What is the scope of $1 through $9 in Perl?

Question

What is the scope of $1 through $9 in Perl? For instance, in this code:

sub bla {
    my $x = shift;
    $x =~ s/(\d*)/$1 $1/;
    return $x;    
}

my $y;

# some code that manipulates $y

$y =~ /(\w*)\s+(\w*)/;

my $z = &bla($2);
my $w = $1;

print "$1 $2\n";

What will $1 be? Will it be the first \w* from $x or the first \d* from the second \w* in $x?

Answer 1

The variables will be valid until the next time they are written to in the flow of execution.

But really, you should be using something like:

my ($match1, match2) = $var =~ /(\d+)\D(\d+)/;

Then use $match1 and $match2 instead of $1 and $2, it's much less ambiguous.

Answer 2

By making a couple of small alterations to your example code:

sub bla {
    my $x = shift;
    print "$1\n";
    $x =~ s/(\d+)/$1 $1/;
    return $x;
}
my $y = "hello world9";

# some code that manipulates $y

$y =~ /(\w*)\s+(\w*)/;

my $z = &bla($2);
my $w = $1;

print "$1 $2\n$z\n";

we get the following output:

hello
hello world9
world9 9

showing that the $1 is limited to the dynamic scope (ie the $1 assigned within bla ceases to exist at the end of that function (but the $1 assigned from the $y regex is accessible within bla until it is overwritten))