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.\" Copyright (C) 1999 Andries Brouwer (aeb@cwi.nl)
.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.\" Rewritten old page, 990824, aeb@cwi.nl
.\"
.TH REALPATH 3 1999-08-24 "" "Linux Programmer's Manual"
.SH NAME
realpath \- return the canonicalized absolute pathname
.SH SYNOPSIS
.nf
.B #include <limits.h>
.B #include <stdlib.h>
.sp
.BI "char *realpath(const char *" path ", char *" resolved_path );
.SH DESCRIPTION
.B realpath
expands all symbolic links and resolves references
to
.IR '/./' ", " '/../'
and extra
.I '/'
characters in the null terminated string named by
.I path
and stores the canonicalized absolute pathname in the buffer of size
.B PATH_MAX
named by
.IR resolved_path .
The resulting path will have no symbolic link,
.I '/./'
or
.I '/../'
components.
.SH "RETURN VALUE"
If there is no error, it returns a pointer to the
.IR resolved_path .
Otherwise it returns a NULL pointer, and the contents
of the array
.I resolved_path
are undefined. The global variable
.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
Either
.I path
or
.I resolved_path
is NULL. (In libc5 this would just cause a segfault.)
.TP
.B EIO
An I/O error occurred while reading from the file system.
.TP
.B ELOOP
Too many symbolic links were encountered in translating the pathname.
.TP
.B ENAMETOOLONG
A component of a path name exceeded
.B NAME_MAX
characters, or an entire path name exceeded
.B PATH_MAX
characters.
.TP
.B ENOENT
The named file does not exist.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.SH BUGS
Never use this function. It is broken by design since it is
impossible to determine a suitable size for the output buffer.
According to POSIX a buffer of size PATH_MAX suffices, but
PATH_MAX need not be a defined constant, and may have to be
obtained using
.IR pathconf() .
And asking
.I pathconf()
does not really help, since on the one hand POSIX warns that
the result of
.I pathconf()
may be huge and unsuitable for mallocing memory. And on the other
hand
.I pathconf()
may return \-1 to signify that PATH_MAX is not bounded.
.LP
The libc4 and libc5 implementation contains a buffer overflow
(fixed in libc-5.4.13).
Thus, suid programs like mount need a private version.
.SH HISTORY
The
.B realpath
function first appeared in BSD 4.4, contributed by Jan-Simon Pendry.
In Linux this function appears in libc 4.5.21.
.SH "CONFORMING TO"
In BSD 4.4 and Solaris the limit on the pathname length is MAXPATHLEN
(found in <sys/param.h>). The SUSv2 prescribes PATH_MAX and
NAME_MAX, as found in <limits.h> or provided by the
.I pathconf()
function. A typical source fragment would be
.LP
.RS
.nf
#ifdef PATH_MAX
path_max = PATH_MAX;
#else
path_max = pathconf (path, _PC_PATH_MAX);
if (path_max <= 0)
path_max = 4096;
#endif
.fi
.RE
(But see the BUGS section.)
.LP
The BSD 4.4, Linux and SUSv2 versions always return an absolute
path name. Solaris may return a relative path name when the
.I path
argument is relative.
The prototype of
.B realpath
is given in <unistd.h> in libc4 and libc5,
but in <stdlib.h> everywhere else.
.SH "SEE ALSO"
.BR readlink (2),
.BR getcwd (3),
.BR pathconf (3),
.BR sysconf (3)
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