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| 2 | .\" Copyright (c) 1980, 1990, 1993 |
| 3 | .\" The Regents of the University of California. All rights reserved. |
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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 |
| 310 | |
| 311 | ln -s 'a${fubar}b' test |
| 312 | |
| 313 | echo 'Hello' > axxb |
| 314 | echo 'Goodbye' > ayyb |
| 315 | |
| 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 . |