REALPATH
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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 aq/aq
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.
(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 implementation-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.
SEE ALSO
realpath(1),
readlink(2),
canonicalize_file_name(3),
getcwd(3),
pathconf(3),
sysconf(3)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- GNU extensions
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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