$(var:pos[:len]) # extract substr from pos (0-based) for len
$(var/substr/repl) # replace first match
$(var//substr/repl) # replace all matches
$(var/#substr/repl) # replace if matches at beginning (non-greedy)
$(var/##substr/repl) # replace if matches at beginning (greedy)
$(var/%substr/repl) # replace if matches at end (non-greedy)
$(var/%%substr/repl) # replace if matches at end (greedy)
${#var} # returns length of $var
${!var} # indirect expansion
