title: Nl (Unix)
text: # Nl (Unix)
  
  nl is a Unix utility for numbering lines, either from a file or from standard input, reproducing output on standard output.
  
  ## History
  
  nl 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
  * string - 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
  
  The following example numbers only the lines that begin with a capital letter A (matching on the regular expression /^A/). filename is optional.
  
  It can be useful as an alternative to grep -n:
  
  