realpath(3)                Library Functions Manual                realpath(3)

NAME
       realpath - return the canonicalized absolute pathname

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <limits.h>
       #include <stdlib.h>

       char *realpath(const char *restrict path,
                      char *restrict resolved_path);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       realpath():
           _XOPEN_SOURCE >= 500
               || /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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
       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
       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.  (Before glibc 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 |
       +--------------------------------------------+---------------+---------+
VERSIONS
   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.

STANDARDS
       POSIX.1-2008.

HISTORY
       4.4BSD, POSIX.1-2001, Solaris.

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

       (But see the BUGS section.)

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.

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

Linux man-pages 6.7               2023-10-31                       realpath(3)