How to replace a string in an existing file in Perl?

Question

I want to replace word \"blue\" to \"red\" in all text files named as 1_classification.dat, 2_classification.dat and so on. I want to edit the same file so I tried this code

Answer 1

None of the existing answers here has provided a complete example of how to do this from within a script (not a one-liner). Here is what I did:

rename($file, $file.'.bak');
open(IN, '<'.$file.'.bak') or die $!;
open(OUT, '>'.$file) or die $!;
while()
{
    $_ =~ s/blue/red/g;
    print OUT $_;
}
close(IN);
close(OUT);