Using the same file for stdin and stdout with redirection

Question

I\'m writing a application that acts like a filter: it reads input from a file (stdin), processes, and write output to another file (stdout). The input file is completely re

Answer 1

There's a sponge utility in moreutils package:

./myprog < file.txt | sponge file.txt

To quote the manual:

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 constructing pipelines that read from and write to the same file.