It is like you read my script.sh over my shoulder as I was writing it. :)

Out it interest why not xarg or find’s exec

It clearly depends on what good that subshell running ls does for you, but the trivial form would be:

  for i in *txt
  do
    ...
  done

The reason to stuff every file name through ls (keep in mind that it's always your shell doing glob expansions, ls is not involved) would be to sort them by creation date or some other processing that ls can do. But as soon as there are many files involved, or those sorting arguments gets non-trivial, it will fall apart completely.

Use find | while read instead, or xargs. That's going to be easier on the eyes and actually work.

  for i in *; do
    ...;
  done

works even better as it can handle files with whitespace. I usually disable file globbing but enable it specifically for code like this.

EDIT: Actually, one issue with the above is that if there aren't any matching files then you get a literal "*". But I'd rather deal with that then break when filenames have embedded whitespace.