title: Fish shell custom function for output text coloring
body: <p>When using fish shell in a terminal-emulator (such as terminator) together with a command that outputs lots of text it could be useful to get some color coding on the output. I know that a script can add color code information to the output like "<em>grep --color=auto</em>". I guess it's possible to modify the fish terminal to scan through the output and add this in special places?</p>
  
  <p>What I want to do is that the text "error" appearing in the output from any script always is marked red and that "warning" always is marked yellow. Anyone knows if this is possible by introducing function files in the <em>~/.config/fish/functions</em> dir or similar? </p>