NAME
realpath - return the canonicalized absolute pathname
SYNOPSIS
#include <limits.h>
#include <stdlib.h>
I char *realpath(const char * path , char * resolved_path );
DESCRIPTION
R realpath ()
expands all symbolic links and resolves references
to
R '/./' , '/../'
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
R resolved_path .
The resulting path will have no symbolic link,
'/./'
or
'/../'
components.
RETURN VALUE
If there is no error,
R realpath ()
returns a pointer to the
R 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 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.
VERSIONS
On Linux this function appeared 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
R PATH_MAX
and
R 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
R realpath ()
is given in <unistd.h> in libc4 and libc5,
but in <stdlib.h> everywhere else.
NOTES
The glibc implementation of
R realpath ()
provides a non-standard extension.
If
resolved_path
is specified as NULL, then
R 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).
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,
R 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
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 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.
SEE ALSO
ČLÁNKY DO MAILU