nl (Unix)

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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[edit]

 $ 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

See also[edit]

External links[edit]