Unix Command Internals

Redirection

ps just writes to its standard output as before, but now the data goes into the file
- But ps doesn't have to know or care
The shell does it all
This is how pipes are set up also
For ps | grep the shell forks twice
- It tampers with the open file tables before execing ps and grep
- ps and grep don't have to know or to care
inetd pulls a similar trick to attach a process's standard input and output to a network socket