The qx operator forks off a separate process and then runs a shell (usually /bin/sh) to execute the `ls` command.   Perl's glob executes the glob(3) library function directly.

If ls encounters a directory name matching *$caseNumber* then it will descend into that directory and list all the files there.

If any of the file names contains a newline then qx will split it on the newline into separate file names.