Seems like a job for grep e.g

if( grep { $a == $a[$_] && $b eq $b[$_] } 0 .. $#a ) {
  # do stuff here
}
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See. the grep docs for more info.

Update: and here's the cleaner approach using List::Util's first (as kindly pointed out by Zed_Lopez below)

if( first { $a == $a[$_] && $b eq $b[$_] } 0 .. $#a ) {
  # do stuff here
}
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