.\" Copyright (C) 1999 Andries Brouwer (aeb@cwi.nl)
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.TH REALPATH 3  "24 August 1999" "" "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
The libc4 and libc5 implementation contains a buffer overflow
(fixed in libc-5.4.13).
Thus, suid programs like mount need a private version.
.LP
The length of the output buffer should have been an additional
parameter, especially since
.BR pathconf (3)
warns that the result of
.I pathconf()
may be huge and unsuitable for mallocing memory.
.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
.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)