How do I make `less` output colors?

Question

When I run a program (for example grep or ls) without a pager, its output is colored. However when I run it piping its output to less, no colors are shown.

For example, this command outputs colored output:

grep -r something

but this doesn't:

grep -r something | less

Why? How can I see colors through less?

Solution 1

There are two problems here:

• Commands like ls —which auto-detect the colour support— don't find support from pipes
• less is set to just display colour codes by default.

Both can be overcome but it's a bit clunky:

ls --color=always | less -R

This isn't ls specific. Many commands that support colour also have an override argument.

---

A slightly more in-depth answer is that ls is checking whether or not its STDOUT belongs to a real terminal or not. When you pipe things around, the STDOUT is set to the STDIN of the next command.

You can see this at work in the ls source code. It's using the isatty command (a core POSIX interface) to work out what the situation is:

• Are colours on by default:

      print_with_color = (i == color_always
                          || (i == color_if_tty
                              && isatty (STDOUT_FILENO)));
  

• Do we try to output in multiple columns:

  if (format == long_format)
    format = (isatty (STDOUT_FILENO) ? many_per_line : one_per_line);
  
  //...
  
  if (isatty (STDOUT_FILENO))
    {
      format = many_per_line;
      set_quoting_style (NULL, shell_escape_quoting_style);
      qmark_funny_chars = true;
    }
  else
    {
      format = one_per_line;
      qmark_funny_chars = false;
    }
  

grep does a very similar thing, unless explicitly overridden, it'll detect colour support, with isatty:

color_option = isatty (STDOUT_FILENO) && should_colorize ();

Solution 2

If you're interested in colors in less more generally, you might want to look at lesspipe.sh. See, for example, https://github.com/wofr06/lesspipe.

lesspipe.sh is an input filter for the pager less as described in less's man page. The script runs under a ksh-compatible shell (e.g. bash, zsh) and allows you to use less to view files with binary content, compressed files, archives, and files contained in archives.

It will also colorize shell scripts, perl scripts, etc. similarly to a text editor, but without the use of any "preprocessing" program to do the colorizing.

Comments

[Rinzwind]

grep --color=always "search string" * | less -R but I tend to use most nowadays instead of less. ALSO: gnu.org/software/src-highlite is a color highlighter (less works too)

[sourav c.]

@alex have you installed python-pygments?

[Mohammad Reza Rezwani]

@souravc no I did not install that

[Rinzwind]

@ales ignoring me are we? >:-D

[Pablo Bianchi]

Check here (or here) if what you want is just syntax highlight on less

[hytromo]

My last upvote (reached the limit) for today to support you for 100k. But me and Rinzwind want cake when that happens.

[Oli]

@alex ack has a --color argument: ack-grep -i select --color | less -R

[Mohammad Reza Rezwani]

@Oli .........Oh my God........ the only thing that I can say about your knowledge and help and also power of linux

[Rinzwind]

@ales he stole that line from my comment >:-D

[Oli]

@Rinzwind I'd like to say "BWAHAHAAA!" but I didn't even notice :(

[Rinzwind]

@oli ok but hakermania and me want cake in 1900 rep >:D

[Braden Best]

I still wonder how ls does its output. Not the colors, I'm talking how it displays the files in columns to optimally fill the whole width of the terminal, and then the second you pipe it to something, it's a straight list. That's some ingenious engineering.

[Oli]

@B1KMusic I agree. I agree so much that I found how how it works and updated the answer. You can force columns with a -C argument.

[vstepaniuk]

For me it doesn't work: printf "a\nb\n" > text; pcregrep -M --color=always "a\nb\n" text | less -R highlights only "a", but should both "a" and "b".