realpath


SYNOPSIS
       #include <limits.h>
       #include <stdlib.h>

       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 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION
       realpath() expands all symbolic links and resolves references  to  /./,
       /../  and  extra  '/' characters in the null-terminated string named by
       path to produce a canonicalized absolute pathname.  The resulting path-
       name is stored as a null-terminated string, up to a maximum of PATH_MAX
       bytes, in the buffer pointed to by resolved_path.  The  resulting  path
       will have no symbolic link, /./ or /../ components.

       If  resolved_path  is specified as NULL, then realpath() uses malloc(3)
       to allocate a buffer of up to PATH_MAX bytes to hold the resolved path-
       name,  and returns a pointer to this buffer.  The caller should deallo-
       cate this buffer using free(3).

RETURN VALUE
       If  there  is  no  error,  realpath()  returns   a   pointer   to   the
       resolved_path.

       Otherwise  it  returns  a  NULL  pointer, and the contents of the array
       resolved_path are undefined, and errno is set to indicate the error.

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

       EINVAL path is NULL.  (In glibc versions before 2.3, this error is also
              returned if resolved_path is NULL.)

       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.

       (found  in  <sys/param.h>).  SUSv2 prescribes PATH_MAX and 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 path-
       name.  Solaris may return a relative pathname 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.

BUGS
       The POSIX.1-2001 standard version of this function is broken by design,
       since it is impossible to determine a suitable size for the output buf-
       fer,  resolved_path.   According  to  POSIX.1-2001  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  resolved_path == NULL  feature,  not  standardized   in
       POSIX.1-2001,  but  standardized  in  POSIX.1-2008,  allows this design
       problem to be avoided.

       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
       version.

SEE ALSO
       readlink(2),   canonicalize_file_name(3),    getcwd(3),    pathconf(3),
       sysconf(3)

COLOPHON
       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



                                  2011-09-10                       REALPATH(3)
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