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:

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.

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

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List of Unix utilities