[thirdparty/man-pages.git] / man3 / realpath.3

.\" Copyright (C) 1999 Andries Brouwer (aeb@cwi.nl)
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Rewritten old page, 990824, aeb@cwi.nl
.\" 2004-12-14, mtk, added discussion of resolved_path == NULL
.\"
.TH REALPATH 3  2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
realpath \- return the canonicalized absolute pathname
.SH SYNOPSIS
.nf
.B #include <limits.h>
.B #include <stdlib.h>
.PP
.BI "char *realpath(const char *" path ", char *" resolved_path );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.BR realpath ():
.ad l
.RS 4
_XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
    || /* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.RE
.ad
.SH DESCRIPTION
.BR realpath ()
expands all symbolic links and resolves references
to
.IR "/./" ", " "/../"
and extra \(aq/\(aq
characters in the null-terminated string named by
.I path
to produce a canonicalized absolute pathname.
The resulting pathname is stored as a null-terminated string,
up to a maximum of
.B PATH_MAX
bytes,
in the buffer pointed to by
.IR resolved_path .
The resulting path will have no symbolic link,
.I "/./"
or
.I "/../"
components.
.PP
If
.I resolved_path
is specified as NULL, then
.BR realpath ()
uses
.BR malloc (3)
to allocate a buffer of up to
.B PATH_MAX
bytes to hold the resolved pathname,
and returns a pointer to this buffer.
The caller should deallocate this buffer using
.BR free (3).
.\" Even if we use resolved_path == NULL, then realpath() will still
.\" return ENAMETOOLONG if the resolved pathname would exceed PATH_MAX
.\" bytes -- MTK, Dec 04
.\" .SH HISTORY
.\" The
.\" .BR realpath ()
.\" function first appeared in 4.4BSD, contributed by Jan-Simon Pendry.
.SH RETURN VALUE
If there is no error,
.BR realpath ()
returns a pointer to the
.IR resolved_path .
.PP
Otherwise, it returns NULL, the contents
of the array
.I resolved_path
are undefined, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EACCES
Read or search permission was denied for a component of the path prefix.
.TP
.B EINVAL
.I path
is NULL.
.\" (In libc5 this would just cause a segfault.)
(In glibc versions before 2.3,
this error is also returned if
.IR resolved_path
is NULL.)
.TP
.B EIO
An I/O error occurred while reading from the filesystem.
.TP
.B ELOOP
Too many symbolic links were encountered in translating the pathname.
.TP
.B ENAMETOOLONG
A component of a pathname exceeded
.B NAME_MAX
characters, or an entire pathname exceeded
.B PATH_MAX
characters.
.TP
.B ENOENT
The named file does not exist.
.TP
.B ENOMEM
Out of memory.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR realpath ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
4.4BSD, POSIX.1-2001.
.PP
POSIX.1-2001 says that the behavior if
.I resolved_path
is NULL is implementation-defined.
POSIX.1-2008 specifies the behavior described in this page.
.SH NOTES
In 4.4BSD and Solaris, the limit on the pathname length is
.B MAXPATHLEN
(found in \fI<sys/param.h>\fP).
SUSv2 prescribes
.B PATH_MAX
and
.BR NAME_MAX ,
as found in \fI<limits.h>\fP or provided by the
.BR pathconf (3)
function.
A typical source fragment would be
.PP
.in +4n
.EX
#ifdef PATH_MAX
  path_max = PATH_MAX;
#else
  path_max = pathconf(path, _PC_PATH_MAX);
  if (path_max <= 0)
    path_max = 4096;
#endif
.EE
.in
.PP
(But see the BUGS section.)
.PP
.\"     2012-05-05, According to Casper Dik, the statement about
.\"     Solaris was not true at least as far back as 1997, and
.\"     may never have been true.
.\"
.\" The 4.4BSD, Linux and SUSv2 versions always return an absolute
.\" pathname.
.\" Solaris may return a relative pathname when the
.\" .I path
.\" argument is relative.
.\" The prototype of
.\" .BR realpath ()
.\" is given in \fI<unistd.h>\fP in libc4 and libc5,
.\" but in \fI<stdlib.h>\fP everywhere else.
.SS GNU extensions
If the call fails with either
.BR EACCES
or
.BR ENOENT
and
.I resolved_path
is not NULL, then the prefix of
.I path
that is not readable or does not exist is returned in
.IR resolved_path .
.SH 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,
.IR resolved_path .
According to POSIX.1-2001 a buffer of size
.B PATH_MAX
suffices, but
.B PATH_MAX
need not be a defined constant, and may have to be obtained using
.BR pathconf (3).
And asking
.BR pathconf (3)
does not really help, since, on the one hand POSIX warns that
the result of
.BR pathconf (3)
may be huge and unsuitable for mallocing memory,
and on the other hand
.BR pathconf (3)
may return \-1 to signify that
.B PATH_MAX
is not bounded.
The
.I "resolved_path\ ==\ NULL"
feature, not standardized in POSIX.1-2001,
but standardized in POSIX.1-2008, allows this design problem to be avoided.
.\" .LP
.\" The libc4 and libc5 implementation contained a buffer overflow
.\" (fixed in libc-5.4.13).
.\" Thus, set-user-ID programs like
.\" .BR mount (8)
.\" needed a private version.
.SH SEE ALSO
.BR realpath (1),
.BR readlink (2),
.BR canonicalize_file_name (3),
.BR getcwd (3),
.BR pathconf (3),
.BR sysconf (3)
Commit	Line	Data
	1	.\" Copyright (C) 1999 Andries Brouwer (aeb@cwi.nl)
	2	.\"
	3	.\" %%%LICENSE_START(VERBATIM)
	4	.\" Permission is granted to make and distribute verbatim copies of this
	5	.\" manual provided the copyright notice and this permission notice are
	6	.\" preserved on all copies.
	7	.\"
	8	.\" Permission is granted to copy and distribute modified versions of this
	9	.\" manual under the conditions for verbatim copying, provided that the
	10	.\" entire resulting derived work is distributed under the terms of a
	11	.\" permission notice identical to this one.
	12	.\"
	13	.\" Since the Linux kernel and libraries are constantly changing, this
	14	.\" manual page may be incorrect or out-of-date. The author(s) assume no
	15	.\" responsibility for errors or omissions, or for damages resulting from
	16	.\" the use of the information contained herein. The author(s) may not
	17	.\" have taken the same level of care in the production of this manual,
	18	.\" which is licensed free of charge, as they might when working
	19	.\" professionally.
	20	.\"
	21	.\" Formatted or processed versions of this manual, if unaccompanied by
	22	.\" the source, must acknowledge the copyright and authors of this work.
	23	.\" %%%LICENSE_END
	24	.\"
	25	.\" Rewritten old page, 990824, aeb@cwi.nl
	26	.\" 2004-12-14, mtk, added discussion of resolved_path == NULL
	27	.\"
	28	.TH REALPATH 3 2017-09-15 "" "Linux Programmer's Manual"
	29	.SH NAME
	30	realpath \- return the canonicalized absolute pathname
	31	.SH SYNOPSIS
	32	.nf
	33	.B #include <limits.h>
	34	.B #include <stdlib.h>
	35	.PP
	36	.BI "char realpath(const char " path ", char *" resolved_path );
	37	.fi
	38	.PP
	39	.in -4n
	40	Feature Test Macro Requirements for glibc (see
	41	.BR feature_test_macros (7)):
	42	.in
	43	.PP
	44	.BR realpath ():
	45	.ad l
	46	.RS 4
	47	_XOPEN_SOURCE\ >=\ 500
	48	.\" \|\| _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
	49	\|\| /* Glibc since 2.19: */ _DEFAULT_SOURCE
	50	\|\| /* Glibc versions <= 2.19: */ _BSD_SOURCE
	51	.RE
	52	.ad
	53	.SH DESCRIPTION
	54	.BR realpath ()
	55	expands all symbolic links and resolves references
	56	to
	57	.IR "/./" ", " "/../"
	58	and extra \(aq/\(aq
	59	characters in the null-terminated string named by
	60	.I path
	61	to produce a canonicalized absolute pathname.
	62	The resulting pathname is stored as a null-terminated string,
	63	up to a maximum of
	64	.B PATH_MAX
	65	bytes,
	66	in the buffer pointed to by
	67	.IR resolved_path .
	68	The resulting path will have no symbolic link,
	69	.I "/./"
	70	or
	71	.I "/../"
	72	components.
	73	.PP
	74	If
	75	.I resolved_path
	76	is specified as NULL, then
	77	.BR realpath ()
	78	uses
	79	.BR malloc (3)
	80	to allocate a buffer of up to
	81	.B PATH_MAX
	82	bytes to hold the resolved pathname,
	83	and returns a pointer to this buffer.
	84	The caller should deallocate this buffer using
	85	.BR free (3).
	86	.\" Even if we use resolved_path == NULL, then realpath() will still
	87	.\" return ENAMETOOLONG if the resolved pathname would exceed PATH_MAX
	88	.\" bytes -- MTK, Dec 04
	89	.\" .SH HISTORY
	90	.\" The
	91	.\" .BR realpath ()
	92	.\" function first appeared in 4.4BSD, contributed by Jan-Simon Pendry.
	93	.SH RETURN VALUE
	94	If there is no error,
	95	.BR realpath ()
	96	returns a pointer to the
	97	.IR resolved_path .
	98	.PP
	99	Otherwise, it returns NULL, the contents
	100	of the array
	101	.I resolved_path
	102	are undefined, and
	103	.I errno
	104	is set to indicate the error.
	105	.SH ERRORS
	106	.TP
	107	.B EACCES
	108	Read or search permission was denied for a component of the path prefix.
	109	.TP
	110	.B EINVAL
	111	.I path
	112	is NULL.
	113	.\" (In libc5 this would just cause a segfault.)
	114	(In glibc versions before 2.3,
	115	this error is also returned if
	116	.IR resolved_path
	117	is NULL.)
	118	.TP
	119	.B EIO
	120	An I/O error occurred while reading from the filesystem.
	121	.TP
	122	.B ELOOP
	123	Too many symbolic links were encountered in translating the pathname.
	124	.TP
	125	.B ENAMETOOLONG
	126	A component of a pathname exceeded
	127	.B NAME_MAX
	128	characters, or an entire pathname exceeded
	129	.B PATH_MAX
	130	characters.
	131	.TP
	132	.B ENOENT
	133	The named file does not exist.
	134	.TP
	135	.B ENOMEM
	136	Out of memory.
	137	.TP
	138	.B ENOTDIR
	139	A component of the path prefix is not a directory.
	140	.SH ATTRIBUTES
	141	For an explanation of the terms used in this section, see
	142	.BR attributes (7).
	143	.TS
	144	allbox;
	145	lb lb lb
	146	l l l.
	147	Interface Attribute Value
	148	T{
	149	.BR realpath ()
	150	T} Thread safety MT-Safe
	151	.TE
	152	.SH CONFORMING TO
	153	4.4BSD, POSIX.1-2001.
	154	.PP
	155	POSIX.1-2001 says that the behavior if
	156	.I resolved_path
	157	is NULL is implementation-defined.
	158	POSIX.1-2008 specifies the behavior described in this page.
	159	.SH NOTES
	160	In 4.4BSD and Solaris, the limit on the pathname length is
	161	.B MAXPATHLEN
	162	(found in \fI<sys/param.h>\fP).
	163	SUSv2 prescribes
	164	.B PATH_MAX
	165	and
	166	.BR NAME_MAX ,
	167	as found in \fI<limits.h>\fP or provided by the
	168	.BR pathconf (3)
	169	function.
	170	A typical source fragment would be
	171	.PP
	172	.in +4n
	173	.EX
	174	#ifdef PATH_MAX
	175	path_max = PATH_MAX;
	176	#else
	177	path_max = pathconf(path, _PC_PATH_MAX);
	178	if (path_max <= 0)
	179	path_max = 4096;
	180	#endif
	181	.EE
	182	.in
	183	.PP
	184	(But see the BUGS section.)
	185	.PP
	186	.\" 2012-05-05, According to Casper Dik, the statement about
	187	.\" Solaris was not true at least as far back as 1997, and
	188	.\" may never have been true.
	189	.\"
	190	.\" The 4.4BSD, Linux and SUSv2 versions always return an absolute
	191	.\" pathname.
	192	.\" Solaris may return a relative pathname when the
	193	.\" .I path
	194	.\" argument is relative.
	195	.\" The prototype of
	196	.\" .BR realpath ()
	197	.\" is given in \fI<unistd.h>\fP in libc4 and libc5,
	198	.\" but in \fI<stdlib.h>\fP everywhere else.
	199	.SS GNU extensions
	200	If the call fails with either
	201	.BR EACCES
	202	or
	203	.BR ENOENT
	204	and
	205	.I resolved_path
	206	is not NULL, then the prefix of
	207	.I path
	208	that is not readable or does not exist is returned in
	209	.IR resolved_path .
	210	.SH BUGS
	211	The POSIX.1-2001 standard version of this function is broken by design,
	212	since it is impossible to determine a suitable size for the output buffer,
	213	.IR resolved_path .
	214	According to POSIX.1-2001 a buffer of size
	215	.B PATH_MAX
	216	suffices, but
	217	.B PATH_MAX
	218	need not be a defined constant, and may have to be obtained using
	219	.BR pathconf (3).
	220	And asking
	221	.BR pathconf (3)
	222	does not really help, since, on the one hand POSIX warns that
	223	the result of
	224	.BR pathconf (3)
	225	may be huge and unsuitable for mallocing memory,
	226	and on the other hand
	227	.BR pathconf (3)
	228	may return \-1 to signify that
	229	.B PATH_MAX
	230	is not bounded.
	231	The
	232	.I "resolved_path\ ==\ NULL"
	233	feature, not standardized in POSIX.1-2001,
	234	but standardized in POSIX.1-2008, allows this design problem to be avoided.
	235	.\" .LP
	236	.\" The libc4 and libc5 implementation contained a buffer overflow
	237	.\" (fixed in libc-5.4.13).
	238	.\" Thus, set-user-ID programs like
	239	.\" .BR mount (8)
	240	.\" needed a private version.
	241	.SH SEE ALSO
	242	.BR realpath (1),
	243	.BR readlink (2),
	244	.BR canonicalize_file_name (3),
	245	.BR getcwd (3),
	246	.BR pathconf (3),
	247	.BR sysconf (3)