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32 .\" @(#)ln.1 8.2 (Berkeley) 12/30/93
33 .\" $FreeBSD: head/bin/ln/ln.1 244791 2012-12-28 22:06:33Z gjb $
34 .\"
35 .Dd March 23, 2015
36 .Dt LN 1
37 .Os
38 .Sh NAME
39 .Nm ln ,
40 .Nm link
41 .Nd link files
42 .Sh SYNOPSIS
43 .Nm
44 .Op Fl L | Fl P | Fl s Op Fl F
45 .Op Fl f | iw
46 .Op Fl hnv
47 .Ar source_file
48 .Op Ar target_file
49 .Nm
50 .Op Fl L | Fl P | Fl s Op Fl F
51 .Op Fl f | iw
52 .Op Fl hnv
53 .Ar source_file ...
54 .Ar target_dir
55 .Nm link
56 .Ar source_file Ar target_file
57 .Sh DESCRIPTION
58 The
59 .Nm
60 utility creates a new directory entry (linked file) for the file name
61 specified by
62 .Ar target_file .
63 The
64 .Ar target_file
65 will be created with the same file modes as the
66 .Ar source_file .
67 It is useful for maintaining multiple copies of a file in many places
68 at once without using up storage for the
69 .Dq copies ;
70 instead, a link
71 .Dq points
72 to the original copy.
73 There are two types of links; hard links and symbolic links.
74 How a link
75 .Dq points
76 to a file is one of the differences between a hard and symbolic link.
77 .Pp
78 The options are as follows:
79 .Bl -tag -width flag
80 .It Fl F
81 If the target file already exists and is a directory, then remove it
82 so that the link may occur.
83 The
84 .Fl F
85 option should be used with either
86 .Fl f
87 or
88 .Fl i
89 options.
90 If none is specified,
91 .Fl f
92 is implied.
93 The
94 .Fl F
95 option is a no-op unless
96 .Fl s
97 option is specified.
98 .It Fl L
99 When creating a hard link to a symbolic link,
100 create a hard link to the target of the symbolic link.
101 This is the default.
102 This option cancels the
103 .Fl P
104 option.
105 .It Fl P
106 When creating a hard link to a symbolic link,
107 create a hard link to the symbolic link itself.
108 This option cancels the
109 .Fl L
110 option.
111 .It Fl f
112 If the target file already exists,
113 then unlink it so that the link may occur.
114 (The
115 .Fl f
116 option overrides any previous
117 .Fl i
118 and
119 .Fl w
120 options.)
121 .It Fl h
122 If the
123 .Ar target_file
124 or
125 .Ar target_dir
126 is a symbolic link, do not follow it.
127 This is most useful with the
128 .Fl f
129 option, to replace a symlink which may point to a directory.
130 .It Fl i
131 Cause
132 .Nm
133 to write a prompt to standard error if the target file exists.
134 If the response from the standard input begins with the character
135 .Sq Li y
136 or
137 .Sq Li Y ,
138 then unlink the target file so that the link may occur.
139 Otherwise, do not attempt the link.
140 (The
141 .Fl i
142 option overrides any previous
143 .Fl f
144 options.)
145 .It Fl n
146 Same as
147 .Fl h ,
148 for compatibility with other
149 .Nm
150 implementations.
151 .It Fl s
152 Create a symbolic link.
153 .It Fl v
154 Cause
155 .Nm
156 to be verbose, showing files as they are processed.
157 .It Fl w
158 Warn if the source of a symbolic link does not currently exist.
159 .El
160 .Pp
161 By default,
162 .Nm
163 makes
164 .Em hard
165 links.
166 A hard link to a file is indistinguishable from the original directory entry;
167 any changes to a file are effectively independent of the name used to reference
168 the file.
169 Directories may not be hardlinked, and hard links may not span file systems.
170 .Pp
171 A symbolic link contains the name of the file to
172 which it is linked.
173 The referenced file is used when an
174 .Xr open 2
175 operation is performed on the link.
176 A
177 .Xr stat 2
178 on a symbolic link will return the linked-to file; an
179 .Xr lstat 2
180 must be done to obtain information about the link.
181 The
182 .Xr readlink 2
183 call may be used to read the contents of a symbolic link.
184 Symbolic links may span file systems and may refer to directories.
185 .Pp
186 Given one or two arguments,
187 .Nm
188 creates a link to an existing file
189 .Ar source_file .
190 If
191 .Ar target_file
192 is given, the link has that name;
193 .Ar target_file
194 may also be a directory in which to place the link;
195 otherwise it is placed in the current directory.
196 If only the directory is specified, the link will be made
197 to the last component of
198 .Ar source_file .
199 .Pp
200 Given more than two arguments,
201 .Nm
202 makes links in
203 .Ar target_dir
204 to all the named source files.
205 The links made will have the same name as the files being linked to.
206 .Pp
207 When the utility is called as
208 .Nm link ,
209 exactly two arguments must be supplied,
210 neither of which may specify a directory.
211 No options may be supplied in this simple mode of operation,
212 which performs a
213 .Xr link 2
214 operation using the two passed arguments.
215 .Sh VARIANT SYMLINKS
216 .Dx
217 supports a special kind of dynamic
218 symbolic link called a
219 .Em variant symlink .
220 The
221 .Ar source_file
222 of a variant symlink may contain one or more variable names.
223 Each of these variable names is enclosed in braces and preceded by a
224 dollar sign in the style of variable references in
225 .Xr sh 1
226 and
227 .Xr csh 1 .
228 .Pp
229 Whenever a variant symlink is followed, each variable found in
230 .Ar source_file
231 is replaced by its associated value.
232 In this manner, a variant symlink may resolve to different
233 paths based on context.
234 The facility supports per-process, per-user, and system-wide varsyms.
235 .Pp
236 Varsym variables can be set with the
237 .Xr varsym 1
238 utility.
239 Regular
240 .Xr environ 7
241 environment variables are not used to resolve variant symlinks.
242 .Sh EXAMPLES
243 Create a symbolic link named
244 .Pa /home/src
245 and point it to
246 .Pa /usr/src :
247 .Pp
248 .Dl # ln -s /usr/src /home/src
249 .Pp
250 Hard link
251 .Pa /usr/local/bin/fooprog
252 to file
253 .Pa /usr/local/bin/fooprog-1.0 :
254 .Pp
255 .Dl # ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog
256 .Pp
257 As an exercise, try the following commands:
258 .Bd -literal -offset indent
259 # ls -i /bin/[
260 11553 /bin/[
261 # ls -i /bin/test
262 11553 /bin/test
263 .Ed
264 .Pp
265 Note that both files have the same inode; that is,
266 .Pa /bin/[
267 is essentially an alias for the
268 .Xr test 1
269 command.
270 This hard link exists so
271 .Xr test 1
272 may be invoked from shell scripts, for example, using the
273 .Li "if [ ]"
274 construct.
275 .Pp
276 In the next example, the second call to
277 .Nm
278 removes the original
279 .Pa foo
280 and creates a replacement pointing to
281 .Pa baz :
282 .Bd -literal -offset indent
283 # mkdir bar baz
284 # ln -s bar foo
285 # ln -shf baz foo
286 .Ed
287 .Pp
288 Without the
289 .Fl h
290 option, this would instead leave
291 .Pa foo
292 pointing to
293 .Pa bar
294 and inside
295 .Pa foo
296 create a new symlink
297 .Pa baz
298 pointing to itself.
299 This results from directory-walking.
300 .Pp
301 An easy rule to remember is that the argument order for
302 .Nm
303 is the same as for
304 .Xr cp 1 :
305 The first argument needs to exist, the second one is created.
306 .Pp
307 A simple variable symlink example:
308 .Bd -literal -offset indent
309 sysctl vfs.varsym_enable=1
311 ln -s 'a${fubar}b' test
313 echo 'Hello' > axxb
314 echo 'Goodbye' > ayyb
316 varsym fubar=xx; cat test
317 varsym fubar=yy; cat test
318 .Ed
319 .Sh COMPATIBILITY
320 The
321 .Fl h ,
322 .Fl i ,
323 .Fl n ,
324 .Fl v
325 and
326 .Fl w
327 options are non-standard and their use in scripts is not recommended.
328 They are provided solely for compatibility with other
329 .Nm
330 implementations.
331 .Pp
332 Variant symlinks are unique (among BSDs) to
333 .Dx .
334 .Pp
335 The
336 .Fl F
337 option is a
338 .Fx
339 extension and should not be used in portable scripts.
340 .Sh SEE ALSO
341 .Xr varsym 1 ,
342 .Xr link 2 ,
343 .Xr lstat 2 ,
344 .Xr readlink 2 ,
345 .Xr stat 2 ,
346 .Xr symlink 2 ,
347 .Xr symlink 7
348 .Sh STANDARDS
349 The
350 .Nm
351 utility conforms to
352 .St -p1003.2-92 .
353 .Pp
354 The simplified
355 .Nm link
356 command conforms to
357 .St -susv2 .
358 .Sh HISTORY
359 An
360 .Nm
361 command appeared in
362 .At v1 .