c – 玩具外壳未正确配管
作者:互联网
我不会撒谎.这是一个家庭作业问题.但是,据我所知,这些点已经消失了.现在,我只是在寻找答案,因为我想 – 我可能会疯了.
该程序的目标是执行命令ps -A | grep(inputstring)| wc -l的方式类似于shell的方式.所以,我产生了进程,让它们互相等待.最新的进程,曾孙,execlp(“ps”,“ps”,“ – A”,NULL),用ps -A进程取而代之.在execlp之前,我确保它的标准输出转到管道输出.行中的下一个进程是wait()ing,并且已经自己设置,以便输入管道进入标准输入,标准输出进入输出管道,它将执行grep,依此类推.
我几乎是肯定的,我已经正确设置了它.然而……程序确实如此.不.工作.
#include <stdlib.h>
#include <iostream>
#include <string>
#define MAXLINE 1500
#define READ 0
#define WRITE 1
using namespace std;
int main( int argc, char** argv ) {
//* start of input block
if ( argc != 2 ) {
cout << "Usage: ./a.out arg1" << endl;
return 0;
}
string in = argv[1];
// end of input block */
int pipeA[2], pipeB[2], pid, stat;
// get our first set of pipes
if ( pipe(pipeA) < 0 ) {
cerr << "Pipe error.\n";
exit(-1);
}
if ( pipe(pipeB) < 0 ) {
cerr << "Pipe error.\n";
exit(-1);
}
// make the first fork
if ( (pid = fork() ) < 0 ) { cerr << "Fork error.\n"; exit(-1); }
if ( pid > 0 ) { // parent case
wait(&stat);
} else { // child case
if ( (pid = fork()) < 0 ) { cerr << "Fork Error\n"; exit(-1); }
if ( pid > 0 ) { // child
wait(&stat);
dup2(pipeA[READ],READ);
execlp("wc","wc","-l",NULL);
} else { // grand-child
if ( (pid = fork()) < 0 ) { cerr << "Fork Error\n"; exit(-1); }
if ( pid > 0 ) { // still grand-child
wait(&stat);
dup2(pipeB[READ],READ);
dup2(pipeA[WRITE],WRITE);
close(pipeB[READ]);
execlp("grep","grep",in.c_str(),NULL);
} else { // great grand-child
dup2(pipeB[WRITE],WRITE); // t now goes to pipeB[1]
close(READ);
close(pipeB[READ]);
execlp("ps", "ps", "-A", NULL);
}
}
}
return 0;
}
编辑:更改为我的代码的双管变体.
解决方法:
我几乎可以肯定这就是你要做的事情.为马虎编码提前道歉.它在这里有点晚了,我现在应该睡觉了:
#include <iostream>
#include <string>
#include <cstdlib>
#include <cstdio>
#include <unistd.h>
#define READ 0
#define WRITE 1
// ps -A | grep argv[1] | wc -l
int main( int argc, char** argv )
{
//* start of input block
if ( argc != 2 )
{
std::cout << "Usage: ./a.out arg1" << std::endl;
return 0;
}
// make local copy of argument
std::string in = argv[1];
int fd1[2], fd2[2], pid;
// allocate two pipe sets
if (pipe(fd1) < 0 || pipe(fd2) < 0)
{
perror("Failed to create pipe.");
return EXIT_FAILURE;
}
// launch first child process.
if ((pid = fork()) < 0)
{
perror("Failed to fork child(1)");
return EXIT_FAILURE;
}
if (pid == 0)
{
// wc -l process.
// stdin = fd2(read)
close(fd1[READ]);
close(fd1[WRITE]);
close(fd2[WRITE]);
dup2(fd2[READ],STDIN_FILENO);
execlp("wc","wc","-l",NULL);
}
// fork again. this time for grep
if ((pid = fork()) < 0)
{
perror("Failed to fork child(2)");
return EXIT_FAILURE;
}
if (pid == 0)
{
// grep argv[1] process.
// stdin = fd1(read)
// stdout = fd2(write)
close(fd1[WRITE]);
close(fd2[READ]);
dup2(fd2[WRITE], STDOUT_FILENO);
dup2(fd1[READ], STDIN_FILENO);
execlp("grep", "grep", in.c_str(), NULL);
}
// fork once more. this time for ps -A
if ((pid = fork()) < 0)
{
perror("Failed to fork child(3)");
return EXIT_FAILURE;
}
if (pid == 0)
{
// ps -A process.
// stdout = fd1(write)
close(fd2[WRITE]);
close(fd2[READ]);
close(fd1[READ]);
dup2(fd1[WRITE], STDOUT_FILENO);
execlp("ps", "ps", "-A", NULL);
}
int stat=0;
wait(&stat);
return EXIT_SUCCESS;
}
在我的系统上,ps -A报告了141行,其中41行中有单词System some within,只需运行ps -A | grep系统| wc -l.上面的代码生成完全相同的输出.
希望它可以帮助你.
标签:c,shell,process,dup2 来源: https://codeday.me/bug/20190928/1826063.html