blocks|key|1198036|text|system()调用sh来处理您的命令行，因此您可以获得通配符扩展等。exec()和它的朋友用新的进程映像替换当前的进程映像。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1198037|使用system()，您的程序将继续运行，并且您将获得有关所调用的外部命令的一些状态。使用exec()，您的进程将被清除。|1198038|一般而言，我猜您可以将system()视为更高级别的接口。您可以使用fork()、exec()和wait()的某种组合来复制它的功能。|1198039|要回答您的最后一个问题，system()会创建子进程，而exec()系列不会。为此，您需要使用fork()。|1198040|entityMap^0|0|8|A|2|Z|6|0|2|8|19|6|0|B|8|Y|6|15|6|1C|6|0|C|8|S|6|1B|6|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|18|8|@$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|M|$]]

<code>system()</code> calls out to <code>sh</code> to handle your command line, so you can get wildcard expansion, etc. <code>exec()</code> and its friends replace the current process image with a new process image.

With <code>system()</code>, your program continues running and you get back some status about the external command you called. With <code>exec()</code>, your process is obliterated.

In general, I guess you could think of <code>system()</code> as a higher-level interface. You could duplicate its functionality yourself using some combination <code>fork()</code>, <code>exec()</code>, and <code>wait()</code>.

To answer your final question, <code>system()</code> causes a child process to be created, and the <code>exec()</code> family do not. You would need to use <code>fork()</code> for that.

blocks|key|1413274|text|exec函数成功时会替换当前运行的进程映像，不会创建子进程(除非您之前使用fork()自己创建了子进程)。system()函数派生一个子进程，并在提供的命令执行完毕或出现错误时返回。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1413275|entityMap^0|11|6|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

The exec function replace the currently running process image when successful, no child is created (unless you do that yourself previously with <code>fork()</code>). The system() function does fork a child process and returns when the command supplied is finished executing or an error occurs.

blocks|key|1198110|text|system()将在它产生的子进程中执行所提供的命令。exec()将用您指定的新可执行文件的调用替换当前进程。如果你想使用exec派生一个子进程，你必须提前fork()你的进程。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1198111|entityMap^0|0|8|R|6|1P|4|26|6|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

<code>system()</code> will execute the supplied command in a child process that it spawns. <code>exec()</code> will replace the current process with the invocation of the new executable that you specify. If you want to spawn a child process using <code>exec</code>, you'll have to <code>fork()</code> your process beforehand.

blocks|key|1198171|text|system()将调用您的系统默认命令shell，它将执行作为参数传递的命令字符串，该命令串本身可能会也可能不会创建进一步的进程，这取决于命令和系统。无论采用哪种方法，至少都会创建一个命令shell进程。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1198172|使用system()可以调用任何命令，而使用exec()只能调用可执行文件。shell脚本和批处理文件必须由命令Shell执行。|1198173|它们基本上是完全不同的，用于不同的目的。此外，exec()替换了调用进程，并且不会返回。更有用的比较是system()和spawn()之间的比较。虽然system可能更易于调用，但它会返回一个值，告诉您是否调用了命令shell，并且不会告诉您命令本身是否成功。使用spawn()可以获得进程的退出代码；按照惯例，非零值用于指示错误条件。与exec()类似，spawn()必须调用可执行文件，而不是shell脚本或内置命令。|1198174|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

system() will invoke your systems default command shell, which will execute the command string passed as an argument, that itself may or may not create further processes, that would depend on the command and the system. Either way, at least a command shell process will be created.

With system() you can invoke any command, whereas with exec(), you can only invoke an executable file. Shell scripts and batch files must be executed by the command shell.

Basically they are entirely different used for different purposes. Moreover exec() replaces the calling process, and does not return. A more useful comparison would be between system() and spawn(). While system may be simpler to invoke, it returns a value that tells you whether the command shell was invoked, and tells you nothing about the success of the command itself. With spawn() you can get the process's exit code; by convention non-zero is used to indicate error conditions. Like exec() spawn() must invoke an executable, not a shell script or built-in command.

blocks|key|1198231|text|exec()将当前正在运行的进程替换为performed..only函数的进程映像，可以使用此方法调用可执行文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1198232|system()隐式地派生出一个新进程来为请求提供服务，并返回通过它派生的子进程获得的值。initially.It使用系统的默认shell来执行操作。|1198233|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

exec() replaces the current running process with the process image of the function being performed..only executable files can be invoked using this.

system() forks off a new process implicitly to service the request and returns the value it obtained through the child process it forked initially.It uses the system's default shell to carry out the operation.

blocks|key|1198548|text|应该记住，exec(2)和system(3)之间有一些重要的区别。system()返回给调用者，而exec()用新图像替换现有代码。这已经在上面解释过了。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1198549|然而，当您想要运行一个过程，然后返回到您现有的代码，从被调用的过程接收返回代码时，就会出现不那么细微的区别。system()确实提供了返回码，但返回码只能用于检测错误情况，不能用于恢复返回码。|1198550|系统调用的一种可能的正确顺序是：|1198551|#include+<unistd.h>
#include+<sys/wait.h>
#define+NUMARGS+2

int+main+(int+argc,+char+*argv[])
{
++pid_t+child_pid,+wait_pid;
++int+*+child_status;
++char+*+exec_path+=+"/path/to/executable";
++char+*+child_args[NUMARGS]+=+{0,0};

++child_pid+=+fork();
++if+(0+==+child_pid)
++{+//+In+child+process
+++++...
+++++int+child_ret_code+=+execv(exec_path,+child_args);++//or+whichever+flavor+of+exec()+that+floats+your+boat
+++++...+//+if+child_ret_code+=+-1,+process+execv()+error+return
++}
++else+if+(-1+==+child_pid)
++{
+++++...+//process+error+return+from+fork
++}
++else+if+(0+<+child_pid)
++{++//+Parent+process
+++++wait_pid+=+wait(child_status);
+++++if+(-1+==+wait_pid)
+++++{
+++++++...+//Process+error+return+from+wait()
+++++}
+++++else
+++++{++//++Good+fork/exec/wait
++++++++if+(WIFEXITED(child_status))++//+Child+exited+normally+and+hopefully+returned+exit+code
++++++++{
+++++++++++int+child_ret_code+=+WEXITSTATUS(child_status);
+++++++++++...++//+Continue+on+as+you+would+after+call+to+system(3)
++++++++++++++++//+++except+now+you+have+the+return+code+you+needed
++++++++}
+++++}
++}
}|code-block|syntax|javascript|1198552|此序列还有其他微妙之处，可以通过仔细阅读相关手册页来确定，但此代码在没有信号、多个子进程等的情况下可以很好地工作。此外，内联声明可能会限制变量的范围，但包括在内是为了允许将此代码用作有效的模板(您可以使用不同的编码风格:-)。|1198553|entityMap^0|5|7|D|9|X|8|1D|6|0|1I|8|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|15|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|16|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|R|$]]

There are some significant differences between <code>exec(2)</code> and <code>system(3)</code> that should be kept in mind. <code>system()</code> returns to the caller, whereas <code>exec()</code> replaces the existing code with the new image. This has been explained above.

However, the not so subtle difference comes when you want to run a procedure and then return to your existing code, receiving the return code from the invoked procedure. <code>system()</code> does provide a return code, but the return code can only be used to detect an error condition, and cannot be used to recover a return code.

One possible proper sequence of system calls is:

<pre><code>#include &lt;unistd.h&gt;
#include &lt;sys/wait.h&gt;
#define NUMARGS 2

int main (int argc, char *argv[])
{
 pid_t child_pid, wait_pid;
 int * child_status;
 char * exec_path = "/path/to/executable";
 char * child_args[NUMARGS] = {0,0};

 child_pid = fork();
 if (0 == child_pid)
 { // In child process
 ...
 int child_ret_code = execv(exec_path, child_args); //or whichever flavor of exec() that floats your boat
 ... // if child_ret_code = -1, process execv() error return
 }
 else if (-1 == child_pid)
 {
 ... //process error return from fork
 }
 else if (0 &lt; child_pid)
 { // Parent process
 wait_pid = wait(child_status);
 if (-1 == wait_pid)
 {
 ... //Process error return from wait()
 }
 else
 { // Good fork/exec/wait
 if (WIFEXITED(child_status)) // Child exited normally and hopefully returned exit code
 {
 int child_ret_code = WEXITSTATUS(child_status);
 ... // Continue on as you would after call to system(3)
 // except now you have the return code you needed
 }
 }
 }
}
</code></pre>

There are other subtleties to this sequence which can be determined by a careful reading of the relevant man pages, but this code will work fine in the absence of signals, multiple child processes, etc. Also, the inline declarations may limit the scope of the variables, but are included to allow this code to be used as a template that works (you may use a different coding style :-).

blocks|key|1198740|text|除了child_status必须是一个整数(不是指向整数的指针)并且必须通过引用传递给JonSpencer函数之外，等待的答案是可以接受的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1198741|因此，代码基本上是相同的，只是改变了这两个东西：|1198742|#include+<unistd.h>
#include+<sys/wait.h>
#define+NUMARGS+2

int+main+(int+argc,+char+*argv[])
{
++pid_t+child_pid,+wait_pid;
++int+child_status;
++char+*+exec_path+=+"/path/to/executable";
++char+*+child_args[NUMARGS]+=+{0,0};

++child_pid+=+fork();
++if+(0+==+child_pid)
++{+//+In+child+process
+++++...
+++++int+child_ret_code+=+execv(exec_path,+child_args);++//or+whichever+flavor+of+exec()+that+floats+your+boat
+++++...+//+if+child_ret_code+=+-1,+process+execv()+error+return
++}
++else+if+(-1+==+child_pid)
++{
+++++...+//process+error+return+from+fork
++}
++else+if+(0+<+child_pid)
++{++//+Parent+process
+++++wait_pid+=+wait(&child_status);
+++++if+(-1+==+wait_pid)
+++++{
+++++++...+//Process+error+return+from+wait()
+++++}
+++++else
+++++{++//++Good+fork/exec/wait
++++++++if+(WIFEXITED(child_status))++//+Child+exited+normally+and+hopefully+returned+exit+code
++++++++{
+++++++++++int+child_ret_code+=+WEXITSTATUS(child_status);
+++++++++++...++//+Continue+on+as+you+would+after+call+to+system(3)
++++++++++++++++//+++except+now+you+have+the+return+code+you+needed
++++++++}
+++++}
++}
}|code-block|syntax|javascript|1198743|(指出我还没有足够的名气来评论Jon的帖子，所以我编辑了它。一些人拒绝了让我回答问题而不是编辑它的版本，但我认为在这种情况下，编辑现有代码只纠正一个小错误比编写完整的复制/粘贴/修改答案要简单、实用和清晰得多。)无论如何，感谢JonSpencer的回答，它对我真的很有用！|1198744|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

JonSpencer answer is fine, except that child_status must be an int (no a pointer to int) and has to be passed to wait function by reference.

So, the code would be mainly the same, just changing those couple of things:

<pre><code>#include &lt;unistd.h&gt;
#include &lt;sys/wait.h&gt;
#define NUMARGS 2

int main (int argc, char *argv[])
{
 pid_t child_pid, wait_pid;
 int child_status;
 char * exec_path = "/path/to/executable";
 char * child_args[NUMARGS] = {0,0};

 child_pid = fork();
 if (0 == child_pid)
 { // In child process
 ...
 int child_ret_code = execv(exec_path, child_args); //or whichever flavor of exec() that floats your boat
 ... // if child_ret_code = -1, process execv() error return
 }
 else if (-1 == child_pid)
 {
 ... //process error return from fork
 }
 else if (0 &lt; child_pid)
 { // Parent process
 wait_pid = wait(&amp;child_status);
 if (-1 == wait_pid)
 {
 ... //Process error return from wait()
 }
 else
 { // Good fork/exec/wait
 if (WIFEXITED(child_status)) // Child exited normally and hopefully returned exit code
 {
 int child_ret_code = WEXITSTATUS(child_status);
 ... // Continue on as you would after call to system(3)
 // except now you have the return code you needed
 }
 }
 }
}
</code></pre>

(Point out that I don't have enough reputation yet to comment Jon's post so I edited it. Some people rejected the edition asking me to answer the question instead of editing it, but I think that in this case it is much simpler, practical and clear to edit an existing code just correcting a small mistake than to write a full copy/paste/modify answer.)
Anyway, thanks JonSpencer for your answer, it was really useful for me!

blocks|key|1413581|text|process.Given+()会创建子进程并调用另一个子shell，而exec()不会创建子进程，Example将清除差异。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1413582|一些代码。|1413583|exec('ls+-l')|1413584|echo+"1+2+3“//这将不会在bash中执行(因为exec命令使用相同的shell)|1413585|1413586|system+(ls+-l)+echo+"1+2+3“//这将在完成系统子进程后执行，因为它们与父PID不同。|1413587|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|P|8|@]|9|@]|A|$]]|$1|H|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|L|$]]

System() will create child process and invoke another sub shell while exec() will not create child process.Given Example will clear difference.

some code...

exec('ls -l')

echo "1 2 3" // This will not executed in bash (as exec command use same shell)

some code ...

system (ls -l)
echo "1 2 3" // This will be executed after finishing System child process as they are different from parent PID.

blocks|key|1198452|text|system()使用shell调用所需的程序或内置命令，这是一种低效的方式，因为shell是在程序启动之前启动的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1198453|对于exec系列系统调用，将创建一个全新的映像，也就是说，它们用路径或文件或您提到的任何参数指定的新进程替换当前进程。|1198454|要记住的是，当使用exec系列系统调用时，在启动新程序后，原始程序将不再运行。|1198455|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

system() invokes the desired program or built-in command using a shell, this is an inefficient way because a shell is started before the program is started. 

In the case of the exec family of system calls, a whole new image is being created, that is, they replace the current process with a new process specified by the path or file or whatever argument you are mentioning.

The thing to be kept in mind is that, when the exec family of system calls are used, the original program will no longer be running after the new one is started.

blocks|key|1413854|text|一般来说，"system“是非常低效的，除非你有很小的代码，否则你不应该使用它。如果你需要在你的进程中执行多个程序，你最好使用fork&exec，尽管这会使它变得更复杂。以下是它们之间的差异列表：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1413855|1-+"system“命令创建一个shell副本来执行您的程序。每次调用系统时，都会创建一个shell的副本。所以，当你有很多程序要在你的进程中执行时，不要使用它。|1413856|2-具体地说，如果您想执行"mv“、"mkdir”等系统函数，最好使用mkdir()、unlink()或remove()等例程，而不是通过“system+(”rm...“)或system("mkdir+...”)来执行它们。|1413857|3-由于系统调用shell来执行您所需的程序，因此您可能会遇到一些用户权限问题。例如，有人可能会破解您的代码并执行其他程序，而不是您打算通过系统命令执行的程序。|1413858|有关更多信息，您可以阅读本书的第11章:+David+Curry的"UNIX系统编程“。|1413859|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|O|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

In general, "system" is so inefficient and you should not use it unless you have a small code. If you need to execute several programs in your process, you would better use fork&amp;exec though you make it more complicated.
 Here is a list of differences between them:

1- "system" command creates a copy of shell to execute your program. Every time you call a system, you create a copy of shell. So do not use it when you have lots of programs to execute inside your process.

2- Specifically, if you want to execute system functions such as "mv", "mkdir", it would be better to use routines such as mkdir(), unlink() or remove() instead of executing them through "system("rm ....") or system("mkdir ....")".

3- Since system calls shell to execute your desired program, you may have some user permission problems. For example, someone may crack your code and execute something else instead of the program you intended to execute through system command.

For more information, you may read chapter 11 of this book:
"UNIX Systems Programming" by David Curry.

What is the difference between <code>system</code> and <code>exec</code> family commands? Especially I want to know which one of them creates child process to work?

Difference between "system" and "exec" in Linux?

system和exec系列命令有什么区别？我特别想知道他们中的哪一个创建子进程来工作？

问Linux中"system“和"exec”的区别？
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