}

	verout, err := testenv.Command(t, gpath, "--version").CombinedOutput()
	if err != nil {
		t.Logf("%s", verout)
		t.Fatal(err)
	}
	vers := regexp.MustCompile(`(\d+)\.(\d+)`).FindSubmatch(verout)
	if len(vers) == 0 {
		t.Fatalf("could not find version number in %s", verout)
	}
	major, err := strconv.Atoi(string(vers[1]))
	if err != nil {
		t.Fatal(err)
	}

	fmt.Printf("%q\n", re.FindAllSubmatch([]byte(`seafood fool`), -1))

	// Output:
	// [["food" "d"] ["fool" "l"]]
}

func ExampleRegexp_FindSubmatch() {
	re := regexp.MustCompile(`foo(.?)`)
	fmt.Printf("%q\n", re.FindSubmatch([]byte(`seafood fool`)))

	// Output:
	// ["food" "d"]
}

func ExampleRegexp_Match() {
	re := regexp.MustCompile(`foo.?`)
	fmt.Println(re.Match([]byte(`seafood fool`)))

	status, err := os.ReadFile(fmt.Sprintf("/proc/%d/status", pid))
	if err != nil {
		t.Logf("couldn't get proc tracer: %s", err)
		return
	}
	re := regexp.MustCompile(`TracerPid:\s+([0-9]+)`)
	sub := re.FindSubmatch(status)
	if sub == nil {
		t.Logf("couldn't find proc tracer PID")
		return
	}
	if string(sub[1]) == "0" {
		return
	}
	t.Skip("test will deadlock under a debugger")
}

	if a == nil {
		return nil
	}
	return a[0:2]
}

// FindSubmatch returns a slice of slices holding the text of the leftmost
// match of the regular expression in b and the matches, if any, of its
// subexpressions, as defined by the 'Submatch' descriptions in the package
// comment.
// A return value of nil indicates no match.
func (re *Regexp) FindSubmatch(b []byte) [][]byte {
	var dstCap [4]int

			t.Errorf("match %d: expected %q got %q: %s", n, expect, got, test)
			return
		}
	}
}

func TestFindSubmatch(t *testing.T) {
	for _, test := range findTests {
		result := MustCompile(test.pat).FindSubmatch([]byte(test.text))
		switch {
		case test.matches == nil && result == nil:
			// ok
		case test.matches == nil && result != nil:
			t.Errorf("expected no match; got one: %s", test)

}

func (f *exitCodeFilter) Finish() (int, error) {
	// f.buf could be empty, contain a partial match of exitRe, or
	// contain a full match.
	b := f.buf.Bytes()
	defer f.buf.Reset()
	match := f.exitRe.FindSubmatch(b)
	if len(match) < 2 || match[1] == nil {
		// Not a full match. Flush.
		if _, err := f.w.Write(b); err != nil {
			return 0, err
		}
		return 0, fmt.Errorf("no exit code (in %q)", string(b))
	}

	out, err := exec.Command("gdb", "--version").CombinedOutput()
	if err != nil {
		t.Skipf("skipping: error executing gdb: %v", err)
	}
	re := regexp.MustCompile(`([0-9]+)\.([0-9]+)`)
	matches := re.FindSubmatch(out)
	if len(matches) < 3 {
		t.Skipf("skipping: can't determine gdb version from\n%s\n", out)
	}
	major, err1 := strconv.Atoi(string(matches[1]))
	minor, err2 := strconv.Atoi(string(matches[2]))

)

func findImportComment(file string) string {
	data, err := os.ReadFile(file)
	if err != nil {
		return ""
	}
	m := importCommentRE.FindSubmatch(data)
	if m == nil {
		return ""
	}
	path, err := strconv.Unquote(string(m[1]))
	if err != nil {
		return ""
	}
	return path
}

// WriteOpts control the behavior of WriteGoMod.

	// The string looks like
	//	test coverage for encoding/binary: 79.9% of statements
	// Extract the piece from the percentage to the end of the line.
	re := regexp.MustCompile(`coverage: (.*)\n`)
	matches := re.FindSubmatch(out)
	if matches == nil {
		// Probably running "go test -cover" not "go test -cover fmt".
		// The coverage output will appear in the output directly.
		return ""
	}

	sh := b.BackgroundShell()
	out, err := sh.runOut(".", nil, "swig", "-version")
	if err != nil {
		return err
	}
	re := regexp.MustCompile(`[vV]ersion +(\d+)([.]\d+)?([.]\d+)?`)
	matches := re.FindSubmatch(out)
	if matches == nil {
		// Can't find version number; hope for the best.
		return nil
	}

	major, err := strconv.Atoi(string(matches[1]))
	if err != nil {