Colored grep output getting fragmented by watch command

colorsgrepwatch

I'm trying to run watch, so that it shows me the output from my grep command, while I am running over files and changing things.

The usual way of doing this works fine, but lacks colors:

watch grep 'something' **/*

…and since I do want colors, I did this:

watch grep 'something' **/* --color=always

It's still ugly, because watch doesn't parse the escape codes that make the colors work. So then I found this:

watch --color grep 'something' **/* --color=always

And well… it doesn't work. The output is fragmented / mixed up in some weird way. It shows me only a single line for some reason, while without watch --color the grep outputs about 20.

How can I make watch work with colorized output from grep?

Isolated case:

Using the following:

mkdir grep_test; cd grep_test
echo "asdsad\nasdasd\nsaasdasd" > file1 
echo "test\n123\ntest" > file2

I create two files, and run the following command:

grep test * --color=always

Which works as expected, and outputs (with colors and whatnot):

file2:test
file2:test

But when I use watch:

watch --color 'grep test * --color=always'

It outputs nothing. Without the --color option it shows the right output, though without the ANSI escapes interpreted.
I'm running this on Fedora 25, in tmux session with zsh inside.

Also, watch -v output is:

watch from procps-ng 3.3.10

Best Answer

It turns out that watch does work with color output. But specifically for grep you should make some workaround (according to grep --color adds ANSI code ESC[K - This can change displayed text)

watch --color "GREP_COLORS=ne grep --color=always .* *"

Related Solutions

Grep –color adds ANSI code ESC[K – This can change displayed text

You can change this behavior by setting the GREP_COLORS environment variable:

export GREP_COLORS=ne
echo -e "ab\rc" | grep --color=always "c"

From the grep man page:

          ne     Boolean  value  that prevents clearing to the end of line
                 using Erase in Line (EL) to Right  (\33[K)  each  time  a
                 colorized  item  ends.   This  is  needed on terminals on
                 which EL is not supported.  It  is  otherwise  useful  on
                 terminals  for  which  the back_color_erase (bce) boolean
                 terminfo capability  does  not  apply,  when  the  chosen
                 highlight colors do not affect the background, or when EL
                 is too slow or causes too much flicker.  The  default  is
                 false (i.e., the capability is omitted).

It's done in the first place to set the background of the rest of the line to the correct color, in case it was changed earlier (though by default it isn't; somebody might set it up to do so in their own settings).

You may also want to play with the other options that can be set in GREP_COLORS; see the man page for full details.

Shell – Using sed to color the output from a command on solaris

\xNN is an escape sequence in GNU sed, but it is not standard, and in particular it is not available on Solaris.

You can include a literal escape character in your script, but that would make it hard to read and edit.

You can use printf to generate an escape character. It understands octal escapes, not hexadecimal.

esc=$(printf '\033')
echo "test" | sed "s,.*,${esc}[31m&${esc}[0m,"

You can call tput to generate the replacement text in the call to sed. This command looks up escape sequences in the terminfo database. In theory, using tput makes your script more portable, but in practice you're unlikely to encounter a terminal that doesn't use ANSI escape codes.

echo "test" | sed "s,.*,$(tput setaf 1)&$(tput sgr0),"

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