Nl (Unix)

nl is a Unix utility for numbering lines, either from a file or from standard input, reproducing output on standard output.
History.
 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 codice_1 bundled in GNU coreutils was written by Scott Bartram and David MacKenzie.
Syntax.
The command has a number of switches:
The default applied switch is "t".
nl also supports some command line options.
Example.
 $ 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