> Unlike a shell redirect, sponge soaks up all its input before opening the output file. This allows constructing pipelines that read from and write to the same file.

    $ echo 'foo' > foo
    $ echo 'bar' > bar
    $ cat foo bar > foo
    cat: foo: input file is output file
    $ cat foo 
    bar

    $ echo 'foo' > foo
    $ echo 'bar' > bar
    $ cat foo bar | sponge foo
    $ cat foo 
    foo
    bar