Question

I’m having trouble understanding what the following code does in a bash completion script:

    case "$last" in
    +\(--import|-i\))
            _filedir '+(txt|html)';;

When is that case ever met? I thought the second line above would be something like

--import|-i)

which does make sense to me. I grepped my bash_completion.d directory for '+\\(' but that one was the only one that came up so I guess it’s not that common.

Answer 1

This code is indeed puzzling without context. As it is, it matches two literal strings –

$ case "+(--import" in +\(--import|-i\)) echo match ;; esac
match
$ case "-i)" in +\(--import|-i\)) echo match ;; esac
match

It looks similar to the extended glob pattern +(--import|-i), but in this form it’s neither a match for the literal pattern (would need to escape the pipe) nor the actual pattern (would need to unescape the parentheses). I’d guess “bug”, but bash completion is a minefield of crazy metaprogramming, so it’s impossible to say without seeing the entire script.

From bash(1)

If the extglob shell option is enabled using the shopt builtin,
several extended pattern matching operators are recognized. In the
following description, a pattern-list is a list of one or more
patterns separated by a |. Composite patterns may be formed using one
or more of the following sub-patterns:

[…]

          +(pattern-list)
                 Matches one or more occurrences of the given patterns