Simple way to colour alternate output lines in bash

Question

I have need to grep an entire directory for a string, and I get about 50 results. I would like to colour each second line, either text colour or background colour. Best would be a script that I can pipe the output of any command to, and so that it spits out the same (albeit coloured) output.

Answer 1

Not very pretty but does the trick:

(save this to foo.bash and do grep whatever wherever | ./foo.bash

#!/bin/bash
while read line;
do
  echo -e '\e[1;31m'$line;
  read line;
  echo -e '\e[1;32m'$line;
done
echo -en '\e[0m';

Here you can find the list of color codes in bash

Answer 2

Perl is installed on many systems. You could have it alternate for you:

grep -r whatever somedir/ | perl -pe '$_ = "\033[1;29m$_\033[0m" if($. % 2)'

In Perl $. can be substituted with $INPUT_LINE_NUMBER if you prefer readability.

Answer 3

and here is the same in python;

import sys
for line_number,line in enumerate(sys.stdin.readlines()):
    print '%s[1;3%dm%s%s[0m' % (chr(27),(line_number % 2+1),line,chr(27)),

Answer 4

This is to delineate wrapped lines I presume? This shell script uses a background color from the 256 color palette, so as not to interfere with other highlighting that grep --color might do.

#!/bin/sh
c=0
while read line; do
  [ $(($c%2)) -eq 1 ] && printf "\033[48;5;60m"
  printf "%s\033[0m\n" "$line"
  c=$(($c+1))
done

This has the caveat that backslashes etc. within the line will be mangled, so treat this as pseudo code for reimplementation