I have defined the color red using tput
red=$(tput setaf 1)
to colorize warnings in my program. This works fine:
printf '%sfail\n' "$red"
# prints 'fail' in red
But on one occasion I would like to print out the escape sequence as-is, something like:
\E[31mfail
How would I do this? I know printf has a %q flag but it escape others stuff I don't want to.
Sounds like you want the opposite of printing them literally, you want those escape characters converted to a printable descriptive form like \E or \033, ^[...
If it's just the ESC (0x1b) character you want to convert to \E, then with ksh93, zsh or bash (typically, the same ones that also support that non-standard %q), you can do:
printf '%s\n' "${red//$'\e'/\\E}"
Or pipe to sed $'s/\e/\\\\E/g'
For a more generic approach at converting non-graphical characters, you can use:
$ printf %s "$red" | od -A n -vt c # POSIX
033 [ 3 1 m
$ printf %s "$red" | sed -n l # POSIX
\033[31m$
$ printf '%s\n' "${(qqqq)red}" # zsh
$'\033[31m'
$ printf '%s\n' "$red" | cat -vt # some cat implementations
^[[31m
$ printf %s "$red" | uconv -x ':: [:Cc:]; ::Hex;' # ICU tools
\u001B[31m
$ printf %s "$red" | uconv -x ':: [:Cc:]; ::Name;' # ICU tools
\N{<control-001B>}[31m
Use od, hexdump, xxd, or similar to print binary data in human-readable form. For example:
$ tput setaf 1 | od -c
0000000 033 [ 3 1 m
0000005
You can use printf directly, eg
printf "\033[31mfail"
\E, or other control characters?