realpath(3) — Linux manual page


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

NAME         top

       realpath - return the canonicalized absolute pathname

SYNOPSIS         top

       #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

DESCRIPTION         top

       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).

RETURN VALUE         top

       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.

ERRORS         top

       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

              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.

ATTRIBUTES         top

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

       │Interface  Attribute     Value   │
       │realpath() │ Thread safety │ MT-Safe │

CONFORMING TO         top

       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         top

       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.

BUGS         top

       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.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.09 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

                                 2017-09-15                      REALPATH(3)

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