Get current terminal color pair in Perl

Question

I'm trying to learn about color text in a terminal window. (In case it matters I'm using Terminal.app on OS X.) I'd like to get the terminal's current foreground and background color pair. It looks like I should be able to get this info in a perl script using the Term::Cap library, but the solution eludes me.

In a perl script how would I query the terminal's current foreground and background color pair value?

Answer 1

The feature is outside the scope of terminfo and termcap, because it deals with terminal responses, while terminfo/termcap describe these capabilities:

• how to tell the terminal to do some commonly-implemented feature (such as clearing the screen), or
• what sequence of characters might some special key (such as Home) send from the keyboard.

While in principle, there is no limitation on what could be part of a terminal description, there was little commonality across terminals back in the 1980s for responses. A few terminals could report specific features, most of those were constant (e.g., version information). Most of the variable responses came after terminfo/termcap had more or less solidified in X/Open Curses. ncurses extends that, but again, most of the extensions are either features or special keys.

Terminal.app implements the most commonly-used features of xterm, but (like other imitators) omits most of the terminal responses. Among other things, xterm provides terminal responses which can tell an application what the window's colors are currently. There are a couple of command-line utilities (xtermset and xtermcontrol) which have been written to use this information (and again, they cover only a part of the repertoire). Using xtermcontrol demonstrates that Terminal.app is lacking in this area — see screenshot:

Answer 2

I don't think most terminals support reporting this -- and it doesn't look like termcap or terminfo have any entries for it. You're just expected to set the color pair as necessary, not to ask the terminal what it's set to right now. In the ECMA-48 standard (better known as "ANSI" after ANSI X3.64, where it used to live), the only command that makes reference to color is SGR "Set Graphic Rendition", which is purely write-only.

Answer 3

Dunno about perl or Terminal.app, but xterm etc will write foreground/background color control sequences to stdin if you output "\033]10;?\07" or "\033]11;?\07" respectively. Check out http://invisible-island.net/xterm/ctlseqs/ctlseqs.html, http://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Operating-System-Controls in particular.