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



NAME
       realpath - return the canonicalized absolute pathname

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

DESCRIPTION
       realpath()  expands  all  symbolic links and resolves references to /./, /../ and extra '/' characters in the null-termi-
       nated string named by path to produce a canonicalized absolute pathname.  The resulting pathname is stored as a null-ter-
       minated  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  pathname,  and  returns  a  pointer  to this buffer.  The caller should deallocate 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 indi-
       cate 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.

       POSIX.1-2001  says  that  the  behavior  if  resolved_path is NULL is implementation-defined.  POSIX.1-2008 specifies the
       behavior described in this page.

NOTES
       In 4.4BSD and Solaris the limit on the pathname length is MAXPATHLEN (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 pathname.  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 buffer, 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 fea-
       ture, 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 3.25 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/.



                                                           2009-02-23                                                REALPATH(3)