#!/usr/bin/perl -p

#  #  #  #    #  awk '{ print NR, $0 }'
#  #  #  #
#  #  #  #  #!/bin/bash
#  #  #  #  nl "$1"
#  #  #  
#  #  #  $a = 1;
#  #  #  while (<>) {
#  #  #    print $a++, " ", $_;
#  #  #  }
#  #  
#  #  $_ = ++$a . " " . $_
#  
#  s/^(.*)$/$. $1/  # best? 

s/^.*$/$. $&/  # slower but shorter