coloring in heredocs, bash

Question

If I have previously defined color variable like this:

txtred='\e[1;31m'

How would I use it in heredoc:

    cat << EOM

    [colorcode here] USAGE:

EOM

I mean what should I write in place of [colorcode here] to render that USAGE text red? ${txtred} won't work, as that is what I am using throughout my bash script, outside of heredoc

score 12 · Accepted Answer · edited Mar 03 '18 at 03:15

12

You need something to interpret the escape sequence which cat won't do. This is why you need echo -e instead of just echo to make it work normally.

cat << EOM
$(echo -e "${txtred} USAGE:")
EOM

works

but you could also not use escape sequences by using textred=$(tput setaf 1) and then just use the variable directly.

textred=$(tput setaf 1)

cat <<EOM
${textred}USAGE:
EOM

edited Mar 03 '18 at 03:15

Roko C. Buljan

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answered Jul 11 '14 at 15:29

Etan Reisner

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Great. Is there a way to preserve formatting, because right know as it is, it moves `USAGE` text to the right? – branquito Jul 11 '14 at 15:35
Sorry it does not now, when I use `${tr}` instead of `$tr`. It was because of space I needed to insert beetween `$tr` and `USAGE`. – branquito Jul 11 '14 at 15:36
This is a great answer! Although, I replaced `tput` with `echo` because I couldn't find a `tput` command for reset. so `txtred=$(echo "\e[1;31m")` and `reset=$(echo "\e[0m")`. Although, if you're really into `tput` I think [this will be really helpful](https://unix.stackexchange.com/questions/269077/tput-setaf-color-table-how-to-determine-color-codes) – Justin Wrobel Aug 03 '21 at 15:17

bxm · Answer 2 · 2020-05-07T09:52:41.240

Late to the party, but another solution is to echo -e the entire heredoc block via command substitution:

txtred='\e[1;31m'

echo -e "$(
cat << EOM
${txtred} USAGE:
EOM
)" # this must not be on the EOM line

NB: the closing )" must fall on a new line, or it'll break the heredoc end marker.

This option might be appropriate if you have a lot of colours to use and don't want a lot of subshells to set each of them up, or you already have your escape codes defined somewhere and don't want to reinvent the wheel.

coloring in heredocs, bash

2 Answers2