NetBSD/bin/ln/ln.1

.\" $NetBSD: ln.1,v 1.28 2017/04/20 22:57:30 christos Exp $
.\"-
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.\"	@(#)ln.1	8.2 (Berkeley) 12/30/93
.\" $FreeBSD: head/bin/ln/ln.1 244791 2012-12-28 22:06:33Z gjb $
.\"
.Dd April 20, 2017
.Dt LN 1
.Os
.Sh NAME
.\" .Nm ln ,
.\" .Nm link
.Nm ln
.Nd link files
.Sh SYNOPSIS
.Nm
.Op Fl L | Fl P | Fl s Op Fl F
.Op Fl f | iw
.Op Fl hnv
.Ar source_file
.Op Ar target_file
.Nm
.Op Fl L | Fl P | Fl s Op Fl F
.Op Fl f | iw
.Op Fl hnv
.Ar source_file ...
.Ar target_dir
.\" .Nm link
.\" .Ar source_file Ar target_file
.Sh DESCRIPTION
The
.Nm
utility creates a new directory entry (linked file) for the file name
specified by
.Ar target_file .
The
.Ar target_file
will be created with the same file modes as the
.Ar source_file .
It is useful for maintaining multiple copies of a file in many places
at once without using up storage for the
.Dq copies ;
instead, a link
.Dq points
to the original copy.
There are two types of links; hard links and symbolic links.
How a link
.Dq points
to a file is one of the differences between a hard and symbolic link.
.Pp
The options are as follows:
.Bl -tag -width flag
.It Fl F
If the target file already exists and is a directory, then remove it
so that the link may occur.
The
.Fl F
option should be used with either
.Fl f
or
.Fl i
options.
If none is specified,
.Fl f
is implied.
The
.Fl F
option is a no-op unless
.Fl s
option is specified.
.It Fl L
When creating a hard link to a symbolic link,
create a hard link to the target of the symbolic link.
This is the default.
This option cancels the
.Fl P
option.
.It Fl P
When creating a hard link to a symbolic link,
create a hard link to the symbolic link itself.
This option cancels the
.Fl L
option.
.It Fl f
If the target file already exists,
then unlink it so that the link may occur.
(The
.Fl f
option overrides any previous
.Fl i
and
.Fl w
options.)
.It Fl h
If the
.Ar target_file
or
.Ar target_dir
is a symbolic link, do not follow it.
This is most useful with the
.Fl f
option, to replace a symlink which may point to a directory.
.It Fl i
Cause
.Nm
to write a prompt to standard error if the target file exists.
If the response from the standard input begins with the character
.Sq Li y
or
.Sq Li Y ,
then unlink the target file so that the link may occur.
Otherwise, do not attempt the link.
(The
.Fl i
option overrides any previous
.Fl f
options.)
.It Fl n
Same as
.Fl h ,
for compatibility with other
.Nm
implementations.
.It Fl s
Create a symbolic link.
.It Fl v
Cause
.Nm
to be verbose, showing files as they are processed.
.It Fl w
Warn if the source of a symbolic link does not currently exist.
.El
.Pp
By default,
.Nm
makes
.Em hard
links.
A hard link to a file is indistinguishable from the original directory entry;
any changes to a file are effectively independent of the name used to reference
the file.
Directories may not be hardlinked, and hard links may not span file systems.
.Pp
A symbolic link contains the name of the file to
which it is linked.
The referenced file is used when an
.Xr open 2
operation is performed on the link.
A
.Xr stat 2
on a symbolic link will return the linked-to file; an
.Xr lstat 2
must be done to obtain information about the link.
The
.Xr readlink 2
call may be used to read the contents of a symbolic link.
Symbolic links may span file systems and may refer to directories.
.Pp
Given one or two arguments,
.Nm
creates a link to an existing file
.Ar source_file .
If
.Ar target_file
is given, the link has that name;
.Ar target_file
may also be a directory in which to place the link;
otherwise it is placed in the current directory.
If only the directory is specified, the link will be made
to the last component of
.Ar source_file .
.Pp
Given more than two arguments,
.Nm
makes links in
.Ar target_dir
to all the named source files.
The links made will have the same name as the files being linked to.
.\" .Pp
.\" When the utility is called as
.\" .Nm link ,
.\" exactly two arguments must be supplied,
.\" neither of which may specify a directory.
.\" No options may be supplied in this simple mode of operation,
.\" which performs a
.\" .Xr link 2
.\" operation using the two passed arguments.
.Sh EXAMPLES
Create a symbolic link named
.Pa /home/src
and point it to
.Pa /usr/src :
.Pp
.Dl # ln -s /usr/src /home/src
.Pp
Hard link
.Pa /usr/local/bin/fooprog
to file
.Pa /usr/local/bin/fooprog-1.0 :
.Pp
.Dl # ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog
.Pp
As an exercise, try the following commands:
.Bd -literal -offset indent
# ls -i /bin/[
11553 /bin/[
# ls -i /bin/test
11553 /bin/test
.Ed
.Pp
Note that both files have the same inode; that is,
.Pa /bin/[
is essentially an alias for the
.Xr test 1
command.
This hard link exists so
.Xr test 1
may be invoked from shell scripts, for example, using the
.Li "if [ ]"
construct.
.Pp
In the next example, the second call to
.Nm
removes the original
.Pa foo
and creates a replacement pointing to
.Pa baz :
.Bd -literal -offset indent
# mkdir bar baz
# ln -s bar foo
# ln -shf baz foo
.Ed
.Pp
Without the
.Fl h
option, this would instead leave
.Pa foo
pointing to
.Pa bar
and inside
.Pa foo
create a new symlink
.Pa baz
pointing to itself.
This results from directory-walking.
.Pp
An easy rule to remember is that the argument order for
.Nm
is the same as for
.Xr cp 1 :
The first argument needs to exist, the second one is created.
.Sh COMPATIBILITY
The
.Fl h ,
.Fl i ,
.Fl n ,
.Fl v
and
.Fl w
options are non-standard and their use in scripts is not recommended.
They are provided solely for compatibility with other
.Nm
implementations.
.Pp
The
.Fl F
option is a
.Fx
extension and should not be used in portable scripts.
.Sh SEE ALSO
.Xr link 2 ,
.Xr lstat 2 ,
.Xr readlink 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Nm
utility conforms to
.St -p1003.2-92 .
.\" .Pp
.\" The simplified
.\" .Nm link
.\" command conforms to
.\" .St -susv2 .
.Sh HISTORY
An
.Nm
command appeared in
.At v1 .