如何在 C++/Linux 中执行外部命令？
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How can I execute external commands in C++/Linux?
提问by Lipis
I just want to know which is the best way to execute an external command in C++ and how can I grab the output if there is any?
我只想知道哪种是在 C++ 中执行外部命令的最佳方式，以及如何获取输出（如果有）？
Edit: I Guess I had to tell that I'm a newbie here in this world, so I think I'm gonna need a working example. For example I want to execute a command like:
编辑：我想我不得不说我是这个世界上的新手，所以我想我需要一个有效的例子。例如，我想执行如下命令：
ls -la
how do I do that?
我怎么做？
回答by Mehrdad Afshari
回答by Mehrdad Afshari
An example:
一个例子：
#include <stdio.h>
int main() {
FILE * f = popen( "ls -al", "r" );
if ( f == 0 ) {
fprintf( stderr, "Could not execute\n" );
return 1;
}
const int BUFSIZE = 1000;
char buf[ BUFSIZE ];
while( fgets( buf, BUFSIZE, f ) ) {
fprintf( stdout, "%s", buf );
}
pclose( f );
}
回答by Peter Kovacs
popendefinitely does the job that you're looking for, but it has a few drawbacks:
popen绝对可以完成您正在寻找的工作，但它有一些缺点：
- It invokes a shell on the command you're executing (which means that you need to untaint any user provided command strings)
- It only works in one direction, either you can provide input to the subprocess or you can read its output.
- 它在您正在执行的命令上调用一个 shell（这意味着您需要清除任何用户提供的命令字符串）
- 它只在一个方向上起作用，您可以向子流程提供输入，也可以读取其输出。
If you want invoke a subprocess and provide input and capture output then you'll have to do something like this:
如果要调用子流程并提供输入和捕获输出，则必须执行以下操作：
int Input[2], Output[2];
pipe( Input );
pipe( Output );
if( fork() )
{
// We're in the parent here.
// Close the reading end of the input pipe.
close( Input[ 0 ] );
// Close the writing end of the output pipe
close( Output[ 1 ] );
// Here we can interact with the subprocess. Write to the subprocesses stdin via Input[ 1 ], and read from the subprocesses stdout via Output[ 0 ].
...
}
else
{ // We're in the child here.
close( Input[ 1 ] );
dup2( Input[ 0 ], STDIN_FILENO );
close( Output[ 0 ] );
dup2( Output[ 1 ], STDOUT_FILENO );
execlp( "ls", "-la", NULL );
}
Of course, you can replace the execlpwith any of the other exec functions as appropriate.
当然，您可以根据需要将 替换为execlp任何其他 exec 函数。
