perl -wE'
"test" =~ m/(e)/; # $1 = e
foo($1);

sub foo {
    "bla" =~ m/(a)/; $1 = a
    my ($param) = @_;
    say $param;
}


my $x = 23;
bar($x);

sub bar {
    $x++;
    my ($param) = @_;
    say $param;
}
'
a
24