#!/usr/bin/perl
use warnings;
use strict;
use 5.010;

foreach my $file (glob "*.txt") {
	my $newfile = $file;
	$newfile =~ s/_oldname_/_newname_/g; 
	if (-e $newfile) {
		warn "can't rename $file to $newfile: $newfile exists\n";
	} elsif (rename $file, $newfile) {
	} else {
	  warn "rename $file to $newfile failed: $!\n";
	}
}
exit;