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Is there a reliable way to check how many colors my terminal emulator supports?

If echo $TERM prints xterm, does that unequivocally tell me how many colors my terminal emulator supports? How could I check this information reliably?

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See also: unix.stackexchange.com/questions/9957/… – jasonwryan Nov 1 '11 at 17:34

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The value of $TERM does not give much information about the number of supported colors. Many terminals advertise themselves as xterm, and they can support any number of colors from just 2 to at least 256.

You can query the value of each color with the OSC 4 ; c ; ? BEL control sequence. If the color number c is supported, the terminal will answer back with the value of the color. If the color number is not supported, the terminal answers nothing. Here's a bash/zsh snippet to query whether color 42 is supported (redirect to/from the terminal if necessary):

printf '\e]4;%d;?\a' 42
if read -d $'\a' -s -t 1; then … # color 42 is supported

I don't know of a more direct way.

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Thanks @Gilles. This looks great. May I ask what read -d $'\a' -s -t 1 does? – user815423426 Nov 1 '11 at 22:50
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@intrpc Read input until the first \a (bell character), without echoing input, with a timeout of 1 second. – Gilles Nov 1 '11 at 22:55
The result on my terminal (color 42 is supported) is inconsistent with tput colors, which returned 8. What gives? – l0b0 Nov 2 '11 at 8:44
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@l0b0 tput colors queries the terminfo database. Chances are that you have TERM=xterm. Xterm can support at least 2, 8, 16, 88 or 256 colors depending on the version and on compile- and run-time options, but the terminfo database can only store one value. You can set e.g. TERM=xterm+256color, but then you'll be annoyed when you log in to a machine that doesn't have this entry in its termcap/terminfo database. – Gilles Nov 2 '11 at 11:59
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@l0b0 Your pipe obviously has nothing to do with the terminal. You need to print to the terminal (printf … >/dev/tty) and then read from the terminal (read … </dev/tty). Xterm responds to the OSC 4; …; ? BEL sequence by injecting keystrokes. – Gilles Feb 24 '12 at 15:01
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There is a perl script, 256colors2.pl, that will display all the colours on your terminal.

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