The GCD of 3 and 5 is 10
-- main::(gcd.pl:18)
die sprintf "Need two integer arguments, got %d", scalar(@ARGV) unless 
    @ARGV == 2;
--> #0 file `gcd.pl' at line 18
x1 main::(gcd.pl:9)
    my ($a, $b) = @_;
--> #0 @ = main::gcd(3, 5) in file `gcd.pl' at line 9
    #1 file `gcd.pl' at line 21
Breakpoint 2 set in 14 at line 14
xx main::(gcd.pl:14)
    return $a if ($a == 1) or ($b-$a == 0);
--> #0 @ = main::gcd(1, 2) in file `gcd.pl' at line 14
    #1 @ = main::gcd(2, 3) in file `gcd.pl' at line 15
    #2 @ = main::gcd(3, 5) in file `gcd.pl' at line 15
    #3 file `gcd.pl' at line 21
<- main::(gcd.pl:15) main::gcd
    return gcd($b-$a, $a);
Return array value for main::gcd is:
1

Return array value set to:
10