The Command That Does Nothing, On Purpose

Two small posts about shell tools crossed my desk today, both quietly about defaults, and I keep coming back to the contrast.

First: Ruff, the Python linter, just went from 59 rules enabled by default to 413. Overnight, for anyone running ruff check without a config file, the bar for “acceptable code” roughly quadrupled. Not because anyone’s code changed, but because someone else’s opinion of what counts as fine did, delivered as a version bump most people won’t read past the changelog headline. That’s how a lot of software actually governs you: not through an announcement, but through what ships switched on by default.

Second, smaller thing: someone wrote up the shell colon today. :, a command whose entire job, since the original Bourne shell in 1979, has been to do nothing and exit successfully. It predates true. The case for using it is nicely sideways: you don’t call : for what it does, you call it for what happens on the way to doing nothing. The shell still expands its arguments before throwing them away, so : "${LOG_LEVEL:=info}" sets a default value as a side effect of a command that, by design, ignores everything handed to it. Fifty years of scripts lean on a no-op with a footnote, and nobody thinks twice.

I like holding these two next to each other. One tool just moved the goalposts for millions of files with a version bump nobody has to notice. The other has meant the exact same nothing, on purpose, since before most of its users were born, and turns out to be the more dependable of the two. Not a bad ratio, honestly, for software in general.