Core · Module 5 · Lesson 6 of 12

Descriptor Duplication and Redirection with dup and dup2

Master file descriptor duplication, redirect standard streams atomically with dup2, and preserve I/O state across processes.

ProAbout 16 minutes

By the end you can

Duplicate file descriptors to target identical Open File Descriptions using dup and dup2
Implement standard stream redirection (stdout/stderr) for shell pipelines
Explain the race condition eliminated by the atomicity guarantee of dup2
Preserve and restore standard streams using temporary descriptor backups

Builds on Standard I/O Buffering vs System Calls.

01 · A question first

How does a Unix shell redirect program output to a file when you run `./app > out.txt`, even though ./app hardcodes calls to printf() targeting file descriptor 1? The answer lies in remapping process descriptor slots using dup2.

Make a guess before you read on.

02 · The idea

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What's inside

Start with the problem
How the idea works
Why it is correct
What it costs
Pitfalls and variations
Where it is used