(44) 42.

#!/usr/bin/perl
use strict;
sub filegrep {
#         1         2         3         4         5
#12345678901234567890123456789012345678901234567890123456
 my$a=$_[0];grep{open F,$_;grep/$a/,<F>}(<*>)
}
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Antonio

Update: gets down to 42 omitting the parenthesis in (<*>). It becomes

#12345678901234567890123456789012345678901234567890123456
 my$a=$_[0];grep{open F,$_;grep/$a/,<F>}<*>
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Update²: As pointed out by others, the usage of variable $a is totally useless.
Update³: If $a were of any use, one wouldn't need my anyway, since $a and $b are special (think sort) and don't upset strict.
Update⁴: As observed by crazyinsomniac, $a becomes global refers to the package global $a without my.which is a bad thing. This is a potentially bad thing.

The stupider the astronaut, the easier it is to win the trip to Vega - A. Tucket