Many command on the Unix/Linux command line will print out text in various colors. For example the ls command accepts a --color flag and then it adds color to the file-system listings. You can convince your prompt to change color based on some condition. e.g. the weather outside.

How can you create such colorful output with Perl and how could you do it manually?

The key to this is the ANSI escape code tabel where you can find how to give instructions to the screen of a command-line window. Some of these instructions are related to color.

Here is an example script:

examples/colors.pl

use strict;
use warnings;
use feature 'say';

my $black   = "\033[0;30m";
my $red     = "\033[0;31m";
my $green   = "\033[0;32m";
my $yellow  = "\033[0;33m";
my $white   = "\033[0;37m";
my $nocolor = "\033[0m";

say("Plain text in the default color");
say($green);
say("Green text");
say($red);
say("Red text");
say("$yellow yellow $green green $red red");
say($white);
say("White text");
say($black);
say("Black text");

Here I selected a few colors from the ANSI escape code table and put them in plain scalar variables. Then I only needed to print them to the screeen.

Running this script: 

perl colors.pl

resulted in the following output on my computer:

ansi colored output text

Color file content manually

If I run the same script and redirect the output to a file 

perl color.pl > colors.txt

I'll get a "regular" text file that looks like this if I open it with any regular editor. e.g. vim.

examples/colors.txt

Plain text in the default color

Green text

Red text
 yellow  green  red

White text

Black text

However using cat to display the file will evaluate the ANSI escape codes 

cat colors.txt

and you will see the same as previously when we ran the Perl script.

ansi colored output text

However you don't need a Perl script to create the file. You can edit it manually as well.

The more command gives you the same colorful result: 

more colors.txt

However, these ANSI escape codes confuse the less command: 

less colors.txt
"colors.txt" may be a binary file.  See it anyway?

less -rf and Term::ANSIColor

After posting this article I received a comment from Thomas Köhler telling me that less -r would show the color. That helped me overcome my lazyness and checked the manual page of less. I found that the -f flag would suppress the may be a binary file. See it anyway? warning. So you can use 

less -rf colors.txt

He also showed two other ways to use ANSI colors in Perl.