[英]Redirection of child process Standard Output to pipe in C
我嘗試理解將子進程“標准輸出”重定向到管道的主題,即父進程可以讀取它並面對非常奇怪的行為。 在示例父進程fork 3的子進程中,它們執行簡單的文件搜索並希望獲得輸出。 我只收到第一個結果。 這個例子可能有什么問題?
代碼如下:
char * searches[] = {
".bashrc",
"NM34_x64.exe",
"blacklist.sh"
};
int fd[2];
if (pipe(fd) == -1) {
error("Can't create the pipe");
}
__pid_t pids[sizeof(searches)/sizeof(char*)];
for(int i = 0; i < sizeof(searches)/sizeof(char*); i++){
__pid_t pid = fork();
switch (pid) {
case -1 :
// ERROR CASE
error("Failed to make a child process");
break;
case 0 :
// CHILD CASE
// 1. Redirect Standard Output to pipe
dup2(fd[1], 1);
close(fd[0]);
// 2. Execute command
if (execl("/usr/bin/find", "/usr/bin/find", "/home", "-name", searches[i], NULL) == -1)
error("Failed to execute the command in the child process");
break;
default:
// PARENT CASE
printf("Created child process with pid %d\n", pid);
pids[i] = pid;
// 1. Wait for PID to finish
int status;
waitpid(pids[0], &status, 0);
if (status == -1)
error("Failed to wait the child PID");
printf("Process %d finish his work\n", pids[i]);
// 2. Redirect pipe to Standard Input
dup2(fd[0],0);
close(fd[1]);
// 3. Read Standard Input
char line[255];
while (fgets(line,255,stdin)) {
printf("%s", line);
}
break;
}
}
return 0;
這是輸出:
Created child process with pid 5063
Process 5063 finish his work
/home/user/.bashrc
Created child process with pid 5064
Process 5064 finish his work
Created child process with pid 5065
Process 5065 finish his work
當使用管道進行進程間通信時,直接從管道讀取輸入到主進程,而不是將其再次重定向到標准輸入並在主進程中讀取。
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