ln(1) — Commands
NAME
ln − link to a file
SYNOPSIS
ln [-fs] sourcename [targetname]
ln [-fs] sourcename... targetdirectory
ln [-fns] sourcename targetname
ln [-fns] sourcename... targetdirectory
The -n flag is valid only if the environment variable CMD_ENV is set to svr4.
FLAGS
−fForces the removal of existing target pathnames before linking.
−sCreates symbolic links.
−nIf the target already exists, do not create the link, and issue an error message. −f overrides −n. Requires the environment variable CMD_ENV to be set to svr4. This mimics the behavior of the ln command with no flags when CMD_ENV is not set.
DESCRIPTION
A link is a directory entry that refers to a file. Typically, sourcename is an existing file, and targetname does not exist. targetname becomes a new name, or pseudonym, for sourcename. A file, together with its size and all its protection information, can have several links to it. There are two kinds of links: hard links and symbolic links.
By default ln makes hard links. A hard link to a file is indistinguishable from the original directory entry. Changes to either file affect both files. Hard links cannot span file systems and cannot refer to directories.
A symbolic link contains the name of the file to which it is linked. The referenced file is used when an open(2) operation is performed on the link. A stat(2) on a symbolic link returns the linked-to file. An lstat(2) must be done to obtain information about the link. The readlink(2) call can be used to read the contents of a symbolic link. Symbolic links can span file systems and can refer to directories.
Given one or two arguments, ln creates a link to an existing sourcename file. If targetname is omitted, then sourcename is used for the link, but it must be created in a different directory than that of the source file. If targetname is given, the link has that name. The targetname can 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 is made to the last component of the sourcename file.
Given more than two arguments, ln makes links to all the specified files (sourcename) in the specified directory (targetdirectory). The links made have the same name as the files to which they are being linked.
If targetname exits, the command will abort unless the −f flag is set.
SVID and System V Release 4 Conformance
When the environment variable CMD_ENV is set to svr4, the behavior of the base ln command is compatible with its behavior under System V Release 4. There is also a version of the ln command provided in the System V habitat that is conformant with the SVID standard. For more information on the System V habitat, see the Command and Shell User’s Guide. This section documents the behavior of the habitat version, and of the base version with CMD_ENV set to svr4, insofar as the behavior differs from that of the base ln command without CMD_ENV so set. This section discusses only hard links.
In contrast to the base ln command without CMD_ENV set, these versions of ln will silently overwrite an existing targetname if it is not a directory and has write permission. The -n flag, available only in the base command when CMD_ENV is set, prevents overwriting such an existing target. Thus, for such an existing targetname, the base command ln -n with CMD_ENV set behaves the same as does the base command ln with no flags and with CMD_ENV not set.
If the targetname exists, is not a directory, and does not have write permission, three possible conditions can exist, with each condition producing a different behavior:
•If the standard input is not a terminal, the command attempts to silently unlink targetname and link the source file to it.
•If the standard input is a terminal and the command line does not include the -f option, the command prompts the user for permission to unlink targetname. The habitat command compares the user response to the system defined values for YESSTR and NOSTR. If the user response matches the value for YESSTR, the command attempts to unlink the target file and link the source file to targetname. If the user response matches NOSTR, the command aborts. Similarly, with the base command and CMD_ENV set, the operation aborts unless the user response begins with a y.
•If the standard input is a terminal and the command line includes the -f option, the command attempts to silently unlink targetname and link the source file to it.
NOTES
You cannot link files across file systems without using the -s flag.
EXAMPLES
1.The following example creates a link (also called an alias) to a file:
ln chap1 intro
The previous command links chap1 to the intro file. If intro does not already exist, the filename is created. If intro does exist and permissions allow, the file is replaced by a link to chap1. The following command forces the link even if intro exists and permissions do not allow it to be overwritten:
ln -f chap1 intro
The previous command causes chap1 and intro to refer to the same file. Any changes made to one file also appear in the other file. If one name is deleted with the rm command, the file is not actually deleted because it remains under the other name.
2.The following command links a file to the same name in an existing directory:
ln index manual
The previous command links index to the new name manual/index.
3.The following command links several files to names in another directory:
ln chap2 jim/chap3 /u/manual
The previous command links chap2 to the new name /u/manual/chap2 and links jim/chap3 to /u/manual/chap3.
4.The following command uses ln with pattern-matching characters:
ln manual/∗ .
The previous command links all files in the directory manual into the current directory (.), giving them the same names they have in manual. Note that you must type a space between the ∗ (asterisk) and the . (dot).
5.The following command creates a link to the final component of a pathname:
ln -s /a/b/c/d/e
This creates a link, e, in the current directory to the file /a/b/c/d/e.
RELATED INFORMATION
Commands: cp(1), mv(1), rm(1).
Functions: chmod(2), link(2), readlink(2), symlink(2), unlink(2).