chltam/pipex

pipex

Check

use valgrind --track-fds=yes to check if all fds are properly closed.

check memory leak when error encountered.

Fact

every process has their own file descriptor system, including STDIN and STDOUT

open("file", O_CREAT | O_WRONLY | O_TRUNC) is the same as creat("file")

pipe()

first initialize a int fd[2], then make it a pipe pipe(fd)

the pipe is a ONE way communication tool.

fd[0] refers to the read end of the pipe. (IN)

fd[1] refers to the write end of the pipe. (OUT)

pipe() returns 0 on success, returns -1 on error.

fork()

fork() returns the child pid in parent process, returns 0 in the child process

##dup2()

dup2(fd[1], STDOUT_FILENO) redirect the stdout to fd[1], so whatever originally output to the terminal(stdout) will go to the pipe.

execve

exec family replace the process image, statment after exec will only be executed in case of error

if (execve(SOMETHING) == -1)
  perror("error");

access()

int access(const char *pathname, int mode);

F_OK check for the existence of the file

W_OK R_OK X_OK check for write, read and execute permission respectively

access return 0 on success, -1 when fail for mode check (the file does not exist when F_OK is flagged)

Useful link

https://blog.csdn.net/wh128341/article/details/125906940 dup2 redirection, fd system, linux file system, inode, hard soft link, hard disk principle, (Chinese)