3 remarks:
1. the two sed commands can be combined into one: ... |sed -e "s/^\/mnt\/us\/documents\///g" -e "s/\//-/g" | grep ...
2. your second-last grep is wrong. Should probably be "\-Gallery", not "\Gallery". \G is not a valid escape code
3. Your last grep is probably useless: you already replaced /mnt/us/documents by "", so there are no occurrences of -mnt-us-documents
"Probably" everywhere because I also didn't test it