this post was submitted on 20 Jan 2025
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retain terminal output colors through piped commands? (discuss.tchncs.de)
submitted 1 week ago by linuxPIPEpower@discuss.tchncs.de to c/linux@lemmy.ml
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Is there anyway to pass terminal colors through a pipe?

As a simple example, ls -l --color=always | grep ii.

When you just run the ls -l --color=always part alone, you get the filenames color coded. But adding grep ii removes the color coding and just has the grep match highlighting.

Screenshot of both examples:

In the above example I would want ii.mp3 and ii.png filenames to retain the cyan and magenta highlighting, respectively. With or without the grep match highlighting.

Question is not specific to ls or grep.

If this is possible, is there a correct term/name for it? I am unable to locate anything.

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[–] shiny_idea@aussie.zone 11 points 1 week ago

Color codes will pass through pipes just like any other output.

In this case, your grep is being smarter than you want and actually parsing the incoming color codes itself.

You can try a simpler program like head, tail, or even sed -n /ii/p to see it for yourself.

You can also control GNU grep's color processing with --color but you may not find exactly what you seek.

[–] eager_eagle@lemmy.world 8 points 1 week ago* (last edited 1 week ago) (1 children)

hmm this gives me all colors (from ls and grep)

/usr/bin/ls -l --color=always | /usr/bin/grep --color=always a

(I'm using their full paths because I usually alias ls and grep to eza and rg respectively)

There's a export CLICOLOR_FORCE=1 you can try to avoid repeating --color=always, but that didn't work for me with ls and grep specifically.

Edit: there's also a FORCE_COLOR=1 that is popular, but again, neither ls nor grep seem to care.

[–] oshu@lemmy.world 2 points 1 week ago

hot tip, you can avoid the ls alias by running \ls

[–] Max_P@lemmy.max-p.me 3 points 1 week ago* (last edited 1 week ago)

For the most part, this happens because those programs check if stdout is a pseudo-terminal (pty) and automatically disable color output because if you're doing say ls -l and try to parse it, you'll have all the ANSI escape sequences mixed in, so for safety and predictability they disable color.

It is unfortunately a per-program thing. It is possible to fake it using script or unbuffer according to https://stackoverflow.com/a/32981392

Looks like socat can also be used for that: https://unix.stackexchange.com/a/157463

[–] vk6flab@lemmy.radio 2 points 1 week ago

TL;DR - Essentially you're attempting to mix two types of output, a pipe with a terminal. This is pretty much not going to work as expected.

To make colour in a terminal, commands like ls add so-called Escape sequences, a series of bytes that your terminal knows how to interpret as colour.

Whilst you might be able to force those characters though a pipe, they're just characters, so if you only grab part of those characters, you'll create invalid Escape sequences and all hell will break loose, exactly like what happens if you run cat on a binary file and the terminal display goes haywire. You can often recover using the reset command.

This is why programs like ls and grep detect if they're running as a terminal command or a pipe command and suppress the Escape sequences when you are sending their output to anything other than a terminal.