realpath(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

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 *restrict path,
                      char *restrict resolved_path);

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

       realpath():
           _XOPEN_SOURCE >= 500
               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 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
       resolved_path.

       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 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         top

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

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │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;
           #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         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 5.13 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
       https://www.kernel.org/doc/man-pages/.

                               2021-03-22                    REALPATH(3)

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