This has already been covered in other posts, but this may clarify things for Wassercrats.

If you don't scope your variables, it is not immediately obvious whether:
1) You variables will have changed by calling a sub.
2) If the variables did change, whether they were changed on purpose, or accidently.

$x = 0;
DoStuffX();
print "As long as no one used global variables, I know that x = 0 ",
      "without needing to know what DoStuffX does.\n";
if ($x != 0) { print "Nope, I need to spend time looking through ",
                     "DoStuffX to find out why x changed. I really ",
                     "wish the guy used \$x=DoStuffX(\$x) so that I ",
                     "would know whether he changed x intensionally ",
                     "or not.\n\n" };

$y = 0;
DoStuffY($y);
print "As long as no one used global variables, I know that y = 0 ",
      "without needing to know what DoStuffY does.\n";
if ($y == 0) { print "Yippie! I can go home early!\n\n" };


sub DoStuffX {
  # lost of code involving $x
  $x=$x+1;
  # lots of code involving $x
};

sub DoStuffY {
my $y = shift @_;
  # lost of code involving $y
  $y=$y+1;
  # lots of code involving $y
};

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In reply to Re^2: Global variable vs passing variable from sub to sub by Anonymous Monk
in thread Global variable vs passing variable from sub to sub by kiat

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