Globbing, Quoting, and Expansion

Modeling glob expansion and the quoting rules as pure string/array logic -- no shell is invoked by this or any exercise in this course.

function expandGlob(pattern, filesInDirectory) {
  // A simplified model: '*' matches any sequence of characters. Splitting the
  // pattern on '*' and checking each filename starts/ends with the right
  // pieces avoids needing a full glob-to-regex translator for this example.
  const parts = pattern.split("*");
  function matches(filename) {
    if (parts.length === 1) return filename === pattern;
    if (!filename.startsWith(parts[0])) return false;
    if (!filename.endsWith(parts[parts.length - 1])) return false;
    return true;
  }
  const results = filesInDirectory.filter(matches);
  return results.length > 0 ? results : [pattern]; // Bash's real default: unmatched glob stays LITERAL
}

console.log(expandGlob("*.txt", ["draft.txt", "final.txt", "image.png"]));
// ["draft.txt", "final.txt"] -- the command never sees the literal "*.txt"

console.log(expandGlob("*.pdf", ["draft.txt", "final.txt"]));
// ["*.pdf"] -- NO match: Bash's default passes the literal pattern through, not an empty list

function wordSplit(value) {
  // Models what happens to an UNQUOTED variable expansion: split on whitespace.
  return value.split(/\s+/).filter(Boolean);
}
console.log(wordSplit("my file.txt")); // ["my", "file.txt"] -- TWO arguments, not one -- the real bug unquoted vars cause

Call wordSplit with a value that has no spaces at all, and confirm it correctly produces just ONE argument.

This models glob expansion only -- no shell or filesystem is touched. Write expandGlob(pattern, filesInDirectory) for patterns containing exactly one '*': match any filename starting with the text before '*' and ending with the text after it. If nothing matches, return [pattern] (Bash's real default: an unmatched glob is left literal, not empty).

Checks: expands a glob pattern to every matching filename · leaves an unmatched glob pattern literal, matching Bash's real default behavior

This models word-splitting only -- no shell is invoked. Write commandArgsFromUnquoted(value) modeling what an UNQUOTED variable expansion produces: split on any whitespace, filtering out empty pieces (multiple spaces shouldn't create empty arguments). Then write commandArgsFromDoubleQuoted(value) modeling a DOUBLE-QUOTED expansion: always return a single-element array [value], regardless of any spaces inside.

Checks: unquoted expansion word-splits into multiple arguments · double-quoted expansion stays as one argument regardless of spaces · a value with no spaces produces one argument either way