getcwd (2)
Leading comments
Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this on...
NAME
getcwd, getwd, get_current_dir_name - get current working directorySYNOPSIS
#include <unistd.h> char *getcwd(char *buf, size_t size); char *getwd(char *buf); char *get_current_dir_name(void);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
get_current_dir_name():
- _GNU_SOURCE
getwd():
-
- Since glibc 2.12:
-
_BSD_SOURCE || (_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) && !(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700) - Before glibc 2.12: _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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 buf, if present.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 chroot(2) without changing its current directory into the new root), then, since Linux 2.6.36, the returned path will be prefixed with the string "(unreachable)". Such behavior can also be caused by an unprivileged user by changing the current directory into another mount namespace. When dealing with paths from untrusted sources, callers of these functions should consider checking whether the returned path starts with '/' or '(' to avoid misinterpreting an unreachable path as a relative path.
The getcwd() function copies an absolute pathname of the current working directory to the array pointed to by buf, which is of length size.
If the length of the absolute pathname of the current working directory, including the terminating null byte, exceeds size bytes, NULL is returned, and errno is set to ERANGE; an application should check for this error, and allocate a larger buffer if necessary.
As an extension to the POSIX.1-2001 standard, glibc's
getcwd()
allocates the buffer dynamically using
malloc(3)
if
buf
is NULL.
In this case, the allocated buffer has the length
size
unless
size
is zero, when
buf
is allocated as big as necessary.
The caller should
free(3)
the returned buffer.
get_current_dir_name()
will
malloc(3)
an array big enough to hold the absolute pathname of
the current working directory.
If the environment
variable
PWD
is set, and its value is correct, then that value will be returned.
The caller should
free(3)
the returned buffer.
getwd()
does not
malloc(3)
any memory.
The
buf
argument should be a pointer to an array at least
PATH_MAX
bytes long.
If the length of the absolute pathname of the current working directory,
including the terminating null byte, exceeds
PATH_MAX
bytes, NULL is returned, and
errno
is set to
ENAMETOOLONG.
(Note that on some systems,
PATH_MAX
may not be a compile-time constant;
furthermore, its value may depend on the filesystem, see
pathconf(3).)
For portability and security reasons, use of
getwd()
is deprecated.
RETURN VALUE
On success, these functions return a pointer to a string containing the pathname of the current working directory. In the case getcwd() and getwd() this is the same value as buf.On failure, these functions return NULL, and errno is set to indicate the error. The contents of the array pointed to by buf are undefined on error.
ERRORS
- EACCES
- Permission to read or search a component of the filename was denied.
- EFAULT
- buf points to a bad address.
- EINVAL
- The size argument is zero and buf is not a null pointer.
- EINVAL
- getwd(): buf is NULL.
- ENAMETOOLONG
- getwd(): The size of the null-terminated absolute pathname string exceeds PATH_MAX bytes.
- ENOMEM
- Out of memory.
- ENOENT
- The current working directory has been unlinked.
- ERANGE
- The 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| getcwd(), getwd() | Thread safety | MT-Safe |
| get_current_dir_name() | Thread safety | MT-Safe env |
CONFORMING TO
getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001 leaves the behavior of getcwd() unspecified if buf is NULL.getwd() is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008 removes the specification of getwd(). Use getcwd() instead. POSIX.1-2001 does not define any errors for getwd().
get_current_dir_name() is a GNU extension.
NOTES
Under Linux, the function getcwd() is a system call (since 2.1.92). On older systems it would query /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 EACCES.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 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.