Rather than using an intermediate array and saving its first element, you could save the first element from the list that grep produces.

($curFrom) = grep(/^From:/, @header);
($curSubject) = grep(/^Subject:/, @header);
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Note that using the 'o' modifier on the regular expression does not offer a benefit in this instance. It is only useful when the regular expression would be re-evaluated on each execution (as when it includes a variable).