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.
The default applied switch is t.
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 (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 : $ cat somefile aaaa bbbb cccc dddc $ nl -ba somefile | grep cccc 3 cccc
See also wc (Unix) – the word count command cat (Unix) – concatenate command (-n flag is equivalent to nl -a) List of Unix commands
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