我正在尝试使用C实现此linux命令。 ls -l | cut -b 1
我试图这样做的方式是
在父进程中调用ls -l 将ls -l的输出放在一个文件中(写入文件)
在子进程中调用cut 读取文件(在父进程中写入的文件) 将剪切应用于文件 打印输出
这是迄今为止我所做的
/* pipe.c */
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
void main()
{
int filedes[2];
int p;
pid_t pid, pid1;
p=pipe(filedes);
FILE *stream;
char buff[20];
printf("pipe command returns %d, %d ,%d\n",p, filedes[0],filedes[1]);
if(pipe(filedes) == -1) /* Create the pipe */
printf("error pipe");
pid1=fork();
pid=getpid();
switch (pid1) { /* Create a child process */
case -1:
printf("error fork");
case 0: /* Child */
/* Close unused write end */
/* Child can now read from pipe */
if (close(filedes[1]) == -1)
printf("error close");
printf("I am a child process pid %d, and will read from pipe\n",pid);
while (read(filedes[0], &buff, 1) > 0)
write(STDOUT_FILENO, &buff, 1);
write(STDOUT_FILENO, "\n", 1);
close(filedes[0]);
_exit(EXIT_SUCCESS);
break;
default: /* Parent */
/* Close unused read end */
/* Parent can now write to pipe */
if (close(filedes[0]) == -1)
printf("error close");
printf("I am the parent process pid %d, and will write to pipe\n", pid );
stream = fdopen(filedes[1], "w");
strcpy(buff, "This is a test\n");
write(filedes[1], buff, strlen(buff));
char *args[80];
args[0] = "ls";
args[1] = "-l";
args[2] = NULL;
execvp(args[0],args);
int bak, new;
bak = dup(1);
new = open("/home/urwa/abc.txt", O_WRONLY);
dup2(new, 1);
close(new);
close(filedes[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
break;
}
}
这段代码完美无缺。并在展台上打印输出测试声明。以及ls -l输出。但文件是空的。我究竟做错了什么。 我也试过freopen如下..仍然是空文件。 :/
FILE *fp;
fp = freopen ("/temp/abc.txt", "a+", stdout);
答案 0 :(得分:0)
你没有在孩子中调用剪切,文件描述符也搞乱了。
要执行任务,您必须关闭父级的标准输出,并在execvp 之前使父级中的写入结束标准输出。在孩子中,您必须关闭孩子的stdin ,并在execvp 之前将读取结束作为stdin给您的孩子。以这种方式your parent's stdout is stdin of your child
(创建管道b / w两个)。
int main()
{
int filedes[2];
int p;
pid_t pid = 0, pid1 = 0;
p=pipe(filedes);
FILE *stream;
char buff[20];
char *args[80];
printf("pipe command returns %d, %d ,%d\n",p, filedes[0],filedes[1]);
if(pipe(filedes) == -1) /* Create the pipe */
printf("error pipe");
pid1=fork();
pid=getpid();
switch (pid1) { /* Create a child process */
case -1:
printf("error fork"); break;
case 0: /* Child */
/* Close unused write end */
/* Child can now read from pipe */
if (close(filedes[1]) == -1)
printf("error close");
printf("I am a child process pid %d, and will read from pipe\n",pid);
close(0); //close stdin of child
dup(filedes[0]); //make pipes read end stdin of child
args[0] = "cut";
args[1] = "-b";
args[2] = "1";
args[3] = NULL;
execvp(args[0],args);
break;
default: /* Parent */
/* Close unused read end */
/* Parent can now write to pipe */
if (close(filedes[0]) == -1)
printf("error close");
printf("I am the parent process pid %d, and will write to pipe\n", pid );
close(1); //close stdout
dup(filedes[1]); //make write end of pipe stdout of parent
args[0] = "ls";
args[1] = "-l";
args[2] = NULL;
execvp(args[0],args);
break;
}
}