dwim: take the scan flags (closes #162)

dwim now takes --workers, -x, --no-default-excludes and --exclude with the meaning they have for scan. One scanOptions struct, one function that adds the flags and one PreRunE check serve both commands, and runScan takes the struct instead of four separate values. The dwim help says that the scan runs with the same flags, and lists the default excludes, as the scan help does. Model: opus-5-5
2026-11-11 06:56:08 +00:00
1 parent db56fd0e4c
commit dc82531aec
@@ -254,15 +254,14 @@ In order:
 - `report` prints the file-level duplicate report from the database.
 - `trees` prints the duplicate-tree report from the database.
 - `info` prints the database's details.
- `dwim` scans `/` with the default excludes, then prints the duplicate-tree
-  report.
+- `dwim` scans `/`, then prints the duplicate-tree report.

 ```
 sfdupes scan [--workers N] [-x] [--no-default-excludes] [--exclude PATH]... PATH...
 sfdupes report > dupes.tsv
 sfdupes trees > dupetrees.tsv
 sfdupes info
-sfdupes dwim
+sfdupes dwim [--workers N] [-x] [--no-default-excludes] [--exclude PATH]...
 sfdupes --version
 sfdupes [command] --help
 ```
@@ -292,20 +291,20 @@ The reference below is also the program's specification.
  database is `/var/lib/sfdupes/db.sqlite`. There is no command-line flag for
  it. The path names the file exactly, whatever characters it holds. A relative
  path is relative to the working directory.
- `--workers N` (`scan`) sets how many directories `scan` reads at once while it
-  lists the trees. It also sets how many files `scan` reads at once while it
-  hashes them. The default is the number of CPUs. `N` must be at least 1. A
-  smaller value is a usage error, reported in one line on stderr with exit 2
-  before anything is scanned.
- `-x`, `--one-file-system` (`scan`) keeps the walk of each operand out of
-  directories on other filesystems, as the same flag does for `du` and `rsync`.
-  By default the walk also enters directories on other filesystems.
- `--no-default-excludes` (`scan`) lets the walk enter the default excludes.
-  Those are the system and temporary directories the walk otherwise leaves out,
-  such as `/var/tmp` on Linux (see "Rules for the walk").
- `--exclude PATH` (`scan`) keeps the walk out of `PATH` and everything below
-  it. `PATH` may be a directory or a file. The flag may be given more than once.
-  The walk knows `PATH` by its device ID and inode number, as it knows the
+- `--workers N` (`scan`, `dwim`) sets how many directories `scan` reads at once
+  while it lists the trees. It also sets how many files `scan` reads at once
+  while it hashes them. The default is the number of CPUs. `N` must be at
+  least 1. A smaller value is a usage error, reported in one line on stderr with
+  exit 2 before anything is scanned.
+- `-x`, `--one-file-system` (`scan`, `dwim`) keeps the walk of each operand out
+  of directories on other filesystems, as the same flag does for `du` and
+  `rsync`. By default the walk also enters directories on other filesystems.
+- `--no-default-excludes` (`scan`, `dwim`) lets the walk enter the default
+  excludes. Those are the system and temporary directories the walk otherwise
+  leaves out, such as `/var/tmp` on Linux (see "Rules for the walk").
+- `--exclude PATH` (`scan`, `dwim`) keeps the walk out of `PATH` and everything
+  below it. `PATH` may be a directory or a file. The flag may be given more than
+  once. The walk knows `PATH` by its device ID and inode number, as it knows the
  database files (see "Rules for the walk"). So the walk leaves `PATH` out
  whatever path leads to it. That includes a hard link to a file given as
  `PATH`. A symlink given as `PATH` excludes its target. An empty `PATH`, as in
@@ -318,9 +317,9 @@ The reference below is also the program's specification.
 - `--help`, `-h`, alone or after a subcommand, prints the help text to stderr
  and exits 0. It writes nothing to stdout. The help of `sfdupes` and of `scan`
  names the database. The help of `report`, `trees`, `info` and `dwim` says what
-  each prints. `sfdupes scan --help` also lists the default excludes of the
-  system it runs on, and the filesystem types the walk never records anything
-  on.
+  each prints. `sfdupes scan --help` and `sfdupes dwim --help` also list the
+  default excludes of the system they run on, and the filesystem types the walk
+  never records anything on.

 ### Duplicate detection

@@ -858,14 +857,25 @@ trees: 14 records read, 1 duplicate tree groups, 1 dupe trees, 3.0 KiB reclaimab
 ### `dwim` mode

 `dwim`, short for "do what I mean", scans a new machine and reports its
-duplicate trees in one command. It takes no positional arguments and no flags of
-its own. Like `scan`, it should run as root, so that it can read every file.
+duplicate trees in one command. It takes no positional arguments. Like `scan`,
+it should run as root, so that it can read every file.

-`dwim` runs what `sfdupes scan /` runs with no flags. The walk skips the default
-excludes and crosses into other filesystems. `--workers` keeps its default. The
+`dwim` takes these flags of `scan`, with the same meaning (see "Settings"):
+
+- `--workers N`;
+- `-x`, `--one-file-system`;
+- `--no-default-excludes`;
+- `--exclude PATH`, which may be given more than once.
+
+`dwim` runs what `sfdupes scan /` runs with the same flags. With no flags, the
+walk skips the default excludes and crosses into other filesystems. The
 database, its creation and the scan lock are those of `scan`. Then `dwim` runs
 what `sfdupes trees` runs. The largest trees come first.

+```
+sfdupes dwim -x --exclude /srv/cache
+```
+
 The report goes to stdout, exactly as `trees` prints it. On stderr comes what
 `scan` prints, then what `trees` prints, then one last line:

@@ -29,6 +29,10 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.

+- `dwim` takes the `scan` flags `--workers`, `-x`, `--no-default-excludes` and
+  `--exclude`, with the same meaning. Both commands register and check them with
+  the same code (2026-11-11, https://git.eeqj.de/sneak/sfdupes/issues/162)
+
 - The help of `sfdupes` and of `scan` names the database, its default path and
  `SFDUPES_DATABASE`. The help of `report` and `trees` lists the columns, the
  order of the rows and the escapes. The help of `info` lists its lines. The
@@ -358,8 +358,9 @@ func TestRunScanInterrupted(t *testing.T) {
 	stderr := captureStderr(t)
 	dir := buildSmokeTree(t)

-	err := runScan(t.Context(), []string{dir}, walkCancelWorkers, false,
-		false, nil)
+	opts := scanOptions{workers: walkCancelWorkers}
+
+	err := runScan(t.Context(), []string{dir}, opts)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -382,8 +383,7 @@ func TestRunScanInterrupted(t *testing.T) {
 	go func() {
 		defer close(done)

-		err = runScan(cancelledContext(t), []string{dir}, walkCancelWorkers,
-			false, false, nil)
+		err = runScan(cancelledContext(t), []string{dir}, opts)
 	}()

 	awaitReturn(t, done, "runScan")
@@ -410,8 +410,7 @@ func TestRunScanInterrupted(t *testing.T) {
 			got, before)
 	}

-	err = runScan(t.Context(), []string{dir}, walkCancelWorkers, false,
-		false, nil)
+	err = runScan(t.Context(), []string{dir}, opts)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -437,7 +436,7 @@ func TestRunScanInterruptedMidHash(t *testing.T) {
 	dir := buildWalkCancelTree(t)

 	err := runScan(newWalkClock(hashCancelAtDone), []string{dir},
-		walkCancelWorkers, false, false, nil)
+		scanOptions{workers: walkCancelWorkers})
 	if !errors.Is(err, errInterrupted) {
 		t.Fatalf("runScan interrupted mid-hash = %v, want %v",
 			err, errInterrupted)
@@ -88,10 +88,10 @@ value, separated by a tab:
  size of recorded files  their total size, in bytes, then rounded
 `

-	dwimHelp = `dwim runs what "sfdupes scan /" runs, then what "sfdupes trees" runs.
-Run it as root, so that the scan can read every file. The scan is stored
-in the database, as scan stores it, so "sfdupes trees" prints the report
-again later.
+	dwimHelp = `dwim runs what "sfdupes scan /" runs with the same flags, then what
+"sfdupes trees" runs. Run it as root, so that the scan can read every
+file. The scan is stored in the database, as scan stores it, so
+"sfdupes trees" prints the report again later.
 `
 )

@@ -100,12 +100,11 @@ again later.
 // cobra prints for it is the whole message.
 var errNoSubcommand = errors.New("no subcommand")

-// errWorkersBelowOne is the usage error for a scan --workers value
-// below 1.
+// errWorkersBelowOne is the usage error for a --workers value below 1.
 var errWorkersBelowOne = errors.New("--workers must be at least 1")

-// errEmptyExcludeValue is the usage error for an empty scan --exclude
-// value, as from --exclude "$DIR" with DIR unset. Taken as a path, it
+// errEmptyExcludeValue is the usage error for an empty --exclude value,
+// as from --exclude "$DIR" with DIR unset. Taken as a path, it
 // would name the working directory.
 var errEmptyExcludeValue = errors.New("--exclude must not be empty")

@@ -256,83 +255,116 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		}),
 	}

-	dwimCmd := &cobra.Command{
-		Use:   cmdDwim,
-		Short: "Scan / with the default excludes, then print the duplicate-tree report",
-		Args:  cobra.NoArgs,
-		RunE: runE(func(ctx context.Context, _ []string) error {
-			return runDwim(ctx, "/", stdout)
-		}),
-	}
-
 	root.Long = root.Short + ".\n\n" + databaseHelp
 	reportCmd.Long = reportCmd.Short + ".\n\n" + reportHelp
 	treesCmd.Long = treesCmd.Short + ".\n\n" + treesHelp
 	infoCmd.Long = infoCmd.Short + ".\n\n" + infoHelp
-	dwimCmd.Long = dwimCmd.Short + ".\n\n" + dwimHelp

-	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd, dwimCmd)
+	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd,
+		newDwimCommand(stdout))

 	return root
 }

-// newScanCommand builds the scan subcommand, with its --workers, -x,
-// --no-default-excludes and --exclude flags. Its help names the
+// scanOptions holds the values of the flags that scan and dwim share:
+// --workers, -x, --no-default-excludes and --exclude.
+type scanOptions struct {
+	workers           int
+	oneFS             bool
+	noDefaultExcludes bool
+	excludePaths      []string
+}
+
+// scanFlagsUsage names the flags that scan and dwim share, for their
+// usage lines.
+const scanFlagsUsage = "[--workers N] [-x] [--no-default-excludes] " +
+	"[--exclude PATH]..."
+
+// addScanFlags adds the flags that scan and dwim share to cmd, which
+// stores their values in opts.
+func addScanFlags(cmd *cobra.Command, opts *scanOptions) {
+	cmd.Flags().IntVar(&opts.workers, "workers", runtime.NumCPU(),
+		"concurrent workers for the walk and hash phases")
+	cmd.Flags().BoolVarP(&opts.oneFS, "one-file-system", "x", false,
+		"do not cross filesystem boundaries")
+	cmd.Flags().BoolVar(&opts.noDefaultExcludes, "no-default-excludes",
+		false, "enter the default excludes, the paths listed above")
+	// A string array, not a slice, so a comma in a path is not a
+	// separator.
+	cmd.Flags().StringArrayVar(&opts.excludePaths, "exclude", nil,
+		"never enter or record `PATH` or anything below it; repeatable")
+}
+
+// check rejects the flag values that are usage errors, before the
+// command runs. It is the PreRunE of scan and dwim.
+func (o *scanOptions) check(cmd *cobra.Command, _ []string) error {
+	err := checkScanWorkers(cmd, o.workers)
+	if err != nil {
+		return err
+	}
+
+	return rejectEmptyExcludeValue(cmd, o.excludePaths)
+}
+
+// newScanCommand builds the scan subcommand. Its help names the
 // database, and lists the default excludes of the system it runs on and
 // the filesystem types it never records anything on.
 func newScanCommand() *cobra.Command {
-	var (
-		scanWorkers           int
-		scanOneFS             bool
-		scanNoDefaultExcludes bool
-		scanExclude           []string
-	)
+	var opts scanOptions

 	short := "Walk trees and synchronize the scan database"

 	scanCmd := &cobra.Command{
-		Use: cmdScan + " [--workers N] [-x] [--no-default-excludes] " +
-			"[--exclude PATH]... PATH...",
+		Use: cmdScan + " " + scanFlagsUsage + " PATH...",
 		// The Use line already names every flag, so cobra must not
 		// append its generic "[flags]" to it.
 		DisableFlagsInUseLine: true,
 		Short:                 short,
 		Long: short + ".\n\n" + databaseHelp + "\n" +
 			defaultExcludesHelp(runtime.GOOS),
-		Args: cobra.MinimumNArgs(1),
-		PreRunE: func(cmd *cobra.Command, _ []string) error {
-			err := checkScanWorkers(cmd, scanWorkers)
-			if err != nil {
-				return err
-			}
-
-			return rejectEmptyExcludeValue(cmd, scanExclude)
-		},
+		Args:    cobra.MinimumNArgs(1),
+		PreRunE: opts.check,
 		RunE: runE(func(ctx context.Context, args []string) error {
 			ctx, stop := interruptContext(ctx)
 			defer stop()

-			return runScan(ctx, args, scanWorkers, scanOneFS,
-				scanNoDefaultExcludes, scanExclude)
+			return runScan(ctx, args, opts)
 		}),
 	}
-	scanCmd.Flags().IntVar(&scanWorkers, "workers", runtime.NumCPU(),
-		"concurrent workers for the walk and hash phases")
-	scanCmd.Flags().BoolVarP(&scanOneFS, "one-file-system", "x", false,
-		"do not cross filesystem boundaries")
-	scanCmd.Flags().BoolVar(&scanNoDefaultExcludes, "no-default-excludes",
-		false, "enter the default excludes, the paths listed above")
-	// A string array, not a slice, so a comma in a path is not a
-	// separator.
-	scanCmd.Flags().StringArrayVar(&scanExclude, "exclude", nil,
-		"never enter or record `PATH` or anything below it; repeatable")
+	addScanFlags(scanCmd, &opts)

 	return scanCmd
 }

-// checkScanWorkers rejects a scan --workers value below 1. That is a
-// usage error reported in one line: cobra prints the returned message
-// without the usage text, and run exits 2.
+// newDwimCommand builds the dwim subcommand, which takes the scan flags
+// with the meaning they have for scan. Its help says what dwim runs,
+// then lists the default excludes and the filesystem types the scan
+// never records anything on.
+func newDwimCommand(stdout io.Writer) *cobra.Command {
+	var opts scanOptions
+
+	short := "Scan /, then print the duplicate-tree report"
+
+	dwimCmd := &cobra.Command{
+		Use:                   cmdDwim + " " + scanFlagsUsage,
+		DisableFlagsInUseLine: true,
+		Short:                 short,
+		Long: short + ".\n\n" + dwimHelp + "\n" +
+			defaultExcludesHelp(runtime.GOOS),
+		Args:    cobra.NoArgs,
+		PreRunE: opts.check,
+		RunE: runE(func(ctx context.Context, _ []string) error {
+			return runDwim(ctx, "/", opts, stdout)
+		}),
+	}
+	addScanFlags(dwimCmd, &opts)
+
+	return dwimCmd
+}
+
+// checkScanWorkers rejects a --workers value below 1. That is a usage
+// error reported in one line: cobra prints the returned message without
+// the usage text, and run exits 2.
 func checkScanWorkers(cmd *cobra.Command, workers int) error {
 	if workers >= 1 {
 		return nil
@@ -343,7 +375,7 @@ func checkScanWorkers(cmd *cobra.Command, workers int) error {
 	return fmt.Errorf("%w, got %d", errWorkersBelowOne, workers)
 }

-// rejectEmptyExcludeValue rejects an empty scan --exclude value. That
+// rejectEmptyExcludeValue rejects an empty --exclude value. That
 // is a usage error reported in one line, as for --workers below 1.
 func rejectEmptyExcludeValue(cmd *cobra.Command, excludePaths []string) error {
 	if !slices.Contains(excludePaths, "") {
@@ -25,6 +25,9 @@ const usageMarker = "Usage:"
 // helpFlag asks for the help text.
 const helpFlag = "--help"

+// workersFlag is the scan and dwim flag that sets the worker count.
+const workersFlag = "--workers"
+
 // TestMain stops the tests at once, saying why, when their temporary
 // directory is not on a persistent filesystem: scan records nothing
 // there (README "Rules for the walk"), so most scan tests would fail
@@ -573,8 +576,8 @@ func TestRunNamesDefaultDatabase(t *testing.T) {
 	}{
 		cmdScan: {
 			run: func() error {
-				return runScan(t.Context(), []string{missing}, 1, false, false,
-					nil)
+				return runScan(t.Context(), []string{missing},
+					scanOptions{workers: 1})
 			},
 			want: scanWant,
 		},
@@ -665,7 +668,7 @@ func TestRunScanRejectsWorkersBelowOne(t *testing.T) {

 			var stdout, stderr bytes.Buffer

-			args := []string{cmdScan, "--workers", workers, t.TempDir()}
+			args := []string{cmdScan, workersFlag, workers, t.TempDir()}

 			code := run(args, &stdout, &stderr)
 			if code != exitUsage {
@@ -5,20 +5,20 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"runtime"
 )

 // runDwim implements the dwim subcommand: it runs what "sfdupes scan
-// root" runs with no flags, then what "sfdupes trees" runs, and ends
-// with a line on stderr saying how to print the report again. The dwim
-// command passes "/" as root. It catches SIGINT and SIGTERM as scan
-// does, but only during the scan. An error from the scan, an interrupt
-// included, ends it before the report. During the report, a signal
-// ends it at once, as it ends trees.
-func runDwim(ctx context.Context, root string, stdout io.Writer) error {
+// root" runs with the scan flags in opts, then what "sfdupes trees"
+// runs, and ends with a line on stderr saying how to print the report
+// again. The dwim command passes "/" as root. It catches SIGINT and
+// SIGTERM as scan does, but only during the scan. An error from the
+// scan, an interrupt included, ends it before the report. During the
+// report, a signal ends it at once, as it ends trees.
+func runDwim(
+	ctx context.Context, root string, opts scanOptions, stdout io.Writer,
+) error {
 	scanCtx, stop := interruptContext(ctx)
-	err := runScan(scanCtx, []string{root}, runtime.NumCPU(), false, false,
-		nil)
+	err := runScan(scanCtx, []string{root}, opts)

 	stop()

@@ -2,7 +2,10 @@ package sfdupes //nolint:testpackage // calls the unexported runDwim

 import (
 	"bytes"
+	"errors"
+	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 )
@@ -28,7 +31,7 @@ func TestRunDwimPrintsLargestTreesFirst(t *testing.T) {

 	stderr := captureStderr(t)

-	err := runDwim(t.Context(), root, &stdout)
+	err := runDwim(t.Context(), root, scanOptions{workers: 1}, &stdout)
 	if err != nil {
 		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
 	}
@@ -67,7 +70,7 @@ func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {

 	stderr := captureStderr(t)

-	err := runDwim(t.Context(), missing, &stdout)
+	err := runDwim(t.Context(), missing, scanOptions{workers: 1}, &stdout)
 	if err == nil {
 		t.Fatal("runDwim on a missing root: error = nil, want it fatal")
 	}
@@ -81,3 +84,127 @@ func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
 		t.Errorf("stderr = %q, want nothing from trees or dwim", got)
 	}
 }
+
+func TestRunDwimExcludeLeavesTreeOut(t *testing.T) {
+	// dwim passes its --exclude paths to the scan: an excluded copy is
+	// not recorded, so its pair is not reported.
+	t.Setenv(databaseEnv, testDBPath(t))
+
+	root := realTempDir(t)
+
+	kept := []string{
+		filepath.Dir(writeFile(t, root, "a1/f.bin", pattern(1, 300))),
+		filepath.Dir(writeFile(t, root, "a2/f.bin", pattern(1, 300))),
+	}
+	writeFile(t, root, "b1/f.bin", pattern(2, 5000))
+	excluded := filepath.Dir(writeFile(t, root, "b2/f.bin", pattern(2, 5000)))
+
+	var stdout bytes.Buffer
+
+	stderr := captureStderr(t)
+
+	opts := scanOptions{workers: 1, excludePaths: []string{excluded}}
+
+	err := runDwim(t.Context(), root, opts, &stdout)
+	if err != nil {
+		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
+	}
+
+	lines := strings.Split(strings.TrimSuffix(stdout.String(), "\n"), "\n")
+	if len(lines) != 2 {
+		t.Fatalf("stdout = %q, want a header and one group",
+			stdout.String())
+	}
+
+	want := kept[0] + "\t" + kept[1] + "\t1\t300\t"
+	if !strings.HasPrefix(lines[1], want) {
+		t.Errorf("group = %q, want it to start %q", lines[1], want)
+	}
+
+	skipped := "scan: skipped " + excluded + " (--exclude)\n"
+	if got := stderr(); !strings.Contains(got, skipped) {
+		t.Errorf("stderr = %q, want it to contain %q", got, skipped)
+	}
+}
+
+func TestRunDwimTakesScanFlags(t *testing.T) {
+	// The dwim command parses and checks the scan flags as scan does.
+	// Each case stops before the walk of / begins, and before the
+	// database is created. "dwim --exclude /" excludes its own operand.
+	cases := map[string]struct {
+		args []string
+		code int
+		want string
+	}{
+		"--exclude /": {
+			[]string{cmdDwim, excludeFlag, "/"},
+			exitFatal,
+			"sfdupes: scan /: operand excluded by --exclude /\n",
+		},
+		"--exclude empty": {
+			[]string{cmdDwim, excludeFlag, ""},
+			exitUsage,
+			"Error: --exclude must not be empty\n",
+		},
+		"--workers 0": {
+			[]string{cmdDwim, workersFlag, "0", "-x", "--no-default-excludes"},
+			exitUsage,
+			"Error: --workers must be at least 1, got 0\n",
+		},
+	}
+
+	for name, tc := range cases {
+		t.Run(name, func(t *testing.T) {
+			path := testDBPath(t)
+			t.Setenv(databaseEnv, path)
+
+			stdout := captureStdout(t)
+			stderr := captureStderr(t)
+
+			code := run(tc.args, os.Stdout, os.Stderr)
+			if code != tc.code {
+				t.Errorf("run(%q) = %d, want %d", tc.args, code, tc.code)
+			}
+
+			if !strings.HasSuffix(stderr(), tc.want) || stdout() != "" {
+				t.Errorf("stdout, stderr = %q, %q, want \"\" and stderr "+
+					"ending %q", stdout(), stderr(), tc.want)
+			}
+
+			_, err := os.Lstat(path)
+			if !errors.Is(err, os.ErrNotExist) {
+				t.Errorf("lstat %s: %v, want no database", path, err)
+			}
+		})
+	}
+}
+
+func TestRunDwimHelpListsScanFlags(t *testing.T) {
+	t.Parallel()
+
+	// README "Subcommands" shows this usage line for dwim.
+	const want = "\n  sfdupes dwim [--workers N] [-x] [--no-default-excludes] " +
+		"[--exclude PATH]...\n"
+
+	var stdout, stderr bytes.Buffer
+
+	run([]string{cmdDwim, "-h"}, &stdout, &stderr)
+
+	if !strings.Contains(stderr.String(), want) {
+		t.Errorf("dwim -h stderr = %q, want the usage line %q",
+			stderr.String(), want)
+	}
+
+	if !strings.Contains(stderr.String(), excludeFlag+" PATH") {
+		t.Errorf("dwim -h stderr = %q, want %s PATH", stderr.String(),
+			excludeFlag)
+	}
+
+	// README "Settings": the help lists the default excludes and the
+	// filesystem types the walk never records anything on.
+	help := strings.TrimSpace(defaultExcludesHelp(runtime.GOOS))
+	if !strings.Contains(stderr.String(), help) {
+		t.Errorf("dwim -h stderr = %q, want it to hold %q", stderr.String(),
+			help)
+	}
+}
@@ -254,7 +254,7 @@ func readMountInfo(mountinfo io.Reader) (map[uint64]string, error) {
 	return devices, lines.Err()
 }

-// defaultExcludesHelp describes, for the scan command's help, the
+// defaultExcludesHelp describes, for the scan and dwim help, the
 // default excludes of the system goos names and, where the scan lists
 // the mounted filesystems, the types it never records anything on.
 func defaultExcludesHelp(goos string) string {
@@ -98,17 +98,16 @@ func scanPhase(name string) string {
 // runs, and the lock is released after it. When ctx is cancelled, as by
 // the SIGINT or SIGTERM that interruptContext catches, the scan keeps
 // what it has hashed (see syncScan), prints how many files its walk
-// reached, and returns errInterrupted. workers must be at least 1; the
-// scan command rejects anything less. Before the lock is taken, the
-// scan lists the filesystems that are not persistent, on which the walk
-// records nothing; unless noDefaultExcludes is set, the walk does not
-// enter the default excludes either. The walk neither enters nor
-// records the paths in excludePaths, the --exclude values; an operand
-// at or below one is a fatal error. Once the database is open, the scan
-// notes its files, which the walk passes over.
-func runScan(ctx context.Context, roots []string, workers int,
-	oneFS, noDefaultExcludes bool, excludePaths []string,
-) error {
+// reached, and returns errInterrupted. opts.workers must be at least 1;
+// the scan and dwim commands reject anything less. Before the lock is
+// taken, the scan lists the filesystems that are not persistent, on
+// which the walk records nothing; unless opts.noDefaultExcludes is set,
+// the walk does not enter the default excludes either. The walk neither
+// enters nor records the paths in opts.excludePaths, the --exclude
+// values; an operand at or below one is a fatal error. Once the
+// database is open, the scan notes its files, which the walk passes
+// over.
+func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
 		return err
@@ -123,7 +122,7 @@ func runScan(ctx context.Context, roots []string, workers int,

 	var rules walkRules

-	rules.excludePaths, err = excludePathInodes(excludePaths)
+	rules.excludePaths, err = excludePathInodes(opts.excludePaths)
 	if err != nil {
 		return fmt.Errorf("--exclude: %w", err)
 	}
@@ -138,7 +137,7 @@ func runScan(ctx context.Context, roots []string, workers int,
 		return fmt.Errorf("list the mounted filesystems: %w", err)
 	}

-	if !noDefaultExcludes {
+	if !opts.noDefaultExcludes {
 		rules.defaultExcludes = defaultExcludes(runtime.GOOS)
 	}

@@ -167,7 +166,7 @@ func runScan(ctx context.Context, roots []string, workers int,
 		return err
 	}

-	st, err := syncScan(ctx, db, roots, workers, oneFS, rules)
+	st, err := syncScan(ctx, db, roots, opts.workers, opts.oneFS, rules)
 	if errors.Is(err, context.Canceled) {
 		return interrupted(st.walked)
 	}
@@ -2196,7 +2196,7 @@ func TestScanHashWriteFailureUnwindsPool(t *testing.T) {
 	var stderr bytes.Buffer

 	code := run([]string{
-		cmdScan, "--workers", strconv.Itoa(hashLeakWorkers), dir,
+		cmdScan, workersFlag, strconv.Itoa(hashLeakWorkers), dir,
 	}, io.Discard, &stderr)
 	if code != exitFatal {
 		t.Fatalf("run(scan) = %d, want %d; stderr: %s",