pipex

how to clone:

git clone git submodule init git submodule update

or git clone --recurse-submodules

execution:

./pipex file1 "cmd1" "cmd2" file2

works as this command shell: $> < file1 cmd1 | cmd2 > file2

idea

father process will have two child, each one will execute the first and the second command correspondingly. the father then will wait those interconnected process by a pipe to finish, and then exit the program accordingly.

how a pipe works

res = pipe(fd[2])

when a pipe is opened, the resulting file descriptors open are fd[0] and fd[1]:

• fd[0] where you read from
• fd[1] where you write into

how dup2 works

int dup2(int oldfd, int newfd)

oldfd is where you will be taking information, and the newfd is what fd you are substituting

e.g. fd = open("file", O_RDONLY); -> file to read from as if it was STDIN dup2(fd, STDIN_FILENO); -> replace stdin with the new file descriptor close(fd); -> close the old and duplicated file descriptor exec(...); -> now the program executed on this new process will read from the file instead of the user input from the keyboard as usual

classic executions for testing

• ./pipex /dev/fd/0 cat ls /dev/fd/1 -> checks if 'wait()' functions are done in the father process -> should let you input on stdin and then close

• ./pipex Makefile "" ls /dev/fd/1 -> checks if the null command doesn't segfault the program, and then outputs through stderr the invalid command (as in bash) -> should input the ls -> $? = 0

• ./pipex Makefile ls clkdsj outfile -> print on stderr that the command do not exist -> create the outfile (no matter if the second command failed) -> error code ($?) must be 127

• ./pipex here_doc LIM cat ls outfile -> make sure the outfile is APPENDED and not TRUNCATED