How about a simple grep: 
my $str_a = 'Foo';                                # Can be any length
for my $str_b (grep /^$str_a/, @list ) {                         # Can
+ be any number of items
    expensive_function($str_a , $str_b);
}

[download]
Will call expensive_function only on items that start with 'Foo' (Which can be limited to one character if thats what you Really want)

Update: This is the same as delirium's solution, above.

Offense, like beauty, is in the eye of the beholder, and a fantasy.
By guaranteeing freedom of expression, the First Amendment also guarntees offense.

In reply to Re: Matching First Character of Strings Efficiently by NetWallah
in thread Matching First Character of Strings Efficiently by Limbic~Region

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