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Diffstat (limited to 'man/man3/getcwd.3')
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diff --git a/man/man3/getcwd.3 b/man/man3/getcwd.3 new file mode 100644 index 000000000..6ba1e3280 --- /dev/null +++ b/man/man3/getcwd.3 @@ -0,0 +1,311 @@ +'\" t +.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" Modified Wed Jul 21 22:35:42 1993 by Rik Faith (faith@cs.unc.edu) +.\" Modified 18 Mar 1996 by Martin Schulze (joey@infodrom.north.de): +.\" Corrected description of getwd(). +.\" Modified Sat Aug 21 12:32:12 MET 1999 by aeb - applied fix by aj +.\" Modified Mon Dec 11 13:32:51 MET 2000 by aeb +.\" Modified Thu Apr 22 03:49:15 CEST 2002 by Roger Luethi <rl@hellgate.ch> +.\" +.TH getcwd 3 (date) "Linux man-pages (unreleased)" +.SH NAME +getcwd, getwd, get_current_dir_name \- get current working directory +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <unistd.h> +.P +.BI "char *getcwd(char " buf [. size "], size_t " size ); +.B "char *get_current_dir_name(void);" +.P +.BI "[[deprecated]] char *getwd(char " buf [PATH_MAX]); +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.BR get_current_dir_name (): +.nf + _GNU_SOURCE +.fi +.P +.BR getwd (): +.nf + Since glibc 2.12: + (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L) + || /* glibc >= 2.19: */ _DEFAULT_SOURCE + || /* glibc <= 2.19: */ _BSD_SOURCE + Before glibc 2.12: + _BSD_SOURCE || _XOPEN_SOURCE >= 500 +.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED +.fi +.SH DESCRIPTION +These functions return a null-terminated string containing an +absolute pathname that is the current working directory of +the calling process. +The pathname is returned as the function result and via the argument +.IR buf , +if present. +.P +The +.BR getcwd () +function copies an absolute pathname of the current working directory +to the array pointed to by +.IR buf , +which is of length +.IR size . +.P +If the length of the absolute pathname of the current working directory, +including the terminating null byte, exceeds +.I size +bytes, NULL is returned, and +.I errno +is set to +.BR ERANGE ; +an application should check for this error, and allocate a larger +buffer if necessary. +.P +As an extension to the POSIX.1-2001 standard, glibc's +.BR getcwd () +allocates the buffer dynamically using +.BR malloc (3) +if +.I buf +is NULL. +In this case, the allocated buffer has the length +.I size +unless +.I size +is zero, when +.I buf +is allocated as big as necessary. +The caller should +.BR free (3) +the returned buffer. +.P +.BR get_current_dir_name () +will +.BR malloc (3) +an array big enough to hold the absolute pathname of +the current working directory. +If the environment +variable +.B PWD +is set, and its value is correct, then that value will be returned. +The caller should +.BR free (3) +the returned buffer. +.P +.BR getwd () +does not +.BR malloc (3) +any memory. +The +.I buf +argument should be a pointer to an array at least +.B PATH_MAX +bytes long. +If the length of the absolute pathname of the current working directory, +including the terminating null byte, exceeds +.B PATH_MAX +bytes, NULL is returned, and +.I errno +is set to +.BR ENAMETOOLONG . +(Note that on some systems, +.B PATH_MAX +may not be a compile-time constant; +furthermore, its value may depend on the filesystem, see +.BR pathconf (3).) +For portability and security reasons, use of +.BR getwd () +is deprecated. +.SH RETURN VALUE +On success, these functions return a pointer to a string containing +the pathname of the current working directory. +In the case of +.BR getcwd () +and +.BR getwd () +this is the same value as +.IR buf . +.P +On failure, these functions return NULL, and +.I errno +is set to indicate the error. +The contents of the array pointed to by +.I buf +are undefined on error. +.SH ERRORS +.TP +.B EACCES +Permission to read or search a component of the filename was denied. +.TP +.B EFAULT +.I buf +points to a bad address. +.TP +.B EINVAL +The +.I size +argument is zero and +.I buf +is not a null pointer. +.TP +.B EINVAL +.BR getwd (): +.I buf +is NULL. +.TP +.B ENAMETOOLONG +.BR getwd (): +The size of the null-terminated absolute pathname string exceeds +.B PATH_MAX +bytes. +.TP +.B ENOENT +The current working directory has been unlinked. +.TP +.B ENOMEM +Out of memory. +.TP +.B ERANGE +The +.I size +argument is less than the length of the absolute pathname of the +working directory, including the terminating null byte. +You need to allocate a bigger array and try again. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR getcwd (), +.BR getwd () +T} Thread safety MT-Safe +T{ +.na +.nh +.BR get_current_dir_name () +T} Thread safety MT-Safe env +.TE +.SH VERSIONS +POSIX.1-2001 leaves the behavior of +.BR getcwd () +unspecified if +.I buf +is NULL. +.P +POSIX.1-2001 +does not define any errors for +.BR getwd (). +.SH VERSIONS +.SS C library/kernel differences +On Linux, the kernel provides a +.BR getcwd () +system call, which the functions described in this page will use if possible. +The system call takes the same arguments as the library function +of the same name, but is limited to returning at most +.B PATH_MAX +bytes. +(Before Linux 3.12, +.\" commit 3272c544da48f8915a0e34189182aed029bd0f2b +the limit on the size of the returned pathname was the system page size. +On many architectures, +.B PATH_MAX +and the system page size are both 4096 bytes, +but a few architectures have a larger page size.) +If the length of the pathname of the current working directory +exceeds this limit, then the system call fails with the error +.BR ENAMETOOLONG . +In this case, the library functions fall back to +a (slower) alternative implementation that returns the full pathname. +.P +Following a change in Linux 2.6.36, +.\" commit 8df9d1a4142311c084ffeeacb67cd34d190eff74 +the pathname returned by the +.BR getcwd () +system call will be prefixed with the string "(unreachable)" +if the current directory is not below the root directory of the current +process (e.g., because the process set a new filesystem root using +.BR chroot (2) +without changing its current directory into the new root). +Such behavior can also be caused by an unprivileged user by changing +the current directory into another mount namespace. +When dealing with pathname from untrusted sources, callers of the +functions described in this page +should consider checking whether the returned pathname starts +with '/' or '(' to avoid misinterpreting an unreachable path +as a relative pathname. +.SH STANDARDS +.TP +.BR getcwd () +POSIX.1-2008. +.TP +.BR get_current_dir_name () +GNU. +.TP +.BR getwd () +None. +.SH HISTORY +.TP +.BR getcwd () +POSIX.1-2001. +.TP +.BR getwd () +POSIX.1-2001, but marked LEGACY. +Removed in POSIX.1-2008. +Use +.BR getcwd () +instead. +.P +Under Linux, these functions make use of the +.BR getcwd () +system call (available since Linux 2.1.92). +On older systems they would query +.IR /proc/self/cwd . +If both system call and proc filesystem are missing, a +generic implementation is called. +Only in that case can +these calls fail under Linux with +.BR EACCES . +.SH NOTES +These functions are often used to save the location of the current working +directory for the purpose of returning to it later. +Opening the current +directory (".") and calling +.BR fchdir (2) +to return is usually a faster and more reliable alternative when sufficiently +many file descriptors are available, especially on platforms other than Linux. +.SH BUGS +Since the Linux 2.6.36 change that added "(unreachable)" in the +circumstances described above, the glibc implementation of +.BR getcwd () +has failed to conform to POSIX and returned a relative pathname when the API +contract requires an absolute pathname. +With glibc 2.27 onwards this is corrected; +calling +.BR getcwd () +from such a pathname will now result in failure with +.BR ENOENT . +.SH SEE ALSO +.BR pwd (1), +.BR chdir (2), +.BR fchdir (2), +.BR open (2), +.BR unlink (2), +.BR free (3), +.BR malloc (3) |