Man pages have colors? A deep dive into groff

Hi,

While I was doing the investigagion for my GNU_ROFF patch [1], I checked different versions of all the tools (asciidoc, asciidoctor, docbook, and groff).

When I tested my own compiled version of groff I noticed something weird: man pages have colors. This did not happen with the version shipped by Arch Linux.

I did notice the output generated by docbook stylesheets showed \m[blue], but no color showed up.

It turns out Arch Linux disables colors, and so does Debian, by disabling a feature called SGR. This happened about 10 years, and the rationale was that "it doesn't work correctly".

To enable SGR on these distributions you need to do GROFF_SGR=1, but that is not documented anywhere.

groff does check for a variable GROFF_NO_SGR, but it's the other way around: SGR is enabled unless that variable is set.

There's other ways your distribution might be screwing up with groff (for example Arch Linux converts \' to ', which is not correct), so you might want to check your shipped configuration in:

  /usr/share/groff/site-tmac/man.local

Unfortunately the colors in man pages leave a lot to be desired.

Here is a simple trick I've been using to show some custom colors:

  man() {
    GROFF_NO_SGR=1 \
    LESS_TERMCAP_md=$'\e[1;31m' \
    LESS_TERMCAP_me=$'\e[0m' \
    LESS_TERMCAP_us=$'\e[1;34m' \
    LESS_TERMCAP_ue=$'\e[0m' \
    LESS_TERMCAP_so=$'\e[1;35m' \
    LESS_TERMCAP_se=$'\e[0m' \
    command man "$@"
  }

Hopefully some of you might find this useful.

Cheers.

[1] https://lore.kernel.org/git/20210515115653.922902-2-felipe.contreras@gmail.com/