Perl Debugged

10.3. But What Did It Mean?

The following program is designed to reprint its input lines prefixed with an increasing date that skips weekends:

#!/usr/bin/perl -w
use strict;
use Time::Local;
my $t = timelocal(0,0,0,31,11,99);   # Dec 31 1999
while (<>)
   {
   my ($m, $d, $y) = (localtime $t)[4,3,5];
   $y %= 100;
   $m++;
   print "$m/$d/$y $_";
   dp { $t += 86400 } while (localtime $t)[6] == 0
                         || (localtime $t)[6] == 6;
   }

However, the output shows a date that doesn't change:

12/31/99 This is the first line
12/31/99 This is the second line
12/31/99 This is the third line

Running under the debugger won't reveal anything other than the fact that $t isn't being increased in the do block.

Wait a minute. It doesn't say do, does it? It's a typo: dp. Yes, we could ...