How do I determine if a terminal is color-capable?

Question

I would like to change a program to automatically detect whether a terminal is color-capable or not, so when I run said program from within a non-color capable terminal (say

Answer 1

Look up the terminfo(5) entry for the terminal type and check the Co (max_colors) entry. That's how many colors the terminal supports.

Answer 2

A friend pointed me towards tput(1), and I cooked up this solution:

#!/bin/sh

# ack-wrapper - use tput to try and detect whether the terminal is
#               color-capable, and call ack-grep accordingly.

OPTION='--nocolor'

COLORS=$(tput colors 2> /dev/null)
if [ $? = 0 ] && [ $COLORS -gt 2 ]; then
    OPTION=''
fi

exec ack-grep $OPTION "$@"

which works for me. It would be great if I had a way to integrate it into ack, though.

Answer 3

You almost had it, except that you need to use the lower-level curses function setupterm instead of initscr. setupterm just performs enough initialization to read terminfo data, and if you pass in a pointer to an error result value (the last argument) it will return an error value instead of emitting error messages and exiting (the default behavior for initscr).

#include <stdlib.h>
#include <curses.h>

int main(void) {
  char *term = getenv("TERM");

  int erret = 0;
  if (setupterm(NULL, 1, &erret) == ERR) {
    char *errmsg = "unknown error";
    switch (erret) {
    case 1: errmsg = "terminal is hardcopy, cannot be used for curses applications"; break;
    case 0: errmsg = "terminal could not be found, or not enough information for curses applications"; break;
    case -1: errmsg = "terminfo entry could not be found"; break;
    }
    printf("Color support for terminal \"%s\" unknown (error %d: %s).\n", term, erret, errmsg);
    exit(1);
  }

  bool colors = has_colors();

  printf("Terminal \"%s\" %s colors.\n", term, colors ? "has" : "does not have");

  return 0;
}

Additional information about using setupterm is available in the curs_terminfo(3X) man page (x-man-page://3x/curs_terminfo) and Writing Programs with NCURSES.