sponge - soak up standard input and write to a file
sed '...' file | grep '...' | sponge file
sponge reads standard input and writes it out to the specified file.
Unlike a shell redirect, sponge soaks up all its input before opening
the output file. This allows constricting pipelines that read from and
write to the same file.
If no output file is specified, sponge outputs to stdout.
Colin Watson and Tollef Fog Heen
2006-02-19 sponge(1)