index

my $posa = index($str, $stra);
my $posb = index($str, $strb);

if ($posa < 0 || $posb < 0) {
   print("$stra doesn't occur\n") if $posa < 0;
   print("$strb doesn't occur\n") if $posb < 0;
}
elsif ($posa < $posb) {
   print("$stra first occurs before $strb\n");
}
elsif ($posa > $posb) {
   print("$strb first occurs before $stra\n");
}
else {
   print("$stra and $strb first occur at the same location\n");
}
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Update: Added missing braces.