.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "LN" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" ln 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
ln \- link files
.SH SYNOPSIS
.LP
\fBln\fP \fB[\fP\fB-fs\fP\fB]\fP \fIsource_file target_file\fP\fB
.br
.sp
ln\fP \fB[\fP\fB-fs\fP\fB]\fP \fIsource_file\fP \fB...\fP \fItarget_dir\fP\fB
.br
\fP
.SH DESCRIPTION
.LP
In the first synopsis form, the \fIln\fP utility shall create a new
directory entry (link) at the destination path specified by
the \fItarget_file\fP operand. If the \fB-s\fP option is specified,
a symbolic link shall be created for the file specified by
the \fIsource_file\fP operand. This first synopsis form shall be assumed
when the final operand does not name an existing
directory; if more than two operands are specified and the final is
not an existing directory, an error shall result.
.LP
In the second synopsis form, the \fIln\fP utility shall create a new
directory entry (link), or if the \fB-s\fP option is
specified a symbolic link, for each file specified by a \fIsource_file\fP
operand, at a destination path in the existing directory
named by \fItarget_dir\fP.
.LP
If the last operand specifies an existing file of a type not specified
by the System Interfaces volume of
IEEE\ Std\ 1003.1-2001, the behavior is implementation-defined.
.LP
The corresponding destination path for each \fIsource_file\fP shall
be the concatenation of the target directory pathname, a
slash character, and the last pathname component of the \fIsource_file\fP.
The second synopsis form shall be assumed when the
final operand names an existing directory.
.LP
For each \fIsource_file\fP:
.IP " 1." 4
If the destination path exists:
.RS
.IP " a." 4
If the \fB-f\fP option is not specified, \fIln\fP shall write a diagnostic
message to standard error, do nothing more with the
current \fIsource_file\fP, and go on to any remaining \fIsource_files\fP.
.LP
.IP " b." 4
Actions shall be performed equivalent to the \fIunlink\fP() function
defined in the
System Interfaces volume of IEEE\ Std\ 1003.1-2001, called using \fIdestination\fP
as the \fIpath\fP argument. If this
fails for any reason, \fIln\fP shall write a diagnostic message to
standard error, do nothing more with the current
\fIsource_file\fP, and go on to any remaining \fIsource_files\fP.
.LP
.RE
.LP
.IP " 2." 4
If the \fB-s\fP option is specified, \fIln\fP shall create a symbolic
link named by the destination path and containing as its
pathname \fIsource_file\fP. The \fIln\fP utility shall do nothing
more with \fIsource_file\fP and shall go on to any remaining
files.
.LP
.IP " 3." 4
If \fIsource_file\fP is a symbolic link, actions shall be performed
equivalent to the \fIlink\fP() function using the object that \fIsource_file\fP
references as the \fIpath1\fP
argument and the destination path as the \fIpath2\fP argument. The
\fIln\fP utility shall do nothing more with \fIsource_file\fP
and shall go on to any remaining files.
.LP
.IP " 4." 4
Actions shall be performed equivalent to the \fIlink\fP() function
defined in the System
Interfaces volume of IEEE\ Std\ 1003.1-2001 using \fIsource_file\fP
as the \fIpath1\fP argument, and the destination path
as the \fIpath2\fP argument.
.LP
.SH OPTIONS
.LP
The \fIln\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following option shall be supported:
.TP 7
\fB-f\fP
Force existing destination pathnames to be removed to allow the link.
.TP 7
\fB-s\fP
Create symbolic links instead of hard links.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIsource_file\fP
A pathname of a file to be linked. If the \fB-s\fP option is specified,
no restrictions on the type of file or on its
existence shall be made. If the \fB-s\fP option is not specified,
whether a directory can be linked is
implementation-defined.
.TP 7
\fItarget_file\fP
The pathname of the new directory entry to be created.
.TP 7
\fItarget_dir\fP
A pathname of an existing directory in which the new directory entries
are created.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIln\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
Not used.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
All the specified files were linked successfully.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
None.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
Some historic versions of \fIln\fP (including the one specified by
the SVID) unlink the destination file, if it exists, by
default. If the mode does not permit writing, these versions prompt
for confirmation before attempting the unlink. In these
versions the \fB-f\fP option causes \fIln\fP not to attempt to prompt
for confirmation.
.LP
This allows \fIln\fP to succeed in creating links when the target
file already exists, even if the file itself is not writable
(although the directory must be). Early proposals specified this functionality.
.LP
This volume of IEEE\ Std\ 1003.1-2001 does not allow the \fIln\fP
utility to unlink existing destination paths by
default for the following reasons:
.IP " *" 3
The \fIln\fP utility has historically been used to provide locking
for shell applications, a usage that is incompatible with
\fIln\fP unlinking the destination path by default. There was no corresponding
technical advantage to adding this
functionality.
.LP
.IP " *" 3
This functionality gave \fIln\fP the ability to destroy the link structure
of files, which changes the historical behavior of
\fIln\fP.
.LP
.IP " *" 3
This functionality is easily replicated with a combination of \fIrm\fP
and \fIln\fP.
.LP
.IP " *" 3
It is not historical practice in many systems; BSD and BSD-derived
systems do not support this behavior. Unfortunately,
whichever behavior is selected can cause scripts written expecting
the other behavior to fail.
.LP
.IP " *" 3
It is preferable that \fIln\fP perform in the same manner as the \fIlink\fP()
function,
which does not permit the target to exist already.
.LP
.LP
This volume of IEEE\ Std\ 1003.1-2001 retains the \fB-f\fP option
to provide support for shell scripts depending on the
SVID semantics. It seems likely that shell scripts would not be written
to handle prompting by \fIln\fP and would therefore have
specified the \fB-f\fP option.
.LP
The \fB-f\fP option is an undocumented feature of many historical
versions of the \fIln\fP utility, allowing linking to
directories. These versions require modification.
.LP
Early proposals of this volume of IEEE\ Std\ 1003.1-2001 also required
a \fB-i\fP option, which behaved like the
\fB-i\fP options in \fIcp\fP and \fImv\fP, prompting for
confirmation before unlinking existing files. This was not historical
practice for the \fIln\fP utility and has been omitted.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIchmod\fP(), \fIfind\fP, \fIpax\fP, \fIrm\fP, the System Interfaces
volume of IEEE\ Std\ 1003.1-2001, \fIlink\fP(), \fIunlink\fP()
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .