[mturmon]

Right, you can use this to easily find the number of days in an arbitrary month in a script:

  % cal 2 1972 | tail +3 | wc -w
      29

[parennoob]

tail: cannot open +3 for reading: No such file or directory

What am I doing wrong?

This worked like a charm though:

cal dec 2002 | tail -6 | wc -w

(since it always takes up 6 lines, even sep 1752)

[jbarber]

The "+n" syntax is not standards compliant, from the tail info page (on fedora 19):

  On older systems, the leading '-' can be replaced by '+' in the obsolete option syntax with the same meaning as in counts, and obsolete usage overrides normal usage when the two conflict.  This obsolete behavior can be enabled or disabled with the '_POSIX2_VERSION' environment variable (*note Standards conformance::).

[typicalrunt]

It might be system-dependent. I'm on OSX and the command works properly.