use strict;
use warnings;

my $foo;
my $bar = 1;

if( $bar - 1 ) {             # line 7
  print $bar;
} elsif( $foo - 1 ) {        # throws warning -- at line 7!
  print "$foo\n";
  my $baz = 2 * $foo;
}

__END__
Use of uninitialized value in subtraction (-) at - line 7.
Use of uninitialized value in concatenation (.) or string at - line 10.

Use of uninitialized value in multiplication (*) at - line 11.