Highlight any help text in the stdin.

colorize_help

# Highlight any help text in the stdin.
# It has been tested with various command line tools and should be able to handle most
# of them regardless of the language or framework used to write them.
#
# Since this is just a sed pattern, it works in any shell. For example, in my zsh setup
# I have a global alias
#
#   export LESS=-FR  # enable colors, exit if contents fit in one screen
#   alias -g h='--help |& colorize_help | less'
#
# This way, simply appending 'h' to a command shows me its highlighted, readable help text.
# Since it runs sed a single time, it does not add much overhead. On my system, it adds
# around 1-5ms.
#
# Author: Sarunas Nejus, 2020
# License: MIT

R=$'\033[0m'
B=$'\033[1m'
RB=$'\033[22m' # reset bold

BRED=$'\033[1;31m'
BGREEN=$'\033[1;32m'
BYELLOW=$'\033[1;33m'
BBLUE=$'\033[1;34m'
BMAGENTA=$'\033[1;35m'
BCYAN=$'\033[1;36m'
BGREY=$'\033[1;38;5;239m'
BINVGREY=$'\033[1;30;48;5;243m'


colorize_help() {
  # args:
  # info: colorize help text in the stdin
  sed -r '
    # remove any previous ansi colors
    s/(.(\[[0-9][^ m]*m)+)//g
    # everything within single quotes in blue
    s/ ('\''[^'\'']+'\'')/ '"$BBLUE\1$R"'/g

    # memorize current line
    h
    {
      # remove comment
      s/ -- .*//

      ### Required arguments
      # -f arg / -f ARG
      s/((^|[[ ]-)\w\b )(\w(\w|-)*\b)(\W\B|$)/\1'"$BMAGENTA\3$R"'\5/g
      # --flag=arg / --flag=ARG
      s/((^|[[ ]--)(\w|-)+\b=)(\w(\w|-)*\b)(\W\B|$)/\1'"$BMAGENTA\4$R"'\6/g
      # Within <>
      s/<([^>…]+)>/'"$MAGENTA<$BMAGENTA\1$RB>$R"'/g
      # Capitalized
      /^[A-Z -]+$/!{  # skip lines that only have capitalized words
        /([( ])(\$?\b[A-Z][-_A-Z0-9/]+)(\b[^:]|$)/s//\1'"$BMAGENTA\2$R"'\3/g
      }

      ### Flags (optional)
      # -f | --flag | --[no-]flag
      s/(^|[[( ])((-?-((\w|\b-)+\b|\[(\w|[=-])+\])+ ?)+)([^}]|$)/\1'"$BYELLOW\2$R"'\7/g
      # ...
      s/\.{3}/'"$BYELLOW&$R"'/g
      # [=?argument] or [=?ARGUMENT]
      s/([ =])\[(=?([a-z)(-]+|[A-Z)(-]+))\]/\1['"$BYELLOW\2$R"']/g

      ### Commands
      # Usage: create
      /([Uu]sage: )([-a-z_]+)/s//\1'"$BBLUE\2$R"'/g
      # ^   create  ......
      /^(  {,10})(([a-z0-9,_-]|\.\w)+)([ \t]{2,}| *$)/s//\1'"$BCYAN\2$R"'\4/

      ### Default values
      # =arg|=ARG
      /[A-Z]+:/s//'"$BGREEN&$R"'/g

      ### Specific values / arguments
      # {arg,...}
      /\{[^}]+\}/{
        s//'"$BGREEN&$R"'/
        s/,/'"$R,$BGREEN"'/g
      }
      # arg|other-arg
      /((\w|-)+\|)+(\w|-)+/{
        s//'"$BGREEN&$R"'/g
        s/\|/'"$R|$BGREEN"'/g
      }

      ### Punctuation
      s/([^[:cntrl:]a-z-]|0m)\[/\1'"$YELLOW\[$R"'/g
      s/(\]+)([^]a-z]|$)/'"$YELLOW\1$R"'\2/g

      ### Group title
      /^[A-Z -][^[:cntrl:]a-z]+$/{
        /^([A-Z][^,|<]+)$/s//'"$BINVGREY & $R"'/
        /^  # [A-Za-z]/d
      }
    }

    ### Comments
    {
      # swap/memorise the non-comment bit processed above with the initial/memorised line
      x
      # remove non-comment bit and color the comment
      /.* -- (.*)/{
        /.*[^ ].* -- (.*)/s//'"$BGREY-- \1$R"'/
        /[ ]+ -- (.*)/s//'"$BGREY   \1$R"'/
        # if comment was not found, remove the duplicate command
        s/  [a-z]+ *$//
        # color keywords
        s/([ (])_([^ ]+)/\1'"$BBLUE\2$BGREY"'/g
        s/$/'"$R"'/
        # append it to the memorised non-comment bit
        H
      }
    }
    # retrieve the entire thing and join it
    x; s/\n//
  '
}
# vim: ft=zsh

Examples

sed

grep

bat (Rust)

yay (Go)

pip (Python)

git-merge(1) manual