How to color terminal output with variable name in another variable-CodePudding

So I want to color my terminal output but nothing works for me. I have script with code and txt file which I read input from. It looks something like this:

example.txt

                                    ${BLUE}_.
                            _/=\:<
                          .#/*${RED}let}
                        //as\@#:~/
                       try()|:-./
                      ${BLUE}*~let${RED}:>${BLUE}@{#
                      </>}#@~*/
                     ${RED}( !:~/ /
                     /={ |
-

script.sh

BLUE="\033[0;34m"
RED="\033[0;31m"
while IFS= read -r line
do
    # print colored line
done < example.txt

It works with hardcoded code in print function but while reading the variable from txt file it doesn't. This works fine:

printf '%b\n' "$BLUE$line"

or this

printf '%b\n' "\033[0;34m$line"

and this

printf '\033[0;34m%s\n' "$line"

but this doesn't:

printf '%b\n' "$line"
# shows ${BLUE} and the rest of the string
# instead of colored output

Is it possible or do I have to change variables in txt file to colors like this:

\033[0;34mSample text
and \033[0;31Sample text.

CodePudding user response：

Very simply as:

BLUE=$'\033[0;34m' RED=$'\033[0;31m' envsubst < example.txt

By having the ANSI sequences directly in the environment variables, rather than escape codes, this relieves the need to um-escape the whole file content. ANSI sequences are already encoded.

Now, a more portable approach would be, to get the actual sequences from tput commands, rather than hard-coded ANSI.

BLUE=$(tput setaf 4) RED=$(tput setaf 1) envsubst < example.txt

CodePudding user response：

With bash and envsubst:

export BLUE="\033[0;34m"
export RED="\033[0;31m"
printf "%b\n" "$(envsubst <example.txt)"

See: man envsubst