Prefix shell command output with a colored string (supports stderr)

prefix.sh

#!/bin/bash

raw_prefix="$1"
prefix_width=${PREFIX_WIDTH:-20}
color=color_${PREFIX_COLOR:-green}
error_color=color_${PREFIX_ERROR_COLOR:-red}
shift 1

if [ "$raw_prefix" = "" ]; then
	echo "USAGE: $0 <prefix> <command> [args..]"
	echo
	echo "If prefix is '-', then the command itself will be used as prefix."
	echo
	echo "Environment vars:"
	echo "  PREFIX_WIDTH - formatted width of prefix (default 20, you can use 0)"
	echo "  PREFIX_COLOR - one of: black red green yellow blue purple cyan white none (default: green)"
	echo "  PREFIX_ERROR_COLOR - color used for stderr (default: red)"
	echo
	echo "Advanced examples:"
	echo '  seq 12 | parallel prefix - echo "input was {}"'
	echo '  echo -n http://example.com/a.txt http://example.com/b.txt | parallel -d ' ' prefix {} wget {}'
	exit 1
fi

if [ "$raw_prefix" = "-" ]; then
	raw_prefix="$*"
fi

color_reset='\x1B[0m' # Text Reset

color_black='\x1B[1;30m';
color_red='\x1B[1;31m';
color_green='\x1B[1;32m';
color_yellow='\x1B[1;33m';
color_blue='\x1B[1;34m';
color_purple='\x1B[1;35m';
color_cyan='\x1B[1;36m';
color_white='\x1B[1;37m';

if [ "$color" = "color_none" ]; then
	c=""
	r=""
else
	c=${!color}
	r=$color_reset
fi
if [ "$error_color" = "color_none" ]; then
	ec=""
	er=""
else
	ec=${!error_color}
	er=$color_reset
fi

prefix=`printf "$c%-${prefix_width}s|$r" "$raw_prefix" | sed -e 's/[\\/&]/\\\\&/g'`
error_prefix=`printf "$ec%-${prefix_width}s*$er" "$raw_prefix" | sed -e 's/[\\/&]/\\\\&/g'`
"$@" 2> >(sed "s/^/$error_prefix /g" > /dev/stderr) > >(sed "s/^/$prefix /g")