Just a note: you can test whether @ARGV has any members with the idiomatic

my $date;
if (@ARGV) {
   $date = $ARGV[0];
}
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Two things: @ARGV gets evaluated in a scalar context, which means that what is checked is the *number* of elements in the array; if that number is *not* 0 (i.e. if there are any elements in the array), the test evaluates to true, and the block will be executed.

Second note : the *declaration* of $date occurs outside the braces, so when you set $date inside the braces, that change will be visible to other code outside the braces. When you use my inside a set of braces, you're creating a *new* variable that is only visible to code inside the braces. You can see how this works with

my $date = "bar"; 
print "Outside 1 : $date\n";
{ 
     my $date = "foo"; 
     print "Inside : $date\n";
}
print "Outside 2 : $date\n";
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Incidentally, you can make your $date setting very compact by using || or the "ternary operator" (see perlop):

my $date = $ARGV[0] || yesterday();

sub yesterday {
    my ($yr,$mo,$day) = (localtime( time - 86400 ))[5,4,3];
    return sprintf "%04d%02d%02d",1900+$yr,1+$mo,$day;
}
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if $ARGV[0] evaluates to false ( because it doesn't exist, or was 0 ), then $date gets set to what the yesterday sub returns.

HTH. /msg me if you need anything explained.

perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n"; *other_name = *rose; print "$oth
+er_name\n"'
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