Function _translate_alternatives

src/borg/helpers/shellpattern.py:108–140

Translates the shell-style alternative portions of the pattern to regular expression groups. For example: {alt1,alt2} -> (alt1|alt2)

(pat)

def _translate_alternatives(pat):
    """Translates the shell-style alternative portions of the pattern to regular expression groups.

    For example: {alt1,alt2} -> (alt1|alt2)
    """
    # Parse pattern for paired braces.
    brace_pairs = _parse_braces(pat)

    pat_list = list(pat)  # Convert to list in order to subscript characters.

    # Convert non-escaped commas within groups to pipes.
    # Passing, e.g. "{a\,b}.txt" to the shell expands to "{a,b}.txt", whereas
    # "{a\,,b}.txt" expands to "a,.txt" and "b.txt"
    for opening, closing in brace_pairs:
        commas = 0

        for i in range(opening + 1, closing):  # Convert non-escaped commas to pipes.
            if pat_list[i] == ",":
                if i == opening or pat_list[i - 1] != "\\":
                    pat_list[i] = "|"
                    commas += 1
            elif pat_list[i] == "|" and (i == opening or pat_list[i - 1] != "\\"):
                # Nested groups have their commas converted to pipes when traversing the parent group.
                # So in order to confirm the presence of a comma in the original, shell-style pattern,
                # we must also check for a pipe.
                commas += 1

        # Convert paired braces into parentheses, but only if at least one comma is present.
        if commas > 0:
            pat_list[opening] = "("
            pat_list[closing] = ")"

    return "".join(pat_list)