moreutils sponge?

[karlicoss]

Huh, ran into it here

sponge reads standard input and writes it out to the specified file. Unlike a shell redirect, sponge soaks up all its input before writing the output file. This allows constructing pipelines that read from and write to the same file. sponge preserves the permissions of the output file if it already exists. When possible, sponge creates or updates the output file atomically by renaming a temp file into place. (This cannot be done if TMPDIR is not in the same filesystem.)

So I guess requires TMPDIR hackery if you want to guarantee atomictity and using pipes