If you insist on just wrapping grep in a subroutine...

my $array = [ 1 .. 50 ];

sub mygrep {
  my( $guess, $array ) = @_;
  grep { $_ == $guess } @{$array};
}

print mygrep( 165, $array ) ? "True\n" : "False\n";
[download]

Enjoy!

--
Casey
   I am a superhero.