a soft sea

Have you ever wondered how some command line programs add artistically horrid colors to textual output? Ever wonder why you might see an ls listing showing directories in yellow or soft-linked files in red on some machine terminals and not others. I love colors as much as anyone else does, so I’m curious too.

Well, back in the days before we had a style markup language for designers we had programmers design a style markup language for… programmers. Some OS’s may vary but basically the magic seeps from an environment variable called LSCOLORS and the ls command line flag --color or another environment variable called CLICOLOR.

Back in those arcane days we didn’t have any of these fancy pants style sheets so the best we could come up with was the following approach.

First, define a set of finite codes that indicate which ANSI colors are available.

Then define an indexing for types of file listings based foreground+background pairings

The result of which being something like

export LSCOLORS=dxfxcxdxbxegedabagacad

Pretty obvious and easy to read huh?

The other day I was playing around with Scala’s REPL and came across something new. By now I should hope we all know about Scala’s Predef object. Where else do you think all of those implicit conversions are coming from? Ohio? Referenced inside Predef is one neat little class that’s easy to look right past: Console. Console provides us with some wildly fun library methods like println and readLine. What fun right?

So what’s Console got to do with color? Everything.

One of the newer features of Scala’s REPL is method tab completion. I see some irb users in the back yawning so I’ll get to my point. One of the useful side effects of having tab completion is api discovery. Guess what I get if I crack open a Scala REPL and type

scala> Console.<tab>

BLACK          BLACK_B        BLINK          BLUE           BLUE_B         BOLD           CYAN
CYAN_B         GREEN          GREEN_B        INVISIBLE      MAGENTA        MAGENTA_B      RED
RED_B          RESET          REVERSED       UNDERLINED     WHITE          WHITE_B        YELLOW
YELLOW_B       asInstanceOf   err            flush          in             isInstanceOf   out
print          printf         println        readBoolean    readByte       readChar       readDouble
readFloat      readInt        readLine       readLong       readShort      readf          readf1
readf2         readf3         setErr         setIn          setOut         toString       withErr
withIn         withOut

Hrm… What’s this?

What are all these values named after ANSI colors doing in Console’s pantry?

What you will find is that Console has provided functions values for colorizing… your console’s output. What can we do with this? Colorize your CLI’s interface and make it all pretty like. The convention is Console.{COLOR} for setting foreground colors and Console.{COLOR}_B for setting background colors. Pretty sweet.

So in your REPL you can type

scala> Console.MAGENTA_B

Which will turn your terminals background to a nice shade of magenta.

Then add a tasteful green foreground with

scala> Console.GREEN

You should see some thing like

scala> “colors” :: “are” :: “awesome” :: Nil mkString(” “)

But wait there’s more. There’s BLINK! Your remember <blink></blink> don’t you?

So does Scala

scala> Console.BLINK

and behold

scala> “colors” :: “are” :: “awesome” :: Nil mkString(” “)

Don’t worry. You can always revert these changes to console output with Console.RESET.

Optionally, if you are feeling like a coding ninja I’d recommend Console.INVISIBLE

These are the things I live for.