perl -p -i.bak -e 's:CLASSATTRIBUTES:classattributes:g' *

##</code><code>##

my @files = qw( foobar zoot );

for my $file ( @files ) {
    ## Read the contents of the file
    open FILE, "<$file";
    my $contents; do { local $/; $contents = <FILE>; };
    close FILE;

    ## Make your changes
    $contents =~ s:CLASSATTRIBUTES:classattributes:g;

    ## Write the modified contents back to the file
    open FILE, ">$file";
    print FILE $contents;
    close FILE;
}