realpath - return the canonicalized absolute pathname


   #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)):

       _XOPEN_SOURCE >= 500
           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE


   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
   pathname 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
   pathname, and returns a pointer to  this  buffer.   The  caller  should
   deallocate this buffer using free(3).


   If   there   is   no   error,  realpath()  returns  a  pointer  to  the

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


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

   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 filesystem.

   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.

   ENOMEM Out of memory.

          A component of the path prefix is not a directory.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   Interface   Attribute      Value   
   realpath()  Thread safety  MT-Safe 


   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.


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

   (But see the BUGS section.)

   GNU extensions
   If the call fails with either EACCES or ENOENT and resolved_path is not
   NULL, then the prefix of path that is not readable or does not exist is
   returned in resolved_path.


   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  feature,  not  standardized  in
   POSIX.1-2001, but standardized  in  POSIX.1-2008,  allows  this  design
   problem to be avoided.


   realpath(1),    readlink(2),    canonicalize_file_name(3),   getcwd(3),
   pathconf(3), sysconf(3)


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at

                              2016-10-08                       REALPATH(3)


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