Pipex

A C program that replicates what the shell does when you write < infile cmd1 | cmd2 > outfile. Two child processes, one pipe, file descriptor redirections, and execve calls. The result is functionally identical to the shell version.

Usage

./pipex infile "cmd1" "cmd2" outfile
# same as: < infile cmd1 | cmd2 > outfile
 
./pipex input.txt "grep hello" "wc -l" output.txt

Bonus - multiple pipes:

./pipex infile "cmd1" "cmd2" "cmd3" outfile
# same as: < infile cmd1 | cmd2 | cmd3 > outfile

Bonus - heredoc:

./pipex here_doc LIMITER "cmd1" "cmd2" outfile
# same as: cmd1 << LIMITER | cmd2 >> outfile

How it works

[infile] --> [child1: cmd1] --pipe--> [child2: cmd2] --> [outfile]
                   |                        |
                 fork()                   fork()
                   +-------- parent -------+
                                 |
                             waitpid()

1. Parent opens infile and outfile
2. Creates a pipe (read end and write end)
3. Child 1 redirects stdin from infile, stdout to the pipe write end, runs cmd1
4. Child 2 redirects stdin from the pipe read end, stdout to outfile, runs cmd2
5. Parent waits for both

Commands are looked up from $PATH.

Errors