Launch a program and remove bright colors from its output.

remove-bright-colors.rb

#!/usr/bin/ruby

CHILD_CMD = ARGV.dup

# If either stdout or stderr is not a TTY, executes the program with no color
# translation.

if !STDOUT.tty? or !STDERR.tty?
  exec(*CHILD_CMD)
end


# Map bright colors to the default color..

COLOR_TABLE = {
  "1"       => "0",

  "38;5;9"  => "31",
  "38;5;09" => "31",
  "38;5;10" => "32",
  "38;5;11" => "33",
  "38;5;12" => "34",
  "38;5;13" => "35",
  "38;5;14" => "36",
  "38;5;15" => "0",

  "90"      => "30",
  "91"      => "31",
  "92"      => "32",
  "93"      => "33",
  "94"      => "34",
  "95"      => "35",
  "96"      => "36",
  "97"      => "30",
}

require "pty"
require "io/console"


# Launch the program in a new TTY.

master, slave = PTY.open
master.winsize = STDOUT.winsize

pid = fork do
  STDIN.reopen("/dev/null")
  STDOUT.reopen(slave)
  STDERR.reopen(slave)
  exec(*CHILD_CMD)
end

slave.close


# Forward signals

trap "TERM" do
  Process.kill("TERM", pid)
end

trap "SIGWINCH" do
  master.winsize = STDOUT.winsize
end


# Main loop.
#
# Read up to 1024 bytes from the TTY, and replace colors (CSI color m) if they
# are found in COLOR_TABLE.
#
# If a sequence is at the end of the input it may be incomplete. In such case,
# it will not be replaced. This should be very unlikely for most CLI programs.
loop do
  begin
    line = master.
      readpartial(1024).
      gsub(/\e\[([0-9;]+?)m/) { "\e[#{COLOR_TABLE[$1] || $1}m" }

    print line

  rescue Errno::EIO
    break

  rescue Interrupt
    Process.kill("INT", pid)
    puts

  end
end

Process.waitpid(pid)
exit $?.exitstatus || 1