I have a simple AppleScript that calls a perl shell script to replace a string with another string (here one with two) in files with specified file extensions (here .txt and .xyz). 

It used to work exactly as I have it below, but no longer does (possibly since updating to Mojave last year).

    set CleanFiles to "
    	s/one/two/g;
    	"
    
    set myFolder to choose folder with prompt "Choose a folder with files to be cleaned up:"
    set theFolder to POSIX path of myFolder
    
    do shell script "find " & theFolder & " \\( -name \\*.txt -o -name \\*.xyz \\) -print0 | xargs -0 perl -i -pe '" & CleanFiles & "'"

There is no error message, it seems to run but doesn't do anything. 

What could be wrong?