[Boston.pm] Non-matching regexp doesn't set $1 to undef. Should it?

[Ron Newman]

If I try to match a regular expression that contains parentheses, and 
the match fails, shouldn't $1 be set to undef rather than keeping 
whatever value it had before?   The following program demonstrates what 
looks to me like very strange behavior.   Adding "local $1 = undef;" in 
the position shown did not change this behavior.

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

sub1("There are 100 words.");

sub sub1 {
  my $s = shift;
  $s =~ /There are (\d+) words./;
  print "sub1 (before call): \$1=$1\n";
  sub2($s);
  print "sub1 (after call): \$1=$1\n";
}
sub sub2 {
  my $s = shift;
  # local $1 = undef;  <--- Adding this has no apparent effect.
  print "sub2 (before match): \$1=$1\n";
  $s =~ /There are ([a-z]+) words./;
  print "sub2 (after match): \$1=$1\n";
  }
------------------
The output:
sub1 (before call): $1=100
sub2 (before match): $1=100
sub2 (after match): $1=100
sub1 (after call): $1=100
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