sponge () { tac|tac; } EDIT: this doesn't work for the "sed s/foo/bar/ file|sponge file" case, but it does for certain other usages where you basically want to

sponge () { tac|tac; } EDIT: this doesn't work for the "sed s/foo/bar/ file|sponge file" case, but it does for certain other usages where you basically want to wait until EOF before outputting