Nl (Unix)

nl is a Unix utility for numbering lines, either from a file or from standard input, reproducing output on standard output.

It has a number of switches:

The default applied switch is t.

nl also supports some command line options.

The following example numbers only the lines that begin with a capital letter A (matching on the regular expression /^A/). filename is optional.

It can be useful as an alternative to grep -n: