NAME¶

wasm-reduce - Reduce a wasm file to a smaller one with the same behavior on a given command.

DESCRIPTION¶

================================================================================ wasm-reduce INFILE

Reduce a wasm file to a smaller one with the same behavior on a given command.

Typical usage:

: wasm-reduce orig.wasm '--command=bash a.sh' --test t.wasm --working w.wasm

The original file orig.wasm is where we begin. We then repeatedly test a small reduction of it by writing that modification to the 'test file' (specified by '--test'), and we run the command, in this example 'bash a.sh'. That command should use the test file (and not the original file or any other one). Whenever the reduction works, we write that new smaller file to the 'working file' (specified by '--working'). The reduction 'works' if it correctly preserves the behavior of the command on the original input, specifically, that it has the same stdout and the result return code. Each time reduction works we continue to reduce from that point (and each time it fails, we go back and try something else).

As mentioned above, the command should run on the test file. That is, the first thing that wasm-reduce does on the example above is, effectively,

: cp orig.wasm t.wasm bash a.sh

In other words, it copies the original to the test file, and runs the command. Whatever the command does, we will preserve as we copy progressively smaller files to t.wasm. As we make progress, the smallest file will be written to the working file, w.wasm, and when reduction is done you will find the final result there.

Comparison to creduce:

1. creduce requires the command to return 0. wasm-reduce is often used to reduce

: crashes, which have non-zero return codes, so it is natural to allow any return code. As mentioned above, we preserve the return code as we reduce.

2. creduce ignores stdout. wasm-reduce preserves stdout as it reduces, as part

: of the principle of preserving the original behavior of the command (if your stdout varies in uninteresting ways, your command can be a script that runs the real command and captures stdout to /dev/null, or filters it).

3. creduce tramples the original input file as it reduces. wasm-reduce never

: modifies the input (to avoid mistakes that cause data loss). Instead, when reductions work we write to the 'working file' as mentioned above, and the final reduction will be there.

4. creduce runs the command in a temp directory. That is safer in general, but

: it is not how the original command ran, and in particular forces additional work if you have multiple files (which, for wasm-reduce, is common, e.g. if the testcase is a combination of JavaScript and wasm). wasm-reduce runs the command in the current directory (of course, your command can be a script that changes directory to anywhere else).

Source file:	wasm-reduce.1.en.gz (from binaryen 131-2)
Source last updated:	2026-08-02T23:38:50Z
Converted to HTML:	2026-08-03T02:47:01Z