Unix glob() function and formal language equivalence
Every glob expression can be recognized with a regular expression (the translation is straightforward).  Every regular language is also context-free, and there is a straightforward translation: convert the regular expression to a DFA, then turn that into a pushdown automaton that never uses or looks at its stack.  So, it follows that every glob expression can be recognized by some pushdown automaton, i.e., it recognizes a context-free language.