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Lower-case, dash-separated filenames

Uses: Filename → Filename · Works on: copied local files with useful existing names · Time: about 5 minutes for a small batch · Undo: recorded renames in the current desktop session; keep originals

The problem

You want a consistent lowercase filename stem with hyphens instead of spaces or underscores. Keep the mixed-case title in the tag: a filename policy does not need to become a metadata policy. This can be useful for an established transfer or naming convention, but it does not certify compatibility with a particular website, USB device or filesystem.

Existing filename Expected destination
03 Paper Boats.mp3 03-paper-boats.mp3
04_Lanterns On The Water.flac 04-lanterns-on-the-water.flac
05 Café At Low Tide.MP3 05-café-at-low-tide.MP3
06 Paper Boats.mp3 06-paper--boats.mp3

The converter retains the original audio extension, including its spelling. The third example lowers the stem while keeping .MP3. Accents remain; this is not an ASCII-only or accent-removal recipe. The last row deliberately shows that replacing individual spaces can produce repeated hyphens.

The solution

  1. Keep the originals elsewhere and select a few copied local audio files. Save or discard pending tag edits before renaming. If a filter is active, inspect the intended selection, including any previously selected hidden rows.
  2. Choose Convert → Filename → Filename….

  3. Set Old filename pattern to:

    %1

  4. Set New filename pattern to:

    $lower($replace(%1, ,-,_,-))

  5. Choose Preview. Compare every full destination with the table and your actual folder contents. The single space after the first comma is the search text; it must remain a real space in the expression.

  6. Choose Rename … files only for the reviewed small plan. Inspect the operation result, the actual destination names and the unchanged tag fields.

Paths change when the rename runs. There is no subsequent Save tags step for these names. Editing an input or changing the selection requires another preview; an expired plan or changed file can also require it. A preview is not a reservation of the destination.

How it works

The old pattern %1 captures the current basename without the audio extension. It is a numbered capture, with no trailing percent sign: %1% is not the same syntax. It does not read TITLE or ARTIST.

Read the new pattern from the inside out:

Part Meaning
%1 Reuse the captured basename
$replace(%1, ,-,_,-) Replace each ordinary space with -, then each underscore with -
$lower(...) Lowercase the resulting text

Commas separate function arguments. The first pair has a space as its search string and a hyphen as its replacement. The second pair does the same for _. Existing hyphens, punctuation and non-ASCII letters are not removed by those replacements. Tabs are not ordinary spaces either.

This route works from names even if the title tags are empty. It does not lowercase tags or rename the parent album folder. To derive names from reviewed tags instead, use the variation below and its different converter.

Variations

Collapse runs of spaces, underscores and hyphens

If repeated hyphens are unwanted, keep Old filename pattern %1 and use:

$lower($regexp(%1,'[ _-]+',-))

For 06 Paper Boats.mp3, this produces 06-paper-boats.mp3. [ _-]+ matches one or more ordinary spaces, underscores or hyphens; putting the hyphen last makes it literal in that character class. This also collapses an intentionally doubled hyphen. It does not trim a leading/trailing separator or normalize all Unicode whitespace.

Derive a name from saved tags

When TRACK = 3/8 and TITLE = Paper Boats, use Tag → Filename… instead, with:

$num(%track%,2)-$lower($replace(%title%, ,-,_,-))

For an MP3 this gives 03-paper-boats.mp3. This route reads the tags, not the captured old basename. Check missing titles, nonnumeric tracks and multi-value fields before applying it. $num reads a leading number; it does not preserve a vinyl-side label such as B2.

Keep the original spelling when case is significant

Remove the outer $lower(...) and use only the replacement expression. That is a different naming policy, useful when deliberate capitals matter. Do not rename a larger set merely because lowercase looked acceptable in one example. A case-only spelling change can behave differently on different volumes; check the actual operation result and the name your file manager shows.

Before using the result elsewhere

Two different names can collapse to one destination after lowercasing or separator replacement. Include an established distinguishing track/disc part and compare the complete paths. Do not delete another file to make a refused rename succeed. If the only intended change is capitalization, try one copy first on the actual destination volume rather than treating it as proof for every platform.

A lowercase name can still be too long or contain characters a receiving system dislikes. Follow the portable-name recipe for a more explicit character and length policy. Test the resulting copies on the receiving device; a successful rename is not a playback test.

Use Edit → Undo and its operation label for recorded renames in the current desktop session. Keep original copies for recovery after quitting.