3

I have a multi-line string that I use for printing in a bash script.

docstring="
 Headings
  -H, -H CNT, -H=CNT, -HCNT, --heading CNT, --heading=CNT

 Warnings
  -W, -W CNT, -W=CNT, -WCNT, --warning CNT, --warning=CNT

 Errors
  -E, -E CNT, -E=CNT, -ECNT, --error CNT, --error=CNT"

echo "$docstring"

I want to make a function that takes this string and prints in colour for lines starting with - or {-.

Thus, the following will be coloured

-H, -H CNT, -H=CNT, -HCNT, --heading CNT, --heading=CNT
-W, -W CNT, -W=CNT, -WCNT, --warning CNT, --warning=CNT
-E, -E CNT, -E=CNT, -ECNT, --error CNT, --error=CNT
Improve this question

2 Answers 2

Reset to default
0

One way using GNU , assuming the strings don't contain \, `, " nor $ characters:

printred(){ 
    sed -E 's/^ *\{?-.*/tput setaf 1;printf "%s" "&";tput sgr0/e' <<< "$@"
}

Usage:

printred "$docstring"

To choose another color, check:

for i in {0..7}; do
    tput setaf "$i"
    echo "tput setaf $i"
    tput sgr0
done

Caveats:

don't use as a CGI script as-is, keep it private, because, as pointed by Stephane Chazelas, you can run arbitrary command. This is to use in a trusted environment. Or make a kind of filter to sanitize input strings

Improve this answer
14
  • A small inconvenience is that any starting whitespaces on matched lines are removed. Commented Nov 28, 2022 at 20:40
  • @Heime: fixed now Commented Nov 28, 2022 at 20:47
  • You forgot to handle watches starting with {- Commented Nov 28, 2022 at 20:51
  • @Heime: fixed too Commented Nov 28, 2022 at 20:53
  • Had to downvote. That calls one sh, two tputs, one echo (a command that can't be used for arbitrary data) for each matching line of input, and is a command injection vulnerability. Try for instance on the output of echo '$(reboot)' that e flag (a GNU extension) should really never have been introduced. Commented Nov 28, 2022 at 21:01
0

With the GNU implementation of grep or compatible:

grep --color -Ee '^\s*\{?-.*' -e '^' <<< "$docstring"

That's grepping for lines starting with any number of whitespace character followed by an optional { followed by - followed by any number of characters, or just the start of the line, colouring what is matched as long as the output goes to a terminal device (assuming it's displayed on a terminal, the ones that interpret those escape sequences). Change to --color=always to add the colouring even when the output doesn't go to a terminal device.

What attributes and colours are used (bold red by default) is controlled via the $GREP_COLORS environment variable (formerly $GREP_COLOR).

Call grep as GREP_COLORS='mt=1;41;33' grep... for instance for the matched text to be in bold, yellow foreground, red background.

A printred function that prints the matching lines in red could then look like:

println() { # prints each of its arguments on separate lines
  [ "$#" -eq 0 ] || printf '%s\n' "$@"
}
printred() {
  println "$@" |
    GREP_COLORS='mt=31' grep --color -Ee '^\s*\{?-.*' -e '^'
}

Another way to highlight those lines without relying on GNUisms would be to used sed to add the ANSI escape sequences around matching lines with:

ESC=$(printf '\33')
printred() {
  if [ -t 1 ]; then
    println "$@" |
      sed "s/^[[:space:]]*{\{0,1\}-.*/${ESC}[31m&${ESC}[m"
  else
    println "$@"
}

Or perl instead of sed:

perl -pe 's/^\s*\{?-.*/\e[31m$&\e[m/'
Improve this answer
5
  • It is good, but want control to set with any colour, than what defined for grep. Commented Nov 28, 2022 at 20:52
  • @Heime, see edit. Commented Nov 28, 2022 at 20:57
  • I do not want to mess up grep itself. Commented Nov 28, 2022 at 21:24
  • Something like printred is preferable. Would you have a solution that also mitigates the problems you mentioned, particularly the command injection vulnerability part? Commented Nov 28, 2022 at 21:26
  • @Heime See edit. The command injection vulnerability part in Gilles' answer you could mitigate with great effort by quoting the line in sh syntax before it's passed to sh, but using that e flag is certainly the wrong approach. I've added a sed approach that doesn't have the issue as it's passing anything dynamically to programming language for it to interpret as code! Commented Nov 29, 2022 at 6:50

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.