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
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
- pstring - number only those lines containing the regular expression defined in the string supplied.
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. filename is optional.
$ nl -b p^A filename
apple
1 Apple
BANANA
2 Allspice
strawberry
It can be useful as an alternative to :
$ cat somefile
aaaa
bbbb
cccc
dddc
$ nl -ba somefile | grep cccc
3 cccc