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       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.

              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.

              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


       The  realpath  function  first  appeared  in BSD 4.4, contributed by Jan-Simon 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;
                path_max = pathconf (path, _PC_PATH_MAX);
                if (path_max <= 0)
                  path_max = 4096;

       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)

                                          24 August 1999                              REALPATH(3)