realpath - return the canonicalized absolute pathname
#include <limits.h>
#include <stdlib.h>
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 absolute 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 undefined. 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.
ENAMETOOLONG [Toc] [Back]
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.
ENOTDIR [Toc] [Back]
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 memory.
The realpath function first appeared in BSD 4.4, contributed by JanSimon
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 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.
readlink(2), getcwd(3), pathconf(3), sysconf(3)
1999-08-24 REALPATH(3)
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