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comment on how pipe work

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Night Kaly 2024-02-09 17:20:38 +00:00
parent b171d3ab22
commit a058bd3ae8
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GPG key ID: 8E829D3381CFEBBE
1 changed files with 8 additions and 13 deletions
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21
commands.c
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@ -203,7 +203,6 @@ int execute_pipe(char ***args) {
int pipefd[2]; int pipefd[2];
int status; int status;
pid_t pid; pid_t pid;
int i = 0;
int in = 0; int in = 0;
int num_cmds = 0; int num_cmds = 0;
@ -214,22 +213,24 @@ int execute_pipe(char ***args) {
for (int i = 0; i < num_cmds - 1; i++) { for (int i = 0; i < num_cmds - 1; i++) {
pipe(pipefd); pipe(pipefd);
if ((pid = fork()) == 0) { if ((pid = fork()) == 0) {
dup2(in, 0); // change input according to the old one // then this (child)
dup2(in, STDIN_FILENO); // get input from previous command
if (i < num_cmds - 1) { if (i < num_cmds - 1) {
dup2(pipefd[1], 1); // change output to the input of the next command dup2(pipefd[1], STDOUT_FILENO); // make output go to pipe (next output)
} }
close(pipefd[0]); close(pipefd[0]); // close original input
status = execute(args[i]); status = execute(args[i]);
exit(status); exit(status);
} else if (pid < 0) { } else if (pid < 0) {
perror("fork failed"); perror("fork failed");
} }
close(pipefd[1]); // this will be executed first
in = pipefd[0]; close(pipefd[1]); // close output
in = pipefd[0]; // save the input for the next command
} }
if ((pid = fork()) == 0) { if ((pid = fork()) == 0) {
dup2(in, 0); dup2(in, STDIN_FILENO); // get input from pipe
status = execute(args[num_cmds - 1]); status = execute(args[num_cmds - 1]);
exit(status); exit(status);
} else if (pid < 0) { } else if (pid < 0) {
@ -240,11 +241,5 @@ int execute_pipe(char ***args) {
for (int i = 0; i < num_cmds; i++) { for (int i = 0; i < num_cmds; i++) {
wait(&status); wait(&status);
} }
return 1; return 1;
} }