my @match = do {
    open my $fh, '<', $file or die "$!";
    grep /^$ARGV[0]\|/, <$fh>;
};

##</code><code>##

my @match;
{
    open my $fh, '<', $file or die "$!";
    local $_;
    my $rx = qr/^$ARGV[0]\|/
    m/$rx/ && push @match, $_ while <$fh>;
}

##</code><code>##

sub grep_file {
    my ($rx, $file) = @_;
    my @match;
    local $_;
    open my $fh, '<', $file or die "$!";
    my $rx = qr/^$rx\|/
    m/$rx/ && push @match, $_ while <$fh>;
    @match;
};

my @match = grep_file($ARGV[0], $file);