Pipes, Redirection, and File Descriptors

1-dup.c

• Opens cats.txt and redirects stdout to that file using dup2.
• Writes "cat 1" with write(), then "cat 2" with printf().

Question: What ends up inside cats.txt after running this program?

2-dup2.c

• Opens cats.txt in append mode (so you don’t overwrite the existing content).
• Redirects stdout to the file.
• Prints "cat 3".

Question: After this, what does cats.txt contain?

3-copy.c

• Opens cats.txt for reading and dogs.txt for writing.
• Copies content byte by byte using read() and write().

Question: Why do we need two loops to write? When does bytesRead not return 1024 (the size of the buffer)?

4-pipe-one-process.c

• Creates a pipe inside a single process.
• Writes "meow" into the pipe, then reads it back.

Question: What happens if you try to read() again after the pipe is empty?

5-redirect.c

• Redirects stdin from scores.csv and stdout to out.txt.
• Executes:

grep niko < scores.csv > out.txt

Question: grep reads from stdin and writes to stdout. How do we change grep’s behavior to read from scores.csv and write to out.txt without changing grep’s code?

6-pipe-ls-wc.c

• Implements:

  ls -l | wc -l

• Two children: one runs ls, the other runs wc.

Question: Does it matter if ls runs before wc or wc runs before ls?

7-pipe-parent-child.c

• Parent writes "meow" into the pipe.
• Child reads and prints "From parent: meow".

Question: What happens if the parent does not close the write end after writing?

8-pipe-chain.c

• Implements:

  cat scores.csv | grep niko | cut -f2 -d','

• Three processes chained by two pipes.

Questions

1. Which process reads from p1, which writes to p2?
2. What is the final output if scores.csv contains a line with "niko,95"?