I have no idea what a $yday is!
If you just need some tokens from this line like day and year:

#!/usr/bin/perl -w
use strict;

my $string= "Wednesday, May 20, 2009 2:09 PM";

my ($day, $year) = (my @tokens = split(/[,\s]+/,$string))[0,3];

print "@tokens \n";
print "day =$day  year =$year\n";
__END__
PRINTS:
Wednesday May 20 2009 2:09 PM 
day =Wednesday  year =2009
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Update: I'll add a bit more for you...split() is a function that parses a scalar value (here its just one line) and creates a list. In this case we "split" on any sequence of one (or more) comma's or space characters (\n\t\r\s\f). These go into the @tokens list. Perl has a very cool syntax called a "list slice", here I say give the first and fourth things which are the day and the year. "my @tokens =" is an intermediate variable that doesn't need to exist, I put it there so you could see the effect of the split.

Give some examples of what need...short thing with couple of input lines and couple of output lines.