use strict; use warnings;
my ($file_nm,$line_nb,$col_start,$col_end,$string)=@ARGV;
open FILE, "<", $file_nm or die "Cannot open file $file_nm!\n";
open OUT, ">", "~$file_nm" or die "Cannot open temp file ~$file_nm for writing!\n";
while(<FILE>){
    substr( $_, $col_start, $col_end-$col_start+1 ) = $string if $.==$line_nb;
    print OUT $_;
}
close OUT;
close FILE;
rename( "~$file_nm", $file_nm );