Draw a BCD Binary clock

Ruby, 107 103 99 94 90 characters

$><<[$/,(gets||Time.now.to_s[11,8]).tr(z=" .':","").bytes.map{|a|$><<z[a/4-12];z[a%4]}]*""

Note that the input shouldn't contain a linebreak, so to test the solution use something like echo -n "01:08:01" | ruby1.9 bcd.rb.

To test the default behavior, run it with ruby1.9 bcd.rb and enter ^D (i.e. a literal EOF).

"#{`date`}"10>+9<" .':":S-.{4/12-S=}%n@{4%S=}%

You can replace `date` with Time.now if necessary (+2 chars).

Since I did not create an implementation when writing the task I feel myself eligible to golf it from the start, too :-)

-join" .':
"[(($d="$(date)$args"[-8..-1]-ne58)|%{($_-band12)/4})+,4+($d|%{$_%4})]

History:

2011-02-26 23:50 (119) First attempt.
2011-02-26 23:55 (108) Inlining fun.
2011-02-27 00:03 (102) Optimized selecting the first line. [Math]::Floor is waaaayy too long. I hate that.
2011-02-27 02:22 (101) I don't need : for the first line.
2011-02-27 02:53 (95) Optimized getting input or current time.
2011-03-04 20:36 (88) Only a single join remains. Indexing every character needed (including the line break) from a single string.
2011-03-04 20:39 (83) Using 58 instead of : which auto-casts to integer as well – no more need to enclose $_ in quotes :-)
2011-03-04 20:42 (81) The parentheses after the -join are no longer necessary.