$ perle 'my $x = "123"; $x =~ /(1)/; say $1'
1
$ perle 'my $x = "123"; $x =~ /(1)/; say $1 if $x =~ /2/'
Use of uninitialized value $1 in say at -e line 1.

$ perle 'my $x = "123"; $x =~ /(1)/; my $y = $1; say $y'
1
$ perle 'my $x = "123"; $x =~ /(1)/; my $y = $1; say $y if $x =~ /2/'
1