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)