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REALPATH(3)                Linux Programmer's Manual               REALPATH(3)

       realpath - return the canonicalized absolute pathname

       #include <&lt;limits.h>&gt;
       #include <&lt;stdlib.h>&gt;

       char *realpath(const char *path, char *resolved_path);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       realpath(): _BSD_SOURCE || _XOPEN_SOURCE >= 500

       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,  realpath()  returns  a  pointer  to  the

       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.

       EACCES Read or search permission was denied for a component of the path

       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

              A  component  of  a pathname exceeded NAME_MAX characters, or an
              entire pathname exceeded PATH_MAX characters.

       ENOENT The named file does not exist.

              A component of the path prefix is not a directory.

       On Linux this function appeared in libc 4.5.21.

       4.4BSD, POSIX.1-2001.

       In 4.4BSD and Solaris the limit on the pathname  length  is  MAXPATHLEN
       (found  in  &lt;sys/param.h&gt;).  SUSv2 prescribes PATH_MAX and NAME_MAX, as
       found in &lt;limits.h&gt; or provided by the pathconf(3) function.  A typical
       source fragment would be

           #ifdef PATH_MAX
             path_max = PATH_MAX;
             path_max = pathconf(path, _PC_PATH_MAX);
             if (path_max <= 0)
               path_max = 4096;

       (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 &lt;unistd.h&gt; in libc4
       and libc5, but in &lt;stdlib.h&gt; everywhere else.

       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).

       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(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 unsuit-
       able  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(8) need a private

       readlink(2),   canonicalize_file_name(3),    getcwd(3),    pathconf(3),

       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

                                  2007-07-26                       REALPATH(3)