Lesson 11 · The path separator - Build a Glob and Gitignore Matcher

The path separator

Real patterns match paths, not bare names, and the slash is special - a star must not leap across a directory boundary. Today Match becomes path-aware by splitting on the slash and matching segment by segment, with your finished single-segment matcher doing the work inside each one.

The goal

Match paths segment by segment so the star and question mark never cross a slash.

Start here - the target

TO DO

Scenario: The star stays inside one path segment

Givenpatterns and names that contain slashes

WhenMatch splits both on the slash and matches segment against segment

ThenMatch("*.txt", "a.txt") is true but Match("*.txt", "dir/a.txt") is false, while Match("*/*.txt", "dir/a.txt") is true

Andthe question mark never crosses a slash - Match("a?b", "a/b") is false - and the segment counts must line up: Match("a/b/c", "a/b/c") is true and Match("a/b", "a/b/c") is false

Background

Up to now a pattern matched a single name. Paths introduce a boundary that must be respected: a * should match within one directory level, not swallow slashes and leap across directories. The clean way to get this is to stop treating the whole path as one string. Split the pattern and the name on /, then match segment against segment - the * and ? and classes you built all operate inside a segment, which contains no slashes, so they simply cannot cross one.

Rename your finished matcher to matchSegment and give Match the new job of splitting and looping. Two consequences fall out for free: the segment counts must line up, so a/b does not match a/b/c; and a wildcard is confined to its level, so *.txt matches a.txt but not dir/a.txt, while */*.txt matches dir/a.txt by using one star per segment. All of your earlier single-segment tests still pass, because a pattern with no slash is just a one-segment path. The one thing this cannot yet express is “any number of directories” - that is the double-star, next.

Make it work

// rename the finished single-segment matcher to matchSegment,
// then make Match path-aware
func Match(pattern, name string) bool {
  pat := strings.Split(pattern, "/")
  seg := strings.Split(name, "/")
  if len(pat) != len(seg) { return false }
  for i := range pat {
    if !matchSegment(pat[i], seg[i]) { return false }
  }
  return true
}

CheckpointDONE

Match works path-aware, one segment at a time. Commit and stop here.