Replace

for my $x ( ... ) {
   ...

   if ( ??? ) {
      ...
   }

   ...
}
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my @a = ...;

for my $i ( 0 .. $#a ) {
   my $x = $a[$i];

   ...

   if ( $i == $#a ) {
      ...
   }

   ...
}
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This will work too:

my @a = ...;

for my $x (@a) {
   ...

   if ( \$x == \$a[-1] ) {
      ...
   }

   ...
}
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Warning: As LanX pointed out, the last snippet fails if two elements of the array are aliases of the same scalar.

Update: Added warning.