【发布时间】：2019-09-23 17:31:45
【问题描述】：
我正在尝试创建一个辅助类来执行系统命令并通过管道支持获得响应。对于我只需要获取响应的情况（命令没有 STDIN 消耗），它按预期工作，对于管道支持，我的 STDIN 出现乱码，我找不到根本原因。
处理这个机制的主要函数是（请忽略小错误检查问题）
最小的工作示例
#include <vector>
#include <string>
#include <iostream>
#include <sstream>
#include <unistd.h>
#include <sys/prctl.h>
#include <sys/types.h>
#include <signal.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <stdarg.h>
struct exec_cmd_t {
exec_cmd_t(std::vector<std::string> args) : args(args), has_executed(false), cpid(-1) { }
exec_cmd_t(const exec_cmd_t &) = delete;
exec_cmd_t(exec_cmd_t &&) = delete;
exec_cmd_t & operator=(const exec_cmd_t &) = delete;
exec_cmd_t & operator=(exec_cmd_t &&) = delete;
std::string operator()();
std::string pipe_cmd(const std::string & input);
std::string pipe_cmd();
~exec_cmd_t();
private:
std::vector<std::string> args;
bool has_executed;
int cpid;
std::stringstream in_stream;
std::stringstream out_stream;
friend std::string operator | (exec_cmd_t & first, exec_cmd_t & second);
friend std::string operator | (exec_cmd_t && first, exec_cmd_t && second);
friend std::string operator | (std::string, exec_cmd_t & second);
friend std::string operator | (std::string, exec_cmd_t && second);
};
std::string exec_cmd_t::pipe_cmd(const std::string & input) {
this->has_executed = true;
const int read_end = 0;
const int write_end = 1;
int read_pipe[2];
int write_pipe[2];
if (pipe(read_pipe) < 0 || pipe(write_pipe) < 0) {
this->has_executed = false;
return std::string{};
}
this->in_stream << input;
std::string line;
while(getline(this->in_stream, line)) {
if (line.size() == 0) {
continue;
}
int wr_sz = write(write_pipe[write_end], line.c_str(), line.size());
if (wr_sz <= 0) {
break;
}
write(write_pipe[write_end], "\n", 1);
}
close(write_pipe[write_end]);
this->cpid = fork();
if (this->cpid == 0) {
dup2(write_pipe[read_end], STDIN_FILENO);
dup2(read_pipe[write_end], STDOUT_FILENO);
close(read_pipe[read_end]);
close(write_pipe[write_end]);
close(read_pipe[write_end]);
close(write_pipe[read_end]);
prctl(PR_SET_PDEATHSIG, SIGTERM);
char * params[args.size()];
const char * image_path = args[0].c_str();
for(int i = 1; i < args.size(); i++) {
params[i-1] = const_cast<char *>(args[i].c_str());
}
params[args.size()] = nullptr;
execv(image_path, params);
exit(1);
}
close(read_pipe[write_end]);
close(write_pipe[read_end]);
char buff[256];
int rd_sz = -1;
int flags = fcntl(read_pipe[0], F_GETFL, 0);
fcntl(read_pipe[read_end], F_SETFL, flags | O_NONBLOCK);
int status = 0;
waitpid(this->cpid, &status, 0);
this->has_executed = false;
int error_code = 0;
while((rd_sz = read(read_pipe[read_end], buff, sizeof(buff))) > 0) {
buff[rd_sz] = '\0';
this->out_stream << std::string{buff};
}
close(read_pipe[read_end]);
return this->out_stream.str();
}
std::string exec_cmd_t::pipe_cmd() {
static std::string empty_str{};
return pipe_cmd(empty_str);
}
std::string exec_cmd_t::operator()() {
return pipe_cmd();
}
exec_cmd_t::~exec_cmd_t() {
if (this->has_executed) {
int status;
waitpid(this->cpid, &status, WNOHANG);
if (!WIFEXITED(status)) {
kill(this->cpid, SIGKILL);
waitpid(this->cpid, &status, 0);
}
}
}
std::string operator | (exec_cmd_t & first, exec_cmd_t & second) {
return second.pipe_cmd(first());
}
std::string operator | (exec_cmd_t && first, exec_cmd_t && second) {
return second.pipe_cmd(first());
}
std::string operator | (std::string output, exec_cmd_t & second) {
return second.pipe_cmd(output);
}
std::string operator | (std::string output, exec_cmd_t && second) {
return second.pipe_cmd(output);
}
int main() {
auto str = exec_cmd_t{ {"/bin/echo", "echo", "hello\nworld\nor\nnot"} } | exec_cmd_t{ {"/bin/grep", "grep", "world", "-"} };
std::cout << str << std::endl;
return 0;
}
给我
grep: =V: No such file or directory
(standard input):world
似乎 grep 执行了两次，一次失败，没有这样的文件或目录，另一次成功。任何建议都会非常有帮助:-)。 提前致谢。
【问题讨论】：
-
您的代码似乎是 C++，因此您应该删除 C 标记。您的代码不完整。请显示足够的代码，以便我们编译并重现问题。
-
是的，我认为您不应该过滤掉管道中的任何内容：ing。当您在实际代码中使用它并期待空白行时，以后可能会感到困惑。
-
@TedLyngmo 同意了。谢谢你的建议:-)
-
@TedLyngmo 好点，谢谢我会在测试后更新结果。
-
好的，我打算自己尝试一下您的代码，但它似乎缺少某些部分。你能不能把minimal reproducible example放在一起？看起来很有趣。