local $/;

my $search  = <>;
my $replace = <>;

#local $^I = '';  # No backups.
local $^I = '~';  # Make backups.
while (<>) {
   s/\Q$search/$replace/g;
   print;
}

##</code><code>##

$ script.pl - - *.cstol
search
search
search
^D
replace
replace
replace
^D

##</code><code>##

$ script.pl search.txt replace.txt *.cstol