在管道中获取命令输出，C for Linux [英] get command output in pipe, C for Linux

问题描述

我需要运行 Linux CLI 命令并从 C 中获取其标准输出.

我可以使用 pipe() 创建一个管道，然后 fork/exec，在调用 exec() 之前将 child 的 stdout 描述符重定向到管道中，并从 parent 中的管道中读取.另外我需要等孩子.

是否有一个简单的调用来做 fork + redirect + exec + wait，就像 system() 做 fork + exec + wait 一样，只有 system() 不做重定向.

有 popen()，它执行 fork + redirect + exec，但不执行等待，所以我无法获得退出状态.

解决方案

是这样吗?

<前>姓名popen, pclose - 处理 I/O概要#include FILE *popen(const char *command, const char *type);int pclose(FILE *stream);描述popen() 函数通过创建管道、分叉、并调用外壳.由于管道根据定义是单向的，因此类型参数只能指定读或写，不能同时指定；所结果的流相应地是只读或只写的.命令参数是指向以空字符结尾的字符串的指针包含一个 shell 命令行.此命令传递到/bin/sh使用 -c 标志；解释(如果有的话)由外壳程序执行.类型参数是一个指向空终止字符串的指针，该字符串必须是r"代表阅读，w"代表写作.popen() 的返回值是一个普通的标准 I/O 流除了它必须用 pclose() 而不是 fclose() 关闭之外，所有方面都除外.写入这样的流会写入命令的标准输入；这命令的标准输出与调用的进程的标准输出相同popen()，除非它被命令本身改变了.反过来读从popened"流读取命令的标准输出，然后命令的标准输入与调用的进程的标准输入相同弹出().请注意，默认情况下输出 popen() 流是完全缓冲的.pclose() 函数等待关联进程终止并返回 wait4() 返回的命令退出状态.

I need to run a Linux CLI command and get its stdout output from C.

I can use pipe() to create a pipe, then fork/exec, redirecting child's stdout descriptor into the pipe before calling exec(), and reading from the pipe in parent. Plus I'll need to wait on the child.

Is there a simple call to do fork + redirect + exec + wait, like system() does fork + exec + wait, only system() doesn't do the redirect.

There's popen(), which does fork + redirect + exec, but doesn't do wait, so I can't get exit status.

解决方案

Is this it?

NAME
       popen, pclose - process I/O

SYNOPSIS
       #include <stdio.h>  

       FILE *popen(const char *command, const char *type);

       int pclose(FILE *stream);

DESCRIPTION
       The  popen()  function opens a process by creating a pipe, forking, 
and invoking the shell.  Since a pipe is by definition unidirectional, the 
type argument may specify only reading or writing, not both; the resulting 
stream is correspondingly read-only or write-only.

       The command argument is a pointer to a null-terminated string 
containing a shell command line.  This command is passed to /bin/sh 
using the -c flag; interpretation, if any, is performed by the shell.  
The type argument is a pointer to a null-terminated string which must be 
either ‘r’ for reading or ‘w’ for writing.

       The  return  value  from popen() is a normal standard I/O stream in 
all respects save that it must be closed with pclose() rather than fclose().  
Writing to such a stream writes to the standard input of the command; the 
command’s standard output is the same as that of the process that called 
popen(), unless this is altered by the command itself.  Conversely, reading 
from a ‘‘popened’’ stream reads the command’s standard output, and the 
command’s standard input is the same as that of the process that called 
popen().

       Note that output popen() streams are fully buffered by default.

       The pclose() function waits for the associated process to terminate 
and returns the exit status of the command as returned by wait4().

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