How would I go about colorizing the output of tail with sed?
echo "`tput setaf 1`foo`tput op`" works as expected
echo "foo" | sed -e 's/(foo)/`tput setaf 1`\0`tput op`/g' however, does not.
What am I missing here?
2 Answers
The backticks `` in the echo command spawn a process and it's output is substituted into the echo command line. You can see this with e.g.
echo "`tput setaf 1`" | hexdump -C
00000000 1b 5b 33 31 6d 0a |.[31m.|
This works because the contents of the "..." are expanded before being passed to echo.
The sed command you're using wraps everything in ' so it is passed to sed without expansion and sed sees it all as literal text.
You can fix this by putting "" around your sed command
echo "foo" | sed -e "s/\(foo\)/`tput setaf 1`\1`tput op`/g"
You also had an error in your sed command. The ( and ) need to be escaped \( and \) to denote the remembered pattern. I've also never use \0 I've always used \1 as the first remembered pattern.
Does it have to be sed?
echo "foo bar baz" | grep --color=auto "bar"
The above will highlight bar in red by default. The man page says you can choose what colour to use with the environment variable GREP_COLORS.
To make it print all lines and only highlight bar:
echo "foo bar baz" | grep -E --color=auto "^|bar"
-
1+1 use the right tool for the job - there is no need to rape sed just to colorize output.– syneticon-djNov 23, 2012 at 20:41
-
@syneticon-dj: This doesn't actually work to colour the output of tail though. It will only print lines containing "bar" (with bar highlighted) and all other lines will be left unprinted.– user591Nov 23, 2012 at 20:45
-
@Iain adding
-C <great number>should help as a quick hack– syneticon-djNov 23, 2012 at 22:52 -
Not worth a whole new answer, but you can also just do:
tail file | grep "pattern\|"ortail file | grep -E "pattern|", depending on your mood. ;) (Supposing you already have--color=autoin yourCOLOR_OPTIONSenvironment variable set)– DrBecoNov 20, 2017 at 3:43
grepdoes not.