The for loop behaves differently depending on how the variable $i is declared. Consider the following two programs -

#!/usr/local/bin/perl -w    #!/usr/local/bin/perl -w
use strict;                 use strict;             

my $i = 45;                 our $i = 45;

for $i (0..67) {            for $i (0..67) {
  last if $i == 10;           last if $i == 10;
  investigate();              investigate();
}                           }
print $i."\n";              print $i."\n";

sub investigate {           sub investigate {
  print "\$i=$i\n";           print "\$i=$i\n";    
}                           }
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The difference is that the left program declares a my variable, while the right program declares an our variable.

However, when I run the programs, I get completely different behaviour inside the for loop:

45                         0
45                         1    
45                         2    
45                         3    
45                         4    
45                         5    
45                         6    
45                         7    
45                         8    
45                         9    
$i=45                      $i=45
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Note that inside the for loop, the value of the top level my $i variable is not affected, while the global our $i variable gets temporarily affected. An interesting observation is made: Perl localizes the $i variable differently inside the for loop, depending on how $i is declared in the first place.

When the top level $i variable is declared as a my variable, the for loop is equivalent to -

my $i = 45;
for (0..67) {
  my $i = $_;
  ...
}
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When the top level $i variable is declared as an our variable, the for loop is equivalent to -

our $i = 45;
for (0..67) {
  local $i = $_;
  ...
[download]