"$ a+b=\sum\limit_a^{n-j}$"

#########
open IN, "abc.xml", or die "$!\n";
open OUT, ">iabc.xml", or die "$!\n";

@txt=<IN>;

foreach $xabc (@txt) {
$find=~ m/\$([^\$]*)\$/g;
$find = "\\limits";
$replace = "";
$find = quotemeta $find;
$xabc =~ s/$find/$replace/g;
print OUT $xabc;
}
close($xabc);