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:
- 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 a number of 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
- wc - the word count command
- cat - concatenate command (-n flag is equivalent to nl -a)
- List of Unix programs