c中的“System”命令用bash管道给出错误的输出

I am trying to understand the internal working of pipes and C when I noticed if I run

当我注意到我跑的时候，我正试图理解管道和C的内部工作

int main() { 
    system("ls | grep d | wc");                        
}

Output:

输出：

3       3      53

But on running the same command with bash I get

但是在用bash运行相同的命令时我得到了

3       3      104

Output of ls | grep d

输出ls | grep d

question_1.pdf question_2.pdf question_2_dataset.txt

Can someone explain the cause of this discrepancy? The same thing occurs if I use pipe via pipe() call in C.

有人可以解释这种差异的原因吗？如果我在C中使用管道通过管道（）调用，会发生同样的事情。

3 个解决方案

#1

Actually I figured out problem wasn't with ls but "grep --color=always d" which is alias of grep in my bash. The colored characters have extra length which increase the length of output.

实际上我发现问题不是ls而是“grep --color = always d”，这是我的bash中的grep的别名。彩色字符有额外的长度，增加了输出的长度。

#2

Check out what your 'ls' command at the bash is! Try:

看看你在bash上的'ls'命令是什么！尝试：

type ls

类型ls

You probably will find that ls is an alias of some kind.

您可能会发现ls是某种别名。

Check your bash-test again with

再次检查你的bash-test

/bin/ls | grep d | wc

/ bin / ls | grep d |厕所

If you then get th esame result as in your C-Code you will know what went wrong.

如果您在C代码中获得了esame结果，您就会知道出了什么问题。

#3

ls is often an alias in an interactive shell. For example, in my bash session if I do type ls I get

ls通常是交互式shell中的别名。例如，在我的bash会话中，如果我输入ls，我得到

ls is aliased to `ls -t --group-directories-first  -I .pyc -I __pycache__ -I .git  --color=auto -xF'

(The alias usually comes from $HOME/.bashrc or /etc/bash.bashrc).

（别名通常来自$ HOME / .bashrc或/etc/bash.bashrc）。

Now if you do:

现在，如果你这样做：

sh -c 'ls | grep d | wc'

(or command ls| command grep d | command wc ) you should get absolutely the same result as with compiling

（或命令ls |命令grep d |命令wc）你应该得到与编译完全相同的结果

int main() { system("ls | grep d | wc"); }

and running it in the same directory.

并在同一目录中运行它。

#1