Piping a command through a color filter

Question

Does something like this exist in Unix?

$ echo "this should show in red" | red
$ echo "this should show in green" | green
$ echo "this should show in blue" | blue

Here I don't mean for literal color code text to come up (to be pasted in a file, for example). I just mean for the text to actually show up in the terminal as that color. Is this possible?

Solution 1

Here's a little script that does just that. Save this as color in a directory in your $PATH (for example, ~/bin if that's in your $PATH):

#!/usr/bin/env perl

use strict;
use warnings;
use Term::ANSIColor; 

my $color=shift;
while (<>) {
    print color("$color").$_.color("reset");
} 

Then, pass your text through the script, giving . as the pattern to match and specifying a color:

The supported colors depend on the abilities of your terminal. For more details, see the documentation of the Term::ANSIColor package.

Solution 2

You'd use tput for that:

tput setaf 1
echo This is red
tput sgr0
echo This is back to normal

This can be used to build a pipe:

red() { tput setaf 1; cat; tput sgr0; }
echo This is red | red

The basic colours are respectively black (0), red (1), green, yellow, blue, magenta, cyan and white (7). You'll find all the details in the terminfo(5) manpage.

Solution 3

With zsh:

autoload colors; colors
for color (${(k)fg})
  eval "$color() {print -n \$fg[$color]; cat; print -n \$reset_color}"

And then:

$ echo "while" | blue
while

Solution 4

(as discussed in comments, use tput instead if you have it)

Using bourne shell and echo (built-in) command which understands the ANSI escape \e with -e option:

black()  { IFS= ; while read -r line; do echo -e '\e[30m'$line'\e[0m'; done; }
red()    { IFS= ; while read -r line; do echo -e '\e[31m'$line'\e[0m'; done; }
green()  { IFS= ; while read -r line; do echo -e '\e[32m'$line'\e[0m'; done; }
yellow() { IFS= ; while read -r line; do echo -e '\e[33m'$line'\e[0m'; done; }
blue()   { IFS= ; while read -r line; do echo -e '\e[34m'$line'\e[0m'; done; }
purple() { IFS= ; while read -r line; do echo -e '\e[35m'$line'\e[0m'; done; }
cyan()   { IFS= ; while read -r line; do echo -e '\e[36m'$line'\e[0m'; done; }
white()  { IFS= ; while read -r line; do echo -e '\e[37m'$line'\e[0m'; done; }

echo '    foo\n    bar' | red

or, more generic shell script (say, /usr/local/bin/colorize):

#!/bin/sh

usage() {
    echo 'usage:' >&2
    echo '  some-command | colorize {black, red, green, yellow, blue, purple, cyan, white}' >&2
    exit 1
}

[ -z "$1" ] && usage

case $1 in
    black)  color='\e[30m' ;;
    red)    color='\e[31m' ;;
    green)  color='\e[32m' ;;
    yellow) color='\e[33m' ;;
    blue)   color='\e[34m' ;;
    purple) color='\e[35m' ;;
    cyan)   color='\e[36m' ;;
    white)  color='\e[36m' ;;
    *) usage ;;
esac

IFS=
while read -r line; do
    echo -e $color$line'\e[0m'
done

IFS= is needed to prevent whitespace trimming (see POSIX for details).

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Comments

[Gaétan RYCKEBOER]

Is there a list of colors that are valid to pass in somewhere?

[Vlastimil Burián]

This is completely non-portable solution. I mean you should adhere to POSIX.

[wataash]

Sure, if we could. It's intended to be used on embedded systems or rescue environments like busybox. I decided to write this answer because I believe these code snippets are useful in some situations -- at least for busybox users and for me, who had to output colors only with shell's built-in commands on an embedded environment today.

[wataash]

forgot to say that ordinary busybox doesn't have tput.

[jvriesem]

I don't know perl. Why doesn't color rgb012 work and give me some kind of teal/turquoise color?