Hi, try this,

use strict;

my $arg = $ARGV[0];
open(IN,"$arg")||die("Can't open the input file for reading");
undef $/;
my $str = <IN>;
close(IN);

$str=~s#\$[^\$]+\$#&LimitReplace($&)#gei;

open(OUT,">$arg")||die("Can't open the output file for writing");
print OUT $str;
close(OUT);

sub LimitReplace{
 my ($line)=@_;
 $line=~s#\\limits##gi;
 return($line);
}
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