaces the previous alarm. If there was
1957 no previous alarm, the return value is zero.
1960 @deffn {Scheme Procedure} pause
1961 @deffnx {C Function} scm_pause ()
1962 Pause the current process (thread?) until a signal arrives whose
1963 action is to either terminate the current process or invoke a
1964 handler procedure. The return value is unspecified.
1967 @deffn {Scheme Procedure} sleep secs
1968 @deffnx {Scheme Procedure} usleep usecs
1969 @deffnx {C Function} scm_sleep (secs)
1970 @deffnx {C Function} scm_usleep (usecs)
1971 Wait the given period @var{secs} seconds or @var{usecs} microseconds
1972 (both integers). If a signal arrives the wait stops and the return
1973 value is the time remaining, in seconds or microseconds respectively.
1974 If the period elapses with no signal the return is zero.
1976 On most systems the process scheduler is not microsecond accurate and
1977 the actual period slept by @code{usleep} might be rounded to a system
1978 clock tick boundary, which might be 10 milliseconds for instance.
1980 See @code{scm_std_sleep} and @code{scm_std_usleep} for equivalents at
1981 the C level (@pxref{Blocking}).
1984 @deffn {Scheme Procedure} getitimer which_timer
1985 @deffnx {Scheme Procedure} setitimer which_timer interval_seconds interval_microseconds periodic_seconds periodic_microseconds
1986 @deffnx {C Function} scm_getitimer (which_timer)
1987 @deffnx {C Function} scm_setitimer (which_timer, interval_seconds, interval_microseconds, periodic_seconds, periodic_microseconds)
1988 Get or set the periods programmed in certain system timers. These
1989 timers have a current interval value which counts down and on reaching
1990 zero raises a signal. An optional periodic value can be set to
1991 restart from there each time, for periodic operation.
1992 @var{which_timer} is one of the following values
1995 A real-time timer, counting down elapsed real time. At zero it raises
1996 @code{SIGALRM}. This is like @code{alarm} above, but with a higher
2000 @defvar ITIMER_VIRTUAL
2001 A virtual-time timer, counting down while the current process is
2002 actually using CPU. At zero it raises @code{SIGVTALRM}.
2006 A profiling timer, counting down while the process is running (like
2007 @code{ITIMER_VIRTUAL}) and also while system calls are running on the
2008 process's behalf. At zero it raises a @code{SIGPROF}.
2010 This timer is intended for profiling where a program is spending its
2011 time (by looking where it is when the timer goes off).
2014 @code{getitimer} returns the current timer value and its programmed
2015 restart value, as a list containing two pairs. Each pair is a time in
2016 seconds and microseconds: @code{((@var{interval_secs}
2017 . @var{interval_usecs}) (@var{periodic_secs}
2018 . @var{periodic_usecs}))}.
2020 @code{setitimer} sets the timer values similarly, in seconds and
2021 microseconds (which must be integers). The periodic value can be zero
2022 to have the timer run down just once. The return value is the timer's
2023 previous setting, in the same form as @code{getitimer} returns.
2026 (setitimer ITIMER_REAL
2027 5 500000 ;; first SIGALRM in 5.5 seconds time
2028 2 0) ;; then repeat every 2 seconds
2031 Although the timers are programmed in microseconds, the actual
2032 accuracy might not be that high.
2036 @node Terminals and Ptys
2037 @subsection Terminals and Ptys
2039 @deffn {Scheme Procedure} isatty? port
2040 @deffnx {C Function} scm_isatty_p (port)
2042 Return @code{#t} if @var{port} is using a serial non--file
2043 device, otherwise @code{#f}.
2046 @deffn {Scheme Procedure} ttyname port
2047 @deffnx {C Function} scm_ttyname (port)
2049 Return a string with the name of the serial terminal device
2050 underlying @var{port}.
2053 @deffn {Scheme Procedure} ctermid
2054 @deffnx {C Function} scm_ctermid ()
2056 Return a string containing the file name of the controlling
2057 terminal for the current process.
2060 @deffn {Scheme Procedure} tcgetpgrp port
2061 @deffnx {C Function} scm_tcgetpgrp (port)
2062 @cindex process group
2063 Return the process group ID of the foreground process group
2064 associated with the terminal open on the file descriptor
2065 underlying @var{port}.
2067 If there is no foreground process group, the return value is a
2068 number greater than 1 that does not match the process group ID
2069 of any existing process group. This can happen if all of the
2070 processes in the job that was formerly the foreground job have
2071 terminated, and no other job has yet been moved into the
2075 @deffn {Scheme Procedure} tcsetpgrp port pgid
2076 @deffnx {C Function} scm_tcsetpgrp (port, pgid)
2077 @cindex process group
2078 Set the foreground process group ID for the terminal used by the file
2079 descriptor underlying @var{port} to the integer @var{pgid}.
2081 must be a member of the same session as @var{pgid} and must have the same
2082 controlling terminal. The return value is unspecified.
2089 The following procedures are similar to the @code{popen} and
2090 @code{pclose} system routines. The code is in a separate ``popen''
2094 (use-modules (ice-9 popen))
2098 @deffn {Scheme Procedure} open-pipe command mode
2099 @deffnx {Scheme Procedure} open-pipe* mode prog [args...]
2100 Execute a command in a subprocess, with a pipe to it or from it, or
2101 with pipes in both directions.
2103 @code{open-pipe} runs the shell @var{command} using @samp{/bin/sh -c}.
2104 @code{open-pipe*} executes @var{prog} directly, with the optional
2105 @var{args} arguments (all strings).
2107 @var{mode} should be one of the following values. @code{OPEN_READ} is
2108 an input pipe, ie.@: to read from the subprocess. @code{OPEN_WRITE}
2109 is an output pipe, ie.@: to write to it.
2116 For an input pipe, the child's standard output is the pipe and
2117 standard input is inherited from @code{current-input-port}. For an
2118 output pipe, the child's standard input is the pipe and standard
2119 output is inherited from @code{current-output-port}. In all cases
2120 cases the child's standard error is inherited from
2121 @code{current-error-port} (@pxref{Default Ports}).
2123 If those @code{current-X-ports} are not files of some kind, and hence
2124 don't have file descriptors for the child, then @file{/dev/null} is
2127 Care should be taken with @code{OPEN_BOTH}, a deadlock will occur if
2128 both parent and child are writing, and waiting until the write
2129 completes before doing any reading. Each direction has
2130 @code{PIPE_BUF} bytes of buffering (@pxref{Ports and File
2131 Descriptors}), which will be enough for small writes, but not for say
2132 putting a big file through a filter.
2135 @deffn {Scheme Procedure} open-input-pipe command
2136 Equivalent to @code{open-pipe} with mode @code{OPEN_READ}.
2139 (let* ((port (open-input-pipe "date --utc"))
2140 (str (read-line port)))
2143 @result{} "Mon Mar 11 20:10:44 UTC 2002"
2147 @deffn {Scheme Procedure} open-output-pipe command
2148 Equivalent to @code{open-pipe} with mode @code{OPEN_WRITE}.
2151 (let ((port (open-output-pipe "lpr")))
2152 (display "Something for the line printer.\n" port)
2153 (if (not (eqv? 0 (status:exit-val (close-pipe port))))
2154 (error "Cannot print")))
2158 @deffn {Scheme Procedure} open-input-output-pipe command
2159 Equivalent to @code{open-pipe} with mode @code{OPEN_BOTH}.
2163 @deffn {Scheme Procedure} close-pipe port
2164 Close a pipe created by @code{open-pipe}, wait for the process to
2165 terminate, and return the wait status code. The status is as per
2166 @code{waitpid} and can be decoded with @code{status:exit-val} etc
2171 @code{waitpid WAIT_ANY} should not be used when pipes are open, since
2172 it can reap a pipe's child process, causing an error from a subsequent
2175 @code{close-port} (@pxref{Closing}) can close a pipe, but it doesn't
2176 reap the child process.
2178 The garbage collector will close a pipe no longer in use, and reap the
2179 child process with @code{waitpid}. If the child hasn't yet terminated
2180 the garbage collector doesn't block, but instead checks again in the
2183 Many systems have per-user and system-wide limits on the number of
2184 processes, and a system-wide limit on the number of pipes, so pipes
2185 should be closed explicitly when no longer needed, rather than letting
2186 the garbage collector pick them up at some later time.
2190 @subsection Networking
2194 * Network Address Conversion::
2195 * Network Databases::
2196 * Network Socket Address::
2197 * Network Sockets and Communication::
2198 * Internet Socket Examples::
2201 @node Network Address Conversion
2202 @subsubsection Network Address Conversion
2203 @cindex network address
2205 This section describes procedures which convert internet addresses
2206 between numeric and string formats.
2208 @subsubheading IPv4 Address Conversion
2211 An IPv4 Internet address is a 4-byte value, represented in Guile as an
2212 integer in host byte order, so that say ``0.0.0.1'' is 1, or
2213 ``1.0.0.0'' is 16777216.
2215 Some underlying C functions use network byte order for addresses,
2216 Guile converts as necessary so that at the Scheme level its host byte
2220 For a server, this can be used with @code{bind} (@pxref{Network
2221 Sockets and Communication}) to allow connections from any interface on
2225 @defvar INADDR_BROADCAST
2226 The broadcast address on the local network.
2229 @defvar INADDR_LOOPBACK
2230 The address of the local host using the loopback device, ie.@:
2234 @c INADDR_NONE is defined in the code, but serves no purpose.
2235 @c inet_addr() returns it as an error indication, but that function
2236 @c isn't provided, for the good reason that inet_aton() does the same
2237 @c job and gives an unambiguous error indication. (INADDR_NONE is a
2238 @c valid 4-byte value, in glibc it's the same as INADDR_BROADCAST.)
2240 @c @defvar INADDR_NONE
2244 @deffn {Scheme Procedure} inet-aton address
2245 @deffnx {C Function} scm_inet_aton (address)
2246 This function is deprecated in favor of @code{inet-pton}.
2248 Convert an IPv4 Internet address from printable string
2249 (dotted decimal notation) to an integer. E.g.,
2252 (inet-aton "127.0.0.1") @result{} 2130706433
2256 @deffn {Scheme Procedure} inet-ntoa inetid
2257 @deffnx {C Function} scm_inet_ntoa (inetid)
2258 This function is deprecated in favor of @code{inet-ntop}.
2260 Convert an IPv4 Internet address to a printable
2261 (dotted decimal notation) string. E.g.,
2264 (inet-ntoa 2130706433) @result{} "127.0.0.1"
2268 @deffn {Scheme Procedure} inet-netof address
2269 @deffnx {C Function} scm_inet_netof (address)
2270 Return the network number part of the given IPv4
2271 Internet address. E.g.,
2274 (inet-netof 2130706433) @result{} 127
2278 @deffn {Scheme Procedure} inet-lnaof address
2279 @deffnx {C Function} scm_lnaof (address)
2280 Return the local-address-with-network part of the given
2281 IPv4 Internet address, using the obsolete class A/B/C system.
2285 (inet-lnaof 2130706433) @result{} 1
2289 @deffn {Scheme Procedure} inet-makeaddr net lna
2290 @deffnx {C Function} scm_inet_makeaddr (net, lna)
2291 Make an IPv4 Internet address by combining the network number
2292 @var{net} with the local-address-within-network number
2296 (inet-makeaddr 127 1) @result{} 2130706433
2300 @subsubheading IPv6 Address Conversion
2303 An IPv6 Internet address is a 16-byte value, represented in Guile as
2304 an integer in host byte order, so that say ``::1'' is 1.
2306 @deffn {Scheme Procedure} inet-ntop family address
2307 @deffnx {C Function} scm_inet_ntop (family, address)
2308 Convert a network address from an integer to a printable string.
2309 @var{family} can be @code{AF_INET} or @code{AF_INET6}. E.g.,
2312 (inet-ntop AF_INET 2130706433) @result{} "127.0.0.1"
2313 (inet-ntop AF_INET6 (- (expt 2 128) 1))
2314 @result{} "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff"
2318 @deffn {Scheme Procedure} inet-pton family address
2319 @deffnx {C Function} scm_inet_pton (family, address)
2320 Convert a string containing a printable network address to an integer
2321 address. @var{family} can be @code{AF_INET} or @code{AF_INET6}.
2325 (inet-pton AF_INET "127.0.0.1") @result{} 2130706433
2326 (inet-pton AF_INET6 "::1") @result{} 1
2331 @node Network Databases
2332 @subsubsection Network Databases
2333 @cindex network database
2335 This section describes procedures which query various network databases.
2336 Care should be taken when using the database routines since they are not
2339 @subsubheading @code{getaddrinfo}
2341 @cindex @code{addrinfo} object type
2342 @cindex host name lookup
2343 @cindex service name lookup
2345 The @code{getaddrinfo} procedure maps host and service names to socket addresses
2346 and associated information in a protocol-independent way.
2348 @deffn {Scheme Procedure} getaddrinfo name service [hint_flags [hint_family [hint_socktype [hint_protocol]]]]
2349 @deffnx {C Function} scm_getaddrinfo (name, service, hint_flags, hint_family, hint_socktype, hint_protocol)
2350 Return a list of @code{addrinfo} structures containing
2351 a socket address and associated information for host @var{name}
2352 and/or @var{service} to be used in creating a socket with
2353 which to address the specified service.
2356 (let* ((ai (car (getaddrinfo "www.gnu.org" "http")))
2357 (s (socket (addrinfo:fam ai) (addrinfo:socktype ai)
2358 (addrinfo:protocol ai))))
2359 (connect s (addrinfo:addr ai))
2363 When @var{service} is omitted or is @code{#f}, return
2364 network-level addresses for @var{name}. When @var{name}
2365 is @code{#f} @var{service} must be provided and service
2366 locations local to the caller are returned.
2368 Additional hints can be provided. When specified,
2369 @var{hint_flags} should be a bitwise-or of zero or more
2370 constants among the following:
2374 Socket address is intended for @code{bind}.
2377 Request for canonical host name, available via
2378 @code{addrinfo:canonname}. This makes sense mainly when
2379 DNS lookups are involved.
2381 @item AI_NUMERICHOST
2382 Specifies that @var{name} is a numeric host address string
2383 (e.g., @code{"127.0.0.1"}), meaning that name resolution
2386 @item AI_NUMERICSERV
2387 Likewise, specifies that @var{service} is a numeric port
2388 string (e.g., @code{"80"}).
2391 Return only addresses configured on the local system It is
2392 highly recommended to provide this flag when the returned
2393 socket addresses are to be used to make connections;
2394 otherwise, some of the returned addresses could be unreachable
2395 or use a protocol that is not supported.
2398 When looking up IPv6 addresses, return mapped IPv4 addresses if
2399 there is no IPv6 address available at all.
2402 If this flag is set along with @code{AI_V4MAPPED} when looking up IPv6
2403 addresses, return all IPv6 addresses as well as all IPv4 addresses, the latter
2404 mapped to IPv6 format.
2407 When given, @var{hint_family} should specify the requested
2408 address family, e.g., @code{AF_INET6}. Similarly,
2409 @var{hint_socktype} should specify the requested socket type
2410 (e.g., @code{SOCK_DGRAM}), and @var{hint_protocol} should
2411 specify the requested protocol (its value is interpretered
2412 as in calls to @code{socket}).
2414 On error, an exception with key @code{getaddrinfo-error} is
2415 thrown, with an error code (an integer) as its argument:
2418 (catch 'getaddrinfo-error
2420 (getaddrinfo "www.gnu.org" "gopher"))
2421 (lambda (key errcode)
2422 (cond ((= errcode EAI_SERVICE)
2423 (display "doesn't know about Gopher!\n"))
2424 ((= errcode EAI_NONAME)
2425 (display "www.gnu.org not found\\n"))
2427 (format #t "something wrong: ~a\n"
2428 (gai-strerror errcode))))))
2435 The name or service could not be resolved at this time. Future
2436 attempts may succeed.
2439 @var{hint_flags} contains an invalid value.
2442 A non-recoverable error occurred when attempting to
2446 @var{hint_family} was not recognized.
2449 Either @var{name} does not resolve for the supplied parameters,
2450 or neither @var{name} nor @var{service} were supplied.
2453 @var{service} was not recognized for the specified socket type.
2456 @var{hint_socktype} was not recognized.
2459 A system error occurred; the error code can be found in
2463 Users are encouraged to read the
2464 @url{http://www.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html,
2465 "POSIX specification} for more details.
2468 The following procedures take an @code{addrinfo} object as returned by
2471 @deffn {Scheme Procedure} addrinfo:flags ai
2472 Return flags for @var{ai} as a bitwise or of @code{AI_} values (see above).
2475 @deffn {Scheme Procedure} addrinfo:fam ai
2476 Return the address family of @var{ai} (a @code{AF_} value).
2479 @deffn {Scheme Procedure} addrinfo:socktype ai
2480 Return the socket type for @var{ai} (a @code{SOCK_} value).
2483 @deffn {Scheme Procedure} addrinfo:protocol ai
2484 Return the protocol of @var{ai}.
2487 @deffn {Scheme Procedure} addrinfo:addr ai
2488 Return the socket address associated with @var{ai} as a @code{sockaddr}
2489 object (@pxref{Network Socket Address}).
2492 @deffn {Scheme Procedure} addrinfo:canonname ai
2493 Return a string for the canonical name associated with @var{ai} if
2494 the @code{AI_CANONNAME} flag was supplied.
2497 @subsubheading The Host Database
2498 @cindex @file{/etc/hosts}
2499 @cindex network database
2501 A @dfn{host object} is a structure that represents what is known about a
2502 network host, and is the usual way of representing a system's network
2503 identity inside software.
2505 The following functions accept a host object and return a selected
2508 @deffn {Scheme Procedure} hostent:name host
2509 The ``official'' hostname for @var{host}.
2511 @deffn {Scheme Procedure} hostent:aliases host
2512 A list of aliases for @var{host}.
2514 @deffn {Scheme Procedure} hostent:addrtype host
2515 The host address type, one of the @code{AF} constants, such as
2516 @code{AF_INET} or @code{AF_INET6}.
2518 @deffn {Scheme Procedure} hostent:length host
2519 The length of each address for @var{host}, in bytes.
2521 @deffn {Scheme Procedure} hostent:addr-list host
2522 The list of network addresses associated with @var{host}. For
2523 @code{AF_INET} these are integer IPv4 address (@pxref{Network Address
2527 The following procedures can be used to search the host database. However,
2528 @code{getaddrinfo} should be preferred over them since it's more generic and
2531 @deffn {Scheme Procedure} gethost [host]
2532 @deffnx {Scheme Procedure} gethostbyname hostname
2533 @deffnx {Scheme Procedure} gethostbyaddr address
2534 @deffnx {C Function} scm_gethost (host)
2535 Look up a host by name or address, returning a host object. The
2536 @code{gethost} procedure will accept either a string name or an integer
2537 address; if given no arguments, it behaves like @code{gethostent} (see
2538 below). If a name or address is supplied but the address can not be
2539 found, an error will be thrown to one of the keys:
2540 @code{host-not-found}, @code{try-again}, @code{no-recovery} or
2541 @code{no-data}, corresponding to the equivalent @code{h_error} values.
2542 Unusual conditions may result in errors thrown to the
2543 @code{system-error} or @code{misc_error} keys.
2546 (gethost "www.gnu.org")
2547 @result{} #("www.gnu.org" () 2 4 (3353880842))
2549 (gethostbyname "www.emacs.org")
2550 @result{} #("emacs.org" ("www.emacs.org") 2 4 (1073448978))
2554 The following procedures may be used to step through the host
2555 database from beginning to end.
2557 @deffn {Scheme Procedure} sethostent [stayopen]
2558 Initialize an internal stream from which host objects may be read. This
2559 procedure must be called before any calls to @code{gethostent}, and may
2560 also be called afterward to reset the host entry stream. If
2561 @var{stayopen} is supplied and is not @code{#f}, the database is not
2562 closed by subsequent @code{gethostbyname} or @code{gethostbyaddr} calls,
2563 possibly giving an efficiency gain.
2566 @deffn {Scheme Procedure} gethostent
2567 Return the next host object from the host database, or @code{#f} if
2568 there are no more hosts to be found (or an error has been encountered).
2569 This procedure may not be used before @code{sethostent} has been called.
2572 @deffn {Scheme Procedure} endhostent
2573 Close the stream used by @code{gethostent}. The return value is unspecified.
2576 @deffn {Scheme Procedure} sethost [stayopen]
2577 @deffnx {C Function} scm_sethost (stayopen)
2578 If @var{stayopen} is omitted, this is equivalent to @code{endhostent}.
2579 Otherwise it is equivalent to @code{sethostent stayopen}.
2582 @subsubheading The Network Database
2583 @cindex network database
2585 The following functions accept an object representing a network
2586 and return a selected component:
2588 @deffn {Scheme Procedure} netent:name net
2589 The ``official'' network name.
2591 @deffn {Scheme Procedure} netent:aliases net
2592 A list of aliases for the network.
2594 @deffn {Scheme Procedure} netent:addrtype net
2595 The type of the network number. Currently, this returns only
2598 @deffn {Scheme Procedure} netent:net net
2602 The following procedures are used to search the network database:
2604 @deffn {Scheme Procedure} getnet [net]
2605 @deffnx {Scheme Procedure} getnetbyname net-name
2606 @deffnx {Scheme Procedure} getnetbyaddr net-number
2607 @deffnx {C Function} scm_getnet (net)
2608 Look up a network by name or net number in the network database. The
2609 @var{net-name} argument must be a string, and the @var{net-number}
2610 argument must be an integer. @code{getnet} will accept either type of
2611 argument, behaving like @code{getnetent} (see below) if no arguments are
2615 The following procedures may be used to step through the network
2616 database from beginning to end.
2618 @deffn {Scheme Procedure} setnetent [stayopen]
2619 Initialize an internal stream from which network objects may be read. This
2620 procedure must be called before any calls to @code{getnetent}, and may
2621 also be called afterward to reset the net entry stream. If
2622 @var{stayopen} is supplied and is not @code{#f}, the database is not
2623 closed by subsequent @code{getnetbyname} or @code{getnetbyaddr} calls,
2624 possibly giving an efficiency gain.
2627 @deffn {Scheme Procedure} getnetent
2628 Return the next entry from the network database.
2631 @deffn {Scheme Procedure} endnetent
2632 Close the stream used by @code{getnetent}. The return value is unspecified.
2635 @deffn {Scheme Procedure} setnet [stayopen]
2636 @deffnx {C Function} scm_setnet (stayopen)
2637 If @var{stayopen} is omitted, this is equivalent to @code{endnetent}.
2638 Otherwise it is equivalent to @code{setnetent stayopen}.
2641 @subsubheading The Protocol Database
2642 @cindex @file{/etc/protocols}
2644 @cindex network protocols
2646 The following functions accept an object representing a protocol
2647 and return a selected component:
2649 @deffn {Scheme Procedure} protoent:name protocol
2650 The ``official'' protocol name.
2652 @deffn {Scheme Procedure} protoent:aliases protocol
2653 A list of aliases for the protocol.
2655 @deffn {Scheme Procedure} protoent:proto protocol
2656 The protocol number.
2659 The following procedures are used to search the protocol database:
2661 @deffn {Scheme Procedure} getproto [protocol]
2662 @deffnx {Scheme Procedure} getprotobyname name
2663 @deffnx {Scheme Procedure} getprotobynumber number
2664 @deffnx {C Function} scm_getproto (protocol)
2665 Look up a network protocol by name or by number. @code{getprotobyname}
2666 takes a string argument, and @code{getprotobynumber} takes an integer
2667 argument. @code{getproto} will accept either type, behaving like
2668 @code{getprotoent} (see below) if no arguments are supplied.
2671 The following procedures may be used to step through the protocol
2672 database from beginning to end.
2674 @deffn {Scheme Procedure} setprotoent [stayopen]
2675 Initialize an internal stream from which protocol objects may be read. This
2676 procedure must be called before any calls to @code{getprotoent}, and may
2677 also be called afterward to reset the protocol entry stream. If
2678 @var{stayopen} is supplied and is not @code{#f}, the database is not
2679 closed by subsequent @code{getprotobyname} or @code{getprotobynumber} calls,
2680 possibly giving an efficiency gain.
2683 @deffn {Scheme Procedure} getprotoent
2684 Return the next entry from the protocol database.
2687 @deffn {Scheme Procedure} endprotoent
2688 Close the stream used by @code{getprotoent}. The return value is unspecified.
2691 @deffn {Scheme Procedure} setproto [stayopen]
2692 @deffnx {C Function} scm_setproto (stayopen)
2693 If @var{stayopen} is omitted, this is equivalent to @code{endprotoent}.
2694 Otherwise it is equivalent to @code{setprotoent stayopen}.
2697 @subsubheading The Service Database
2698 @cindex @file{/etc/services}
2700 @cindex network services
2702 The following functions accept an object representing a service
2703 and return a selected component:
2705 @deffn {Scheme Procedure} servent:name serv
2706 The ``official'' name of the network service.
2708 @deffn {Scheme Procedure} servent:aliases serv
2709 A list of aliases for the network service.
2711 @deffn {Scheme Procedure} servent:port serv
2712 The Internet port used by the service.
2714 @deffn {Scheme Procedure} servent:proto serv
2715 The protocol used by the service. A service may be listed many times
2716 in the database under different protocol names.
2719 The following procedures are used to search the service database:
2721 @deffn {Scheme Procedure} getserv [name [protocol]]
2722 @deffnx {Scheme Procedure} getservbyname name protocol
2723 @deffnx {Scheme Procedure} getservbyport port protocol
2724 @deffnx {C Function} scm_getserv (name, protocol)
2725 Look up a network service by name or by service number, and return a
2726 network service object. The @var{protocol} argument specifies the name
2727 of the desired protocol; if the protocol found in the network service
2728 database does not match this name, a system error is signalled.
2730 The @code{getserv} procedure will take either a service name or number
2731 as its first argument; if given no arguments, it behaves like
2732 @code{getservent} (see below).
2735 (getserv "imap" "tcp")
2736 @result{} #("imap2" ("imap") 143 "tcp")
2738 (getservbyport 88 "udp")
2739 @result{} #("kerberos" ("kerberos5" "krb5") 88 "udp")
2743 The following procedures may be used to step through the service
2744 database from beginning to end.
2746 @deffn {Scheme Procedure} setservent [stayopen]
2747 Initialize an internal stream from which service objects may be read. This
2748 procedure must be called before any calls to @code{getservent}, and may
2749 also be called afterward to reset the service entry stream. If
2750 @var{stayopen} is supplied and is not @code{#f}, the database is not
2751 closed by subsequent @code{getservbyname} or @code{getservbyport} calls,
2752 possibly giving an efficiency gain.
2755 @deffn {Scheme Procedure} getservent
2756 Return the next entry from the services database.
2759 @deffn {Scheme Procedure} endservent
2760 Close the stream used by @code{getservent}. The return value is unspecified.
2763 @deffn {Scheme Procedure} setserv [stayopen]
2764 @deffnx {C Function} scm_setserv (stayopen)
2765 If @var{stayopen} is omitted, this is equivalent to @code{endservent}.
2766 Otherwise it is equivalent to @code{setservent stayopen}.
2770 @node Network Socket Address
2771 @subsubsection Network Socket Address
2772 @cindex socket address
2773 @cindex network socket address
2774 @tpindex Socket address
2776 A @dfn{socket address} object identifies a socket endpoint for
2777 communication. In the case of @code{AF_INET} for instance, the socket
2778 address object comprises the host address (or interface on the host)
2779 and a port number which specifies a particular open socket in a
2780 running client or server process. A socket address object can be
2783 @deffn {Scheme Procedure} make-socket-address AF_INET ipv4addr port
2784 @deffnx {Scheme Procedure} make-socket-address AF_INET6 ipv6addr port [flowinfo [scopeid]]
2785 @deffnx {Scheme Procedure} make-socket-address AF_UNIX path
2786 @deffnx {C Function} scm_make_socket_address family address arglist
2787 Return a new socket address object. The first argument is the address
2788 family, one of the @code{AF} constants, then the arguments vary
2789 according to the family.
2791 For @code{AF_INET} the arguments are an IPv4 network address number
2792 (@pxref{Network Address Conversion}), and a port number.
2794 For @code{AF_INET6} the arguments are an IPv6 network address number
2795 and a port number. Optional @var{flowinfo} and @var{scopeid}
2796 arguments may be given (both integers, default 0).
2798 For @code{AF_UNIX} the argument is a filename (a string).
2800 The C function @code{scm_make_socket_address} takes the @var{family}
2801 and @var{address} arguments directly, then @var{arglist} is a list of
2802 further arguments, being the port for IPv4, port and optional flowinfo
2803 and scopeid for IPv6, or the empty list @code{SCM_EOL} for Unix
2808 The following functions access the fields of a socket address object,
2810 @deffn {Scheme Procedure} sockaddr:fam sa
2811 Return the address family from socket address object @var{sa}. This
2812 is one of the @code{AF} constants (eg. @code{AF_INET}).
2815 @deffn {Scheme Procedure} sockaddr:path sa
2816 For an @code{AF_UNIX} socket address object @var{sa}, return the
2820 @deffn {Scheme Procedure} sockaddr:addr sa
2821 For an @code{AF_INET} or @code{AF_INET6} socket address object
2822 @var{sa}, return the network address number.
2825 @deffn {Scheme Procedure} sockaddr:port sa
2826 For an @code{AF_INET} or @code{AF_INET6} socket address object
2827 @var{sa}, return the port number.
2830 @deffn {Scheme Procedure} sockaddr:flowinfo sa
2831 For an @code{AF_INET6} socket address object @var{sa}, return the
2835 @deffn {Scheme Procedure} sockaddr:scopeid sa
2836 For an @code{AF_INET6} socket address object @var{sa}, return the
2840 @tpindex @code{struct sockaddr}
2841 @tpindex @code{sockaddr}
2842 The functions below convert to and from the C @code{struct sockaddr}
2843 (@pxref{Address Formats,,, libc, The GNU C Library Reference Manual}).
2844 That structure is a generic type, an application can cast to or from
2845 @code{struct sockaddr_in}, @code{struct sockaddr_in6} or @code{struct
2846 sockaddr_un} according to the address family.
2848 In a @code{struct sockaddr} taken or returned, the byte ordering in
2849 the fields follows the C conventions (@pxref{Byte Order,, Byte Order
2850 Conversion, libc, The GNU C Library Reference Manual}). This means
2851 network byte order for @code{AF_INET} host address
2852 (@code{sin_addr.s_addr}) and port number (@code{sin_port}), and
2853 @code{AF_INET6} port number (@code{sin6_port}). But at the Scheme
2854 level these values are taken or returned in host byte order, so the
2855 port is an ordinary integer, and the host address likewise is an
2856 ordinary integer (as described in @ref{Network Address Conversion}).
2858 @deftypefn {C Function} {struct sockaddr *} scm_c_make_socket_address (SCM family, SCM address, SCM args, size_t *outsize)
2859 Return a newly-@code{malloc}ed @code{struct sockaddr} created from
2860 arguments like those taken by @code{scm_make_socket_address} above.
2862 The size (in bytes) of the @code{struct sockaddr} return is stored
2863 into @code{*@var{outsize}}. An application must call @code{free} to
2864 release the returned structure when no longer required.
2867 @deftypefn {C Function} SCM scm_from_sockaddr (const struct sockaddr *address, unsigned address_size)
2868 Return a Scheme socket address object from the C @var{address}
2869 structure. @var{address_size} is the size in bytes of @var{address}.
2872 @deftypefn {C Function} {struct sockaddr *} scm_to_sockaddr (SCM address, size_t *address_size)
2873 Return a newly-@code{malloc}ed @code{struct sockaddr} from a Scheme
2874 level socket address object.
2876 The size (in bytes) of the @code{struct sockaddr} return is stored
2877 into @code{*@var{outsize}}. An application must call @code{free} to
2878 release the returned structure when no longer required.
2882 @node Network Sockets and Communication
2883 @subsubsection Network Sockets and Communication
2885 @cindex network socket
2887 Socket ports can be created using @code{socket} and @code{socketpair}.
2888 The ports are initially unbuffered, to make reading and writing to the
2889 same port more reliable. A buffer can be added to the port using
2890 @code{setvbuf}; see @ref{Ports and File Descriptors}.
2892 Most systems have limits on how many files and sockets can be open, so
2893 it's strongly recommended that socket ports be closed explicitly when
2894 no longer required (@pxref{Ports}).
2896 Some of the underlying C functions take values in network byte order,
2897 but the convention in Guile is that at the Scheme level everything is
2898 ordinary host byte order and conversions are made automatically where
2901 @deffn {Scheme Procedure} socket family style proto
2902 @deffnx {C Function} scm_socket (family, style, proto)
2903 Return a new socket port of the type specified by @var{family},
2904 @var{style} and @var{proto}. All three parameters are integers. The
2905 possible values for @var{family} are as follows, where supported by
2913 The possible values for @var{style} are as follows, again where
2914 supported by the system,
2920 @defvarx SOCK_SEQPACKET
2923 @var{proto} can be obtained from a protocol name using
2924 @code{getprotobyname} (@pxref{Network Databases}). A value of zero
2925 means the default protocol, which is usually right.
2927 A socket cannot by used for communication until it has been connected
2928 somewhere, usually with either @code{connect} or @code{accept} below.
2931 @deffn {Scheme Procedure} socketpair family style proto
2932 @deffnx {C Function} scm_socketpair (family, style, proto)
2933 Return a pair, the @code{car} and @code{cdr} of which are two unnamed
2934 socket ports connected to each other. The connection is full-duplex,
2935 so data can be transferred in either direction between the two.
2937 @var{family}, @var{style} and @var{proto} are as per @code{socket}
2938 above. But many systems only support socket pairs in the
2939 @code{PF_UNIX} family. Zero is likely to be the only meaningful value
2943 @deffn {Scheme Procedure} getsockopt sock level optname
2944 @deffnx {Scheme Procedure} setsockopt sock level optname value
2945 @deffnx {C Function} scm_getsockopt (sock, level, optname)
2946 @deffnx {C Function} scm_setsockopt (sock, level, optname, value)
2947 Get or set an option on socket port @var{sock}. @code{getsockopt}
2948 returns the current value. @code{setsockopt} sets a value and the
2949 return is unspecified.
2951 @var{level} is an integer specifying a protocol layer, either
2952 @code{SOL_SOCKET} for socket level options, or a protocol number from
2953 the @code{IPPROTO} constants or @code{getprotoent} (@pxref{Network
2958 @defvarx IPPROTO_TCP
2959 @defvarx IPPROTO_UDP
2962 @var{optname} is an integer specifying an option within the protocol
2965 For @code{SOL_SOCKET} level the following @var{optname}s are defined
2966 (when provided by the system). For their meaning see
2967 @ref{Socket-Level Options,,, libc, The GNU C Library Reference
2968 Manual}, or @command{man 7 socket}.
2971 @defvarx SO_REUSEADDR
2975 @defvarx SO_DONTROUTE
2976 @defvarx SO_BROADCAST
2979 @defvarx SO_KEEPALIVE
2980 @defvarx SO_OOBINLINE
2981 @defvarx SO_NO_CHECK
2982 @defvarx SO_PRIORITY
2983 The @var{value} taken or returned is an integer.
2987 The @var{value} taken or returned is a pair of integers
2988 @code{(@var{ENABLE} . @var{TIMEOUT})}. On old systems without timeout
2989 support (ie.@: without @code{struct linger}), only @var{ENABLE} has an
2990 effect but the value in Guile is always a pair.
2993 @c Note that we refer only to ``man ip'' here. On GNU/Linux it's
2994 @c ``man 7 ip'' but on NetBSD it's ``man 4 ip''.
2996 For IP level (@code{IPPROTO_IP}) the following @var{optname}s are
2997 defined (when provided by the system). See @command{man ip} for what
3000 @defvar IP_ADD_MEMBERSHIP
3001 @defvarx IP_DROP_MEMBERSHIP
3002 These can be used only with @code{setsockopt}, not @code{getsockopt}.
3003 @var{value} is a pair @code{(@var{MULTIADDR} . @var{INTERFACEADDR})}
3004 of integer IPv4 addresses (@pxref{Network Address Conversion}).
3005 @var{MULTIADDR} is a multicast address to be added to or dropped from
3006 the interface @var{INTERFACEADDR}. @var{INTERFACEADDR} can be
3007 @code{INADDR_ANY} to have the system select the interface.
3008 @var{INTERFACEADDR} can also be an interface index number, on systems
3013 @deffn {Scheme Procedure} shutdown sock how
3014 @deffnx {C Function} scm_shutdown (sock, how)
3015 Sockets can be closed simply by using @code{close-port}. The
3016 @code{shutdown} procedure allows reception or transmission on a
3017 connection to be shut down individually, according to the parameter
3022 Stop receiving data for this socket. If further data arrives, reject it.
3024 Stop trying to transmit data from this socket. Discard any
3025 data waiting to be sent. Stop looking for acknowledgement of
3026 data already sent; don't retransmit it if it is lost.
3028 Stop both reception and transmission.
3031 The return value is unspecified.
3034 @deffn {Scheme Procedure} connect sock sockaddr
3035 @deffnx {Scheme Procedure} connect sock AF_INET ipv4addr port
3036 @deffnx {Scheme Procedure} connect sock AF_INET6 ipv6addr port [flowinfo [scopeid]]
3037 @deffnx {Scheme Procedure} connect sock AF_UNIX path
3038 @deffnx {C Function} scm_connect (sock, fam, address, args)
3039 Initiate a connection on socket port @var{sock} to a given address.
3040 The destination is either a socket address object, or arguments the
3041 same as @code{make-socket-address} would take to make such an object
3042 (@pxref{Network Socket Address}). The return value is unspecified.
3045 (connect sock AF_INET INADDR_LOOPBACK 23)
3046 (connect sock (make-socket-address AF_INET INADDR_LOOPBACK 23))
3050 @deffn {Scheme Procedure} bind sock sockaddr
3051 @deffnx {Scheme Procedure} bind sock AF_INET ipv4addr port
3052 @deffnx {Scheme Procedure} bind sock AF_INET6 ipv6addr port [flowinfo [scopeid]]
3053 @deffnx {Scheme Procedure} bind sock AF_UNIX path
3054 @deffnx {C Function} scm_bind (sock, fam, address, args)
3055 Bind socket port @var{sock} to the given address. The address is
3056 either a socket address object, or arguments the same as
3057 @code{make-socket-address} would take to make such an object
3058 (@pxref{Network Socket Address}). The return value is unspecified.
3060 Generally a socket is only explicitly bound to a particular address
3061 when making a server, ie. to listen on a particular port. For an
3062 outgoing connection the system will assign a local address
3063 automatically, if not already bound.
3066 (bind sock AF_INET INADDR_ANY 12345)
3067 (bind sock (make-socket-address AF_INET INADDR_ANY 12345))
3071 @deffn {Scheme Procedure} listen sock backlog
3072 @deffnx {C Function} scm_listen (sock, backlog)
3073 Enable @var{sock} to accept connection
3074 requests. @var{backlog} is an integer specifying
3075 the maximum length of the queue for pending connections.
3076 If the queue fills, new clients will fail to connect until
3077 the server calls @code{accept} to accept a connection from
3080 The return value is unspecified.
3083 @deffn {Scheme Procedure} accept sock
3084 @deffnx {C Function} scm_accept (sock)
3085 Accept a connection from socket port @var{sock} which has been enabled
3086 for listening with @code{listen} above. If there are no incoming
3087 connections in the queue, wait until one is available (unless
3088 @code{O_NONBLOCK} has been set on the socket, @pxref{Ports and File
3089 Descriptors,@code{fcntl}}).
3091 The return value is a pair. The @code{car} is a new socket port,
3092 connected and ready to communicate. The @code{cdr} is a socket
3093 address object (@pxref{Network Socket Address}) which is where the
3094 remote connection is from (like @code{getpeername} below).
3096 All communication takes place using the new socket returned. The
3097 given @var{sock} remains bound and listening, and @code{accept} may be
3098 called on it again to get another incoming connection when desired.
3101 @deffn {Scheme Procedure} getsockname sock
3102 @deffnx {C Function} scm_getsockname (sock)
3103 Return a socket address object which is the where @var{sock} is bound
3104 locally. @var{sock} may have obtained its local address from
3105 @code{bind} (above), or if a @code{connect} is done with an otherwise
3106 unbound socket (which is usual) then the system will have assigned an
3109 Note that on many systems the address of a socket in the
3110 @code{AF_UNIX} namespace cannot be read.
3113 @deffn {Scheme Procedure} getpeername sock
3114 @deffnx {C Function} scm_getpeername (sock)
3115 Return a socket address object which is where @var{sock} is connected
3116 to, ie. the remote endpoint.
3118 Note that on many systems the address of a socket in the
3119 @code{AF_UNIX} namespace cannot be read.
3122 @deffn {Scheme Procedure} recv! sock buf [flags]
3123 @deffnx {C Function} scm_recv (sock, buf, flags)
3124 Receive data from a socket port.
3125 @var{sock} must already
3126 be bound to the address from which data is to be received.
3127 @var{buf} is a string into which
3128 the data will be written. The size of @var{buf} limits
3130 data which can be received: in the case of packet
3131 protocols, if a packet larger than this limit is encountered
3133 will be irrevocably lost.
3137 @vindex MSG_DONTROUTE
3138 The optional @var{flags} argument is a value or bitwise OR of
3139 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3141 The value returned is the number of bytes read from the
3144 Note that the data is read directly from the socket file
3146 any unread buffered port data is ignored.
3149 @deffn {Scheme Procedure} send sock message [flags]
3150 @deffnx {C Function} scm_send (sock, message, flags)
3153 @vindex MSG_DONTROUTE
3154 Transmit the string @var{message} on a socket port @var{sock}.
3155 @var{sock} must already be bound to a destination address. The value
3156 returned is the number of bytes transmitted---it's possible for this
3157 to be less than the length of @var{message} if the socket is set to be
3158 non-blocking. The optional @var{flags} argument is a value or bitwise
3159 OR of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3161 Note that the data is written directly to the socket
3163 any unflushed buffered port data is ignored.
3166 @deffn {Scheme Procedure} recvfrom! sock str [flags [start [end]]]
3167 @deffnx {C Function} scm_recvfrom (sock, str, flags, start, end)
3168 Receive data from socket port @var{sock}, returning the originating
3169 address as well as the data. This function is usually for datagram
3170 sockets, but can be used on stream-oriented sockets too.
3172 The data received is stored in the given @var{str}, the whole string
3173 or just the region between the optional @var{start} and @var{end}
3174 positions. The size of @var{str} limits the amount of data which can
3175 be received. For datagram protocols if a packet larger than this is
3176 received then excess bytes are irrevocably lost.
3178 The return value is a pair. The @code{car} is the number of bytes
3179 read. The @code{cdr} is a socket address object (@pxref{Network
3180 Socket Address}) which is where the data came from, or @code{#f} if
3181 the origin is unknown.
3185 @vindex MSG_DONTROUTE
3186 The optional @var{flags} argument is a or bitwise-OR (@code{logior})
3187 of @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3189 Data is read directly from the socket file descriptor, any buffered
3190 port data is ignored.
3192 @c This was linux kernel 2.6.15 and glibc 2.3.6, not sure what any
3193 @c specs are supposed to say about recvfrom threading.
3195 On a GNU/Linux system @code{recvfrom!} is not multi-threading, all
3196 threads stop while a @code{recvfrom!} call is in progress. An
3197 application may need to use @code{select}, @code{O_NONBLOCK} or
3198 @code{MSG_DONTWAIT} to avoid this.
3201 @deffn {Scheme Procedure} sendto sock message sockaddr [flags]
3202 @deffnx {Scheme Procedure} sendto sock message AF_INET ipv4addr port [flags]
3203 @deffnx {Scheme Procedure} sendto sock message AF_INET6 ipv6addr port [flowinfo [scopeid [flags]]]
3204 @deffnx {Scheme Procedure} sendto sock message AF_UNIX path [flags]
3205 @deffnx {C Function} scm_sendto (sock, message, fam, address, args_and_flags)
3206 Transmit the string @var{message} as a datagram on socket port
3207 @var{sock}. The destination is specified either as a socket address
3208 object, or as arguments the same as would be taken by
3209 @code{make-socket-address} to create such an object (@pxref{Network
3212 The destination address may be followed by an optional @var{flags}
3213 argument which is a @code{logior} (@pxref{Bitwise Operations}) of
3214 @code{MSG_OOB}, @code{MSG_PEEK}, @code{MSG_DONTROUTE} etc.
3216 The value returned is the number of bytes transmitted --
3218 this to be less than the length of @var{message} if the
3220 set to be non-blocking.
3221 Note that the data is written directly to the socket
3223 any unflushed buffered port data is ignored.
3226 The following functions can be used to convert short and long integers
3227 between ``host'' and ``network'' order. Although the procedures above do
3228 this automatically for addresses, the conversion will still need to
3229 be done when sending or receiving encoded integer data from the network.
3231 @deffn {Scheme Procedure} htons value
3232 @deffnx {C Function} scm_htons (value)
3233 Convert a 16 bit quantity from host to network byte ordering.
3234 @var{value} is packed into 2 bytes, which are then converted
3235 and returned as a new integer.
3238 @deffn {Scheme Procedure} ntohs value
3239 @deffnx {C Function} scm_ntohs (value)
3240 Convert a 16 bit quantity from network to host byte ordering.
3241 @var{value} is packed into 2 bytes, which are then converted
3242 and returned as a new integer.
3245 @deffn {Scheme Procedure} htonl value
3246 @deffnx {C Function} scm_htonl (value)
3247 Convert a 32 bit quantity from host to network byte ordering.
3248 @var{value} is packed into 4 bytes, which are then converted
3249 and returned as a new integer.
3252 @deffn {Scheme Procedure} ntohl value
3253 @deffnx {C Function} scm_ntohl (value)
3254 Convert a 32 bit quantity from network to host byte ordering.
3255 @var{value} is packed into 4 bytes, which are then converted
3256 and returned as a new integer.
3259 These procedures are inconvenient to use at present, but consider:
3262 (define write-network-long
3263 (lambda (value port)
3264 (let ((v (make-uniform-vector 1 1 0)))
3265 (uniform-vector-set! v 0 (htonl value))
3266 (uniform-vector-write v port))))
3268 (define read-network-long
3270 (let ((v (make-uniform-vector 1 1 0)))
3271 (uniform-vector-read! v port)
3272 (ntohl (uniform-vector-ref v 0)))))
3276 @node Internet Socket Examples
3277 @subsubsection Network Socket Examples
3278 @cindex network examples
3279 @cindex socket examples
3281 The following give examples of how to use network sockets.
3283 @subsubheading Internet Socket Client Example
3285 @cindex socket client example
3286 The following example demonstrates an Internet socket client.
3287 It connects to the HTTP daemon running on the local machine and
3288 returns the contents of the root index URL.
3291 (let ((s (socket PF_INET SOCK_STREAM 0)))
3292 (connect s AF_INET (inet-pton AF_INET "127.0.0.1") 80)
3293 (display "GET / HTTP/1.0\r\n\r\n" s)
3295 (do ((line (read-line s) (read-line s)))
3296 ((eof-object? line))
3302 @subsubheading Internet Socket Server Example
3304 @cindex socket server example
3305 The following example shows a simple Internet server which listens on
3306 port 2904 for incoming connections and sends a greeting back to the
3310 (let ((s (socket PF_INET SOCK_STREAM 0)))
3311 (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
3312 ;; @r{Specific address?}
3313 ;; @r{(bind s AF_INET (inet-pton AF_INET "127.0.0.1") 2904)}
3314 (bind s AF_INET INADDR_ANY 2904)
3317 (simple-format #t "Listening for clients in pid: ~S" (getpid))
3321 (let* ((client-connection (accept s))
3322 (client-details (cdr client-connection))
3323 (client (car client-connection)))
3324 (simple-format #t "Got new client connection: ~S"
3327 (simple-format #t "Client address: ~S"
3329 (sockaddr:addr client-details)))
3331 ;; @r{Send back the greeting to the client port}
3332 (display "Hello client\r\n" client)
3337 @node System Identification
3338 @subsection System Identification
3341 This section lists the various procedures Guile provides for accessing
3342 information about the system it runs on.
3344 @deffn {Scheme Procedure} uname
3345 @deffnx {C Function} scm_uname ()
3346 Return an object with some information about the computer
3347 system the program is running on.
3349 The following procedures accept an object as returned by @code{uname}
3350 and return a selected component (all of which are strings).
3352 @deffn {Scheme Procedure} utsname:sysname un
3353 The name of the operating system.
3355 @deffn {Scheme Procedure} utsname:nodename un
3356 The network name of the computer.
3358 @deffn {Scheme Procedure} utsname:release un
3359 The current release level of the operating system implementation.
3361 @deffn {Scheme Procedure} utsname:version un
3362 The current version level within the release of the operating system.
3364 @deffn {Scheme Procedure} utsname:machine un
3365 A description of the hardware.
3369 @deffn {Scheme Procedure} gethostname
3370 @deffnx {C Function} scm_gethostname ()
3372 Return the host name of the current processor.
3375 @deffn {Scheme Procedure} sethostname name
3376 @deffnx {C Function} scm_sethostname (name)
3377 Set the host name of the current processor to @var{name}. May
3378 only be used by the superuser. The return value is not
3386 @deffn {Scheme Procedure} setlocale category [locale]
3387 @deffnx {C Function} scm_setlocale (category, locale)
3388 Get or set the current locale, used for various internationalizations.
3389 Locales are strings, such as @samp{sv_SE}.
3391 If @var{locale} is given then the locale for the given @var{category}
3392 is set and the new value returned. If @var{locale} is not given then
3393 the current value is returned. @var{category} should be one of the
3394 following values (@pxref{Locale Categories, Categories of Activities
3395 that Locales Affect,, libc, The GNU C Library Reference Manual}):
3400 @defvarx LC_MESSAGES
3401 @defvarx LC_MONETARY
3407 A common usage is @samp{(setlocale LC_ALL "")}, which initializes all
3408 categories based on standard environment variables (@code{LANG} etc).
3409 For full details on categories and locale names @pxref{Locales,,
3410 Locales and Internationalization, libc, The GNU C Library Reference
3413 Note that @code{setlocale} affects locale settings for the whole
3414 process. @xref{i18n Introduction, locale objects and
3415 @code{make-locale}}, for a thread-safe alternative.
3419 @subsection Encryption
3422 Please note that the procedures in this section are not suited for
3423 strong encryption, they are only interfaces to the well-known and
3424 common system library functions of the same name. They are just as good
3425 (or bad) as the underlying functions, so you should refer to your system
3426 documentation before using them (@pxref{crypt,, Encrypting Passwords,
3427 libc, The GNU C Library Reference Manual}).
3429 @deffn {Scheme Procedure} crypt key salt
3430 @deffnx {C Function} scm_crypt (key, salt)
3431 Encrypt @var{key}, with the addition of @var{salt} (both strings),
3432 using the @code{crypt} C library call.
3435 Although @code{getpass} is not an encryption procedure per se, it
3436 appears here because it is often used in combination with @code{crypt}:
3438 @deffn {Scheme Procedure} getpass prompt
3439 @deffnx {C Function} scm_getpass (prompt)
3441 Display @var{prompt} to the standard error output and read
3442 a password from @file{/dev/tty}. If this file is not
3443 accessible, it reads from standard input. The password may be
3444 up to 127 characters in length. Additional characters and the
3445 terminating newline character are discarded. While reading
3446 the password, echoing and the generation of signals by special
3447 characters is disabled.
3452 @c TeX-master: "guile.texi"