# First three lines of your subroutine, ir() with the prototype removed because it's not useful:

sub ir {
    my $prefix = shift @_;
    $prefix=~ s/_$//;
    print $prefix,"\n";
}

# A loop to test those first three lines of your code to see if they work:

while(<DATA>) {
    chomp;
    ir($_);
}

# Sample input you provided:

__DATA__
DCMS_DEMO_
DCMS_DEMO_new_block2_
DCMS_DEMO_new_block2_checklist_tmp_
DCMS_DEMO_new_block2_checklist_tmp_rev1_

##</code><code>##

DCMS_DEMO
DCMS_DEMO_new_block2
DCMS_DEMO_new_block2_checklist_tmp
DCMS_DEMO_new_block2_checklist_tmp_rev1