BF: combineScript uses bash-isms

https://www.jiscmail.ac.uk/cgi-bin/wa-jisc.exe?A2=FSL;887f0bfc.2204 reports "Bad substitution" errors running the randomise_parallel defragment script. This is probably due to the script's shebang being

#!/bin/sh

but the code uses bashisms, so it will fail on systems where sh does not default to bash.