ezyang's blog

Raise your hand if you’ve ever put one of these commands in your continuous integration scripts:

• apt install somepackage
• pip install -r requirements.txt or pip install somepkg
• conda install blah
• cabal update or cabal install blah
• git clone https://github.com/someguy/somerepo
• wget http://some-website/thingy-latest.tgz

Can you tell what the problem is? These commands are not reproducible: depending on when you run them, they may give different results. More insidiously, most of the time they give you the same result (or, perhaps, a different result that still works for your use case).

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