|Operating system||Unix and Unix-like|
nl is a Unix utility for numbering lines, either from a file or from standard input, reproducing output on standard output.
nl is part of the X/Open Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX.1 and the Single Unix Specification. It first appeared in System V release 2.
The version of
nl bundled in GNU coreutils was written by Scott Bartram and David MacKenzie.
The command has a number of switches:
The default applied switch is t.
nl also supports some command line options.
$ nl tf 1 echo press cr 2 read cr 3 done
The following example numbers only the lines that begin with a capital letter A (matching on the regular expression /^A/). filename is optional.
$ nl -b p^A filename apple 1 Apple BANANA 2 Allspice strawberry
It can be useful as an alternative to grep -n:
$ cat somefile aaaa bbbb cccc dddc $ nl somefile | grep cccc 3 cccc