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REALPATH(3) Linux Programmer's Manual REALPATH(3)
realpath - return the canonicalized absolute pathname
#include <limits.h>
#include <stdlib.h>
char *realpath(const char *path, char *resolved_path);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
realpath():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
realpath() expands all symbolic links and resolves references to /./, /../ and
extra '/' characters in the null-terminated string named by path to produce a
canonicalized absolute pathname. The resulting pathname is stored as a null-
terminated string, up to a maximum of PATH_MAX bytes, in the buffer pointed to
by resolved_path. The resulting path will have no symbolic link, /./ or /../
components.
If resolved_path is specified as NULL, then realpath() uses malloc(3) to
allocate a buffer of up to PATH_MAX bytes to hold the resolved pathname, and
returns a pointer to this buffer. The caller should deallocate this buffer
using free(3).
If there is no error, realpath() returns a pointer to the resolved_path.
Otherwise it returns a NULL pointer, and the contents of the array
resolved_path are undefined, and errno is set to indicate the error.
EACCES Read or search permission was denied for a component of the path
prefix.
EINVAL Either path or resolved_path is NULL. (In libc5 this would just cause
a segfault.) But, see NOTES below.
EIO An I/O error occurred while reading from the file system.
ELOOP Too many symbolic links were encountered in translating the pathname.
ENAMETOOLONG
A component of a pathname exceeded NAME_MAX characters, or an entire
pathname exceeded PATH_MAX characters.
ENOENT The named file does not exist.
ENOTDIR
A component of the path prefix is not a directory.
On Linux this function appeared in libc 4.5.21.
4.4BSD, POSIX.1-2001.
POSIX.1-2001 says that the behavior if resolved_path is NULL is
implementation-defined. POSIX.1-2008 specifies the behavior described in this
page.
In 4.4BSD and Solaris the limit on the pathname length is MAXPATHLEN (found in
<sys/param.h>). SUSv2 prescribes PATH_MAX and NAME_MAX, as found in
<limits.h> or provided by the pathconf(3) function. A typical source fragment
would be
#ifdef PATH_MAX
path_max = PATH_MAX;
#else
path_max = pathconf(path, _PC_PATH_MAX);
if (path_max <= 0)
path_max = 4096;
#endif
(But see the BUGS section.)
The 4.4BSD, Linux and SUSv2 versions always return an absolute pathname.
Solaris may return a relative pathname when the path argument is relative.
The prototype of realpath() is given in <unistd.h> in libc4 and libc5, but in
<stdlib.h> everywhere else.
The POSIX.1-2001 standard version of this function is broken by design, since
it is impossible to determine a suitable size for the output buffer,
resolved_path. According to POSIX.1-2001 a buffer of size PATH_MAX suffices,
but PATH_MAX need not be a defined constant, and may have to be obtained using
pathconf(3). And asking pathconf(3) does not really help, since, on the one
hand POSIX warns that the result of pathconf(3) may be huge and unsuitable for
mallocing memory, and on the other hand pathconf(3) may return -1 to signify
that PATH_MAX is not bounded. The resolved_path == NULL feature, not
standardized in POSIX.1-2001, but standardized in POSIX.1-2008, allows this
design problem to be avoided.
The libc4 and libc5 implementation contains a buffer overflow (fixed in
libc-5.4.13). Thus, set-user-ID programs like mount(8) need a private
version.
readlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3), sysconf(3)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
2010-09-20 REALPATH(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface