323 lines
7.3 KiB
Groff
323 lines
7.3 KiB
Groff
.\"-
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.\" Copyright (c) 1980, 1990, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the Institute of Electrical and Electronics Engineers, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)ln.1 8.2 (Berkeley) 12/30/93
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.\" $FreeBSD$
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.\"
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.Dd June 12, 2017
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.Dt LN 1
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.Os
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.Sh NAME
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.Nm ln ,
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.Nm link
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.Nd link files
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.Sh SYNOPSIS
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.Nm
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.Op Fl L | Fl P | Fl s Op Fl F
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.Op Fl f | iw
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.Op Fl hnv
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.Ar source_file
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.Op Ar target_file
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.Nm
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.Op Fl L | Fl P | Fl s Op Fl F
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.Op Fl f | iw
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.Op Fl hnv
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.Ar source_file ...
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.Ar target_dir
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.Nm link
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.Ar source_file Ar target_file
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.Sh DESCRIPTION
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The
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.Nm
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utility creates a new directory entry (linked file) for the file name
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specified by
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.Ar target_file .
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The
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.Ar target_file
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will be created with the same file modes as the
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.Ar source_file .
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It is useful for maintaining multiple copies of a file in many places
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at once without using up storage for the
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.Dq copies ;
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instead, a link
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.Dq points
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to the original copy.
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There are two types of links; hard links and symbolic links.
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How a link
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.Dq points
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to a file is one of the differences between a hard and symbolic link.
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.Pp
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The options are as follows:
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.Bl -tag -width flag
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.It Fl F
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If the target file already exists and is a directory, then remove it
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so that the link may occur.
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The
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.Fl F
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option should be used with either
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.Fl f
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or
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.Fl i
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options.
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If neither
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.Fl f
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nor
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.Fl i
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is specified,
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.Fl f
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is implied.
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The
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.Fl F
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option is a no-op unless
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.Fl s
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is specified.
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.It Fl L
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When creating a hard link to a symbolic link,
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create a hard link to the target of the symbolic link.
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This is the default.
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This option cancels the
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.Fl P
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option.
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.It Fl P
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When creating a hard link to a symbolic link,
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create a hard link to the symbolic link itself.
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This option cancels the
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.Fl L
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option.
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.It Fl f
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If the target file already exists,
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then unlink it so that the link may occur.
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(The
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.Fl f
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option overrides any previous
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.Fl i
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and
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.Fl w
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options.)
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.It Fl h
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If the
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.Ar target_file
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or
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.Ar target_dir
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is a symbolic link, do not follow it.
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This is most useful with the
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.Fl f
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option, to replace a symlink which may point to a directory.
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.It Fl i
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Cause
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.Nm
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to write a prompt to standard error if the target file exists.
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If the response from the standard input begins with the character
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.Sq Li y
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or
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.Sq Li Y ,
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then unlink the target file so that the link may occur.
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Otherwise, do not attempt the link.
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(The
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.Fl i
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option overrides any previous
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.Fl f
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options.)
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.It Fl n
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Same as
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.Fl h ,
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for compatibility with other
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.Nm
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implementations.
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.It Fl s
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Create a symbolic link.
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.It Fl v
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Cause
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.Nm
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to be verbose, showing files as they are processed.
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.It Fl w
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Warn if the source of a symbolic link does not currently exist.
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.El
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.Pp
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By default,
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.Nm
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makes
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.Em hard
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links.
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A hard link to a file is indistinguishable from the original directory entry;
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any changes to a file are effectively independent of the name used to reference
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the file.
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Directories may not be hardlinked, and hard links may not span file systems.
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.Pp
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A symbolic link contains the name of the file to
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which it is linked.
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The referenced file is used when an
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.Xr open 2
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operation is performed on the link.
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A
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.Xr stat 2
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on a symbolic link will return the linked-to file; an
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.Xr lstat 2
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must be done to obtain information about the link.
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The
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.Xr readlink 2
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call may be used to read the contents of a symbolic link.
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Symbolic links may span file systems and may refer to directories.
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.Pp
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Given one or two arguments,
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.Nm
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creates a link to an existing file
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.Ar source_file .
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If
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.Ar target_file
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is given, the link has that name;
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.Ar target_file
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may also be a directory in which to place the link;
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otherwise it is placed in the current directory.
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If only the directory is specified, the link will be made
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to the last component of
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.Ar source_file .
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.Pp
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Given more than two arguments,
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.Nm
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makes links in
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.Ar target_dir
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to all the named source files.
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The links made will have the same name as the files being linked to.
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.Pp
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When the utility is called as
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.Nm link ,
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exactly two arguments must be supplied,
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neither of which may specify a directory.
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No options may be supplied in this simple mode of operation,
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which performs a
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.Xr link 2
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operation using the two passed arguments.
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.Sh EXAMPLES
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Create a symbolic link named
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.Pa /home/src
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and point it to
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.Pa /usr/src :
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.Pp
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.Dl # ln -s /usr/src /home/src
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.Pp
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Hard link
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.Pa /usr/local/bin/fooprog
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to file
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.Pa /usr/local/bin/fooprog-1.0 :
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.Pp
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.Dl # ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog
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.Pp
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As an exercise, try the following commands:
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.Bd -literal -offset indent
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# ls -i /bin/[
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11553 /bin/[
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# ls -i /bin/test
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11553 /bin/test
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.Ed
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.Pp
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Note that both files have the same inode; that is,
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.Pa /bin/[
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is essentially an alias for the
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.Xr test 1
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command.
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This hard link exists so
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.Xr test 1
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may be invoked from shell scripts, for example, using the
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.Li "if [ ]"
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construct.
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.Pp
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In the next example, the second call to
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.Nm
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removes the original
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.Pa foo
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and creates a replacement pointing to
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.Pa baz :
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.Bd -literal -offset indent
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# mkdir bar baz
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# ln -s bar foo
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# ln -shf baz foo
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.Ed
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.Pp
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Without the
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.Fl h
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option, this would instead leave
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.Pa foo
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pointing to
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.Pa bar
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and inside
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.Pa foo
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create a new symlink
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.Pa baz
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pointing to itself.
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This results from directory-walking.
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.Pp
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An easy rule to remember is that the argument order for
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.Nm
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is the same as for
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.Xr cp 1 :
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The first argument needs to exist, the second one is created.
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.Sh COMPATIBILITY
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The
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.Fl h ,
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.Fl i ,
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.Fl n ,
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.Fl v
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and
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.Fl w
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options are non-standard and their use in scripts is not recommended.
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They are provided solely for compatibility with other
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.Nm
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implementations.
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.Pp
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The
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.Fl F
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option is a
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.Fx
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extension and should not be used in portable scripts.
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.Sh SEE ALSO
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.Xr link 2 ,
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.Xr lstat 2 ,
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.Xr readlink 2 ,
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.Xr stat 2 ,
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.Xr symlink 2 ,
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.Xr symlink 7
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.Sh STANDARDS
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The
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.Nm
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utility conforms to
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.St -p1003.2-92 .
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.Pp
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The simplified
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.Nm link
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command conforms to
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.St -susv2 .
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.Sh HISTORY
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An
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.Nm
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command appeared in
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.At v1 .
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