Nl (Unix)
# Nl (Unix)

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

## History

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 is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.

## Syntax

The command has a number of switches:

* a - number all lines
* t - number lines with printable text only
* n - no line numbering
* string - number only those lines containing the regular expression defined in the string supplied.

The default applied switch is t.

nl also supports some command line options.

## Example

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:

