REALPATH(3) Linux Programmer's Manual REALPATH(3)
realpath - return the canonicalized absolute pathname
char *realpath(const char *path, char *resolved_path);
realpath expands all symbolic links and resolves references to '/./', '/../' and extra '/'
characters in the null terminated string named by path and stores the canonicalized abso-
lute pathname in the buffer of size PATH_MAX named by resolved_path. The resulting path
will have no symbolic link, '/./' or '/../' components.
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 unde-
fined. The global variable 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.)
EIO An I/O error occurred while reading from the file system.
ELOOP Too many symbolic links were encountered in translating the pathname.
A component of a path name exceeded NAME_MAX characters, or an entire path name
exceeded PATH_MAX characters.
ENOENT The named file does not exist.
A component of the path prefix is not a directory.
The libc4 and libc5 implementation contains a buffer overflow (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 additional parameter, especially since
pathconf(3) warns that the result of pathconf() may be huge and unsuitable for mallocing
The realpath function first appeared in BSD 4.4, contributed by Jan-Simon Pendry. In
Linux this function appears in libc 4.5.21.
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 pro-
vided by the pathconf() function. A typical source fragment would be
path_max = PATH_MAX;
path_max = pathconf (path, _PC_PATH_MAX);
if (path_max <= 0)
path_max = 4096;
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.
readlink(2), getcwd(3), pathconf(3), sysconf(3)