Recipe 15.5 Changing Text Color

15.5.1 Problem

You want text to appear in different colors on the screen. For instance, you want to emphasize a mode line or highlight an error message.

15.5.2 Solution

Use the CPAN module Term::ANSIColor to send the ANSI color-change sequences to the user's terminal:

use Term::ANSIColor;

print color("red"), "Danger, Will Robinson!\n", color("reset");
print "This is just normal text.\n";
print colored("<BLINK>Do you hurt yet?</BLINK>", "blink");

Or, you can use convenience functions from Term::ANSIColor:

use Term::ANSIColor qw(:constants);

print RED, "Danger, Will Robinson!\n", RESET;

15.5.3 Discussion

Term::ANSIColor prepares escape sequences that some (but far from all) terminals will recognize. For example, if you normally launch a color-xterm, this recipe will work. If you normally use the normal xterm program, or have a vt100 in your kitchen, it won't.

There are two ways of using the module: either by calling the exported functions color($attribute) and colored($text, $attribute), or by using convenience functions like BOLD, BLUE, and RESET.

Attributes can be a combination of colors and controls. The colors are black, red, green, yellow, blue, magenta, on_black, on_red, on_green, on_yellow, on_blue, on_magenta, on_cyan, and on_white. (Apparently orange and purple don't matter.) The controls are clear, reset, bold, underline, underscore, blink, reverse, and concealed. clear and reset are synonyms, as are underline and underscore. reset restores the colors to the way they were when the program started, and concealed makes foreground and background colors the same.

You can combine attributes:

# rhyme for the deadly coral snake
print color("red on_black"),  "venom lack\n";
print color("red on_yellow"), "kill that fellow\n";

print color("green on_cyan blink"), "garish!\n";
print color("reset");

We could have written this as:

print colored("venom lack\n", "red", on_black");
print colored("kill that fellow\n", "red", "on_yellow");

print colored("garish!\n", "green", "on_cyan", "blink");

or as:

use Term::ANSIColor qw(:constants);

print BLACK, ON_WHITE, "black on white\n";
print WHITE, ON_BLACK, "white on black\n";
print GREEN, ON_CYAN, BLINK, "garish!\n";
print RESET;

Here, BLACK is a function exported from Term::ANSIColor.

It's important to print RESET or color("reset") at the end of your program if you're not calling colored for everything. Failure to reset your terminal will leave it displaying odd colors. You may want to use:

END { print color("reset") }

to ensure the colors will be reset when your program finishes.

Attributes that span lines of text can confuse some programs or devices. If this becomes a problem, either manually set the attributes at the start of each line, or use colored after setting the variable $Term::ANSIColor::EACHLINE to the line terminator:

$Term::ANSIColor::EACHLINE = $/;
print colored(<< EOF, RED, ON_WHITE, BOLD, BLINK);
This way
each line
has its own
attribute set.
EOF

15.5.4 See Also

The documentation for the Term::AnsiColor module from CPAN