Detect if ANSI escape codes are supported by the terminal to disable color automatically

[esaporski]

In a conversation with bluefish1432:

In CLI applications, it's usually reasonable for the app itself to decide when/how it can use ANSI color escape codes and when it can't. I wish there were an auto option for setting colors so that my logging function doesn't break a script running in CI if I forgot to manually specify "no color" for the logger

I know that a bunch of CI pipelines set CI=true, but I will do some research to check how I can detect if ANSI escape codes are supported by the terminal the script is currently running.

[jkhmtx]

tput may be relevant here, but it would introduce a dependency on ncurses in *nix

[esaporski]

At least tput is in The Open Group base specification 😁
I'll test it with Linux/BusyBox/FreeBSD/macOS.
As a proof of concept:

#!/bin/sh
# check_color.sh

NO_COLOR=true

status_code=0
output=$(tput colors 2>&1) || status_code=$?
if [ "$status_code" -eq 0 ] && [ "$output" -gt 2 ]; then NO_COLOR=false; fi

printf "NO_COLOR: '%s'\n" "$NO_COLOR"
printf "Status code: '%d'\n" "$status_code"
printf "Output: '%s'\n" "$output"

$ ./check_color.sh
> NO_COLOR: 'false'
> Status code: '0'
> Output: '256'

$ unset LS_COLORS; export TERM=vt220; ./check_color.sh
> NO_COLOR: 'true'
> Status code: '0'
> Output: '-1'