use diagnostics;
use strict;
open (FILE, "c:\\my\\dir\\src.file.txt")
	 || die "failed to open src file";
while (<FILE>){
	my $var_a = $_;
	my $var_b = "_INDEX";
	my $var_c = $_;
	$var_a =~ s/(^[A-Z]{4})(.*)/$1/o;
	$comb = $var_a . $var_b;
	open ($comb, "c:\\my\\dest\\dir\\" . $comb . "found.txt")
		 || die "failure to create" . $comb;
	print $comb $var_c . "content detail for file found\n";
	}
close FILE;

#_## do some other functions that add more information to file.

close $comb.

##</code><code>##

WORKS:	open ('$comb', "c:\\my\\dest\\dir\\" . $comb . "found.txt")

Unable to figure out the print function.

ERROR:	print $comb $var_c . "content detail for file found\n";