2022年10月9日(日) 18:37 Oğuz <oguzismailuy...@gmail.com>: > I'm not familiar with how extended globs are implemented in either shell > but this doesn't look like something that'd involve recursion.
For the particular pattern +(0), you might think it is possible to implement it without recursion, but the extglob engine needs to handle general patterns. Pattern matching that involves the `+' operator is non-deterministic and accepted by the non-deterministic finite automaton (NFA). An efficient implementation for the general patterns would be to emulate the DFA converted from the NFA, which requires some mathematical knowledge. An alternative naive implementation would be to directly handle the NFA by backtracking, where recursion can be used to accumulate the backtracking points. I haven't checked the actual implementations of bash and ksh, but I guess these are implemented in the latter approach. So I think option 4 would be to re-implement the engine by the DFA, though I'm not sure if it is straightforward to take account of the collating symbols [.x.] and equivalence classes [=x=] in the POSIX bracket expressions [...]..
