sub my_grep {
 my ($filename, $re) = @_;
 open my $fh, '<', $filename or die "cannot open $filename - $!";
 my @matching_lines = grep /$re/, <$fh>;
 close $fh or die "cannot close $filename - $!";
 return @matching_lines; # might need further chomping?
}

my $group_re = qr{^samplegrp:};
foreach my $grpfile (glob "group/server*.grp") {
  print "$grpfile: ", my_grep($grpfile, $group_re), "\n";
}