realpath - return the canonicalized absolute pathname
SYNOPSIS
#include <limits.h>
#include <stdlib.h>
char *realpath(const char *path, char *resolved_path);
DESCRIPTION
realpath expands all symbolic links and resolves refer
ences to '/./', '/../' and extra '/' characters in the
null terminated string named by path and stores the canon
icalized 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, it 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 indicate the error.
ERRORS
EACCES Read or search permission was denied for a compo
nent of the path prefix.
EINVAL Either path or resolved_path is NULL. (In libc5
this would just cause a segfault.)
EIO An I/O error occurred while reading from the file
system.
ELOOP Too many symbolic links were encountered in trans
lating the pathname.
ENAMETOOLONG
A component of a path name exceeded NAME_MAX char
acters, or an entire path name exceeded PATH_MAX
characters.
ENOENT The named file does not exist.
ENOTDIR
A component of the path prefix is not a directory.
BUGS
The libc4 and libc5 implementation contains a buffer over
flow (fixed in libc-5.4.13). Thus, suid programs like
mount need a private version.
The length of the output buffer should have been an
that the result of pathconf() may be huge and unsuitable
for mallocing memory.
HISTORY
The realpath function first appeared in BSD 4.4, con
tributed by Jan-Simon Pendry. In Linux this function
appears in libc 4.5.21.
CONFORMING TO
In BSD 4.4 and Solaris the limit on the pathname length is
MAXPATHLEN (found in <sys/param.h>). The 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
The BSD 4.4, Linux and SUSv2 versions always return an
absolute path name. Solaris may return a relative path
name 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 ALSO
readlink(2), getcwd(3), pathconf(3), sysconf(3)
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