REALPATH(3) Linux Programmer's Manual REALPATH(3)NAMErealpath - return the canonicalized absolute pathname
SYNOPSIS
#include <limits.h>
#include <stdlib.h>
char *realpath(const char *path, char *resolved_path);
DESCRIPTIONrealpath() expands all symbolic links and resolves references to '/./',
'/../' and extra '/' characters in the null terminated string named by
path and stores the canonicalized absolute pathname in the buffer of
size PATH_MAX named by resolved_path. The resulting path will have no
symbolic link, '/./' or '/../' components.
RETURN VALUE
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. The global variable errno is set to indi‐
cate the error.
ERRORS
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.
NOTES
The glibc implementation of realpath() provides a non-standard exten‐
sion. If resolved_path is specified as NULL, then realpath() uses mal‐
loc(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).
BUGS
Avoid using this function. It is broken by design since (unless using
the non-standard resolved_path == NULL feature) it is impossible to
determine a suitable size for the output buffer, resolved_path.
According to POSIX a buffer of size PATH_MAX suffices, but PATH_MAX
need not be a defined constant, and may have to be obtained using path‐
conf(). And asking pathconf() does not really help, since on the one
hand POSIX warns that the result of pathconf() may be huge and unsuit‐
able for mallocing memory. And on the other hand pathconf() may return
-1 to signify that PATH_MAX is not bounded.
The libc4 and libc5 implementation contains a buffer overflow (fixed in
libc-5.4.13). Thus, set-user-ID programs like mount need a private
version.
HISTORY
The realpath() function first appeared in 4.4BSD, contributed by Jan-
Simon Pendry. In Linux this function appears in libc 4.5.21.
CONFORMING TO
4.4BSD, POSIX.1-2001.
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() 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 path‐
name. 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.
SEE ALSOreadlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3),
sysconf(3)
2004-12-14 REALPATH(3)
