Replacing files in place

Sometimes you want to optimize files in place — no _timestamp copies, no separate output directory. That’s what --replace is for, and it’s designed to be safe.

Basic usage

imgsqz photo.jpg --replace -q 80

This re-encodes photo.jpg and writes the smaller result back to photo.jpg.

How it stays safe (atomic writes)

A naive “overwrite in place” is dangerous: if the process dies mid-write, you’re left with a truncated, corrupt file. imgsqz avoids this:

1. Encode the optimized image to a temporary file next to the target: photo.jpg.imgsqz.tmp.
2. Once the temp file is fully written, atomically rename it over the original (fs.rename).

A rename is atomic on a single filesystem, so at no point is photo.jpg a half-written file. If imgsqz is interrupted before step 2, your original is untouched — you just have a stray .imgsqz.tmp you can delete.

It's still a destructive edit

--replace permanently changes your source files. Re-compressing an already-lossy image again degrades quality further (generation loss). For irreplaceable originals, optimize to a copy (the default behavior) instead.

Replacing while converting

--replace keeps the file in place but the extension follows the format. If you convert, you get a new file alongside the original name pattern:

# Re-encode and keep as JPG, in place
imgsqz photo.jpg --replace -q 78

# "Replace" but convert to webp → writes photo.webp (the .jpg still exists)
imgsqz photo.jpg --replace -f webp

Note

--replace only truly overwrites when the output format matches the source extension. When converting to a different format, the output is a different filename (photo.webp), so the original photo.jpg remains. To remove the original after a converting batch, delete the sources yourself once you’ve verified the results.

Batch replace

--replace works across many inputs (unlike --output):

# Optimize every JPG in place
imgsqz *.jpg --replace -q 80 --quiet

This is the canonical “shrink this whole folder of photos in place” command.

Replace vs. the alternatives

Goal	Command
Keep original, make a timestamped copy (default)	imgsqz photo.jpg
Keep original, clean output name	imgsqz photo.jpg --no-timestamp -o photo-opt.jpg
Overwrite the original in place	imgsqz photo.jpg --replace
Write to a separate folder	imgsqz photo.jpg -o out/photo.jpg

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Next: the full CLI reference.