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

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 NULL, 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 filesystem.

     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.

     ENOMEM Out of memory.

     ENOTDIR
            A component of the path prefix is not a directory.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).

     +-----------+---------------+---------+
     |Interface  | Attribute     | Value   |
     +-----------+---------------+---------+
     |realpath() | Thread safety | MT-Safe |
     +-----------+---------------+---------+

CONFORMING TO

     4.4BSD, POSIX.1-2001.

     POSIX.1-2001 says that the behavior if resolved_path is NULL is  imple-
     mentation-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.)

 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.

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