`find -delete` before `-name` deletes everything

This looks like it deletes one temp file. It deletes the whole directory, including the directory itself:

mkdir demo
touch demo/keep.txt demo/old.tmp

find demo -delete -name '*.tmp'

ls demo
# ls: cannot access 'demo': No such file or directory

That's GNU findutils 4.10.0. There's no prompt and no warning. keep.txt is gone.

Why it happens

find doesn't treat its arguments as a list of options. It evaluates them as an expression, from left to right, for each file. So the command above means:

1. Delete this file.
2. Then check whether its name matches *.tmp.

By the time -name runs, the damage is done. -delete isn't a setting that applies to whatever matched. It's an action that runs at the point where you wrote it.

The man page says this outright:

Warning: Don't forget that find evaluates the command line as an expression, so putting -delete first will make find try to delete everything below the starting points you specified.

The safe version

Run it with -print first, then swap in -delete as the last thing on the line:

mkdir demo
touch demo/keep.txt demo/old.tmp

find demo -name '*.tmp' -print
# demo/old.tmp

find demo -name '*.tmp' -delete

ls demo
# keep.txt

The same order rule applies to -exec. Filters go first, and the action goes last.

What's the worst thing a command with the arguments in the wrong order has done to you?