LinuxQuestions.org - how can i use execl to replce process

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how can i use execl to replace process

I want to use switch function to replace 3 process .I had
written code as shown below.

switch(i){

case 3: execl("./33","33",0); break;

case 2: execl("./22","22",0); break;

case 1: execl("./11","11",0);

}

When I tried to execute the above.only the first case written in the switch was successful.Can I use execl in this way.If it is not the case can anyone tell me how can I dothis.

Thanks in advance

Unix/Linux does not have a "spawn process" function (Windows does apparently). In unix, this is split into fork and exec. fork creates a new process identical to the current one, and exec replaces the current process with a new one, which is why your code isn't working. After the first exec, the code doesn't exist anymore. You will need to do a fork/exec, such as

Code:

switch(i){

    case 3: if (!fork()) execl("./11", "11", 0); break;

    case 2: if (!fork()) execl("./22", "22", 0); break;

    case 1: if (!fork()) execl("./11", "11", 0); break;

}

fork returns the pid of the new process to the parent, and 0 to the child, which is how you distinguish which is which. In both cases, the program continues with the statement/instruction after the fork.

You'll also want to catch or ignore SIGCHLD or you will get a bunch of zombie processes, 'signal(SIGCHLD, SIG_IGN)' will suffice if you're not interested in the exit status.

If you want to do this a lot, you'll probably want to write a wrapper funtion.

See the man pages for full details.

edit:
"fork creates a new process identical to the current one,"

I should have said, except for the pid of course...

problem with execl ()

I got the out put for the following code

Code:

switch(i){

    case 3: if (!fork()) execl("./11", "11", 0); break;

    case 2: if (!fork()) execl("./22", "22", 0); break;

    case 1: if (!fork()) execl("./11", "11", 0); break;

}

But when I tried to implement it in my program only case 3
got executed. My Program is working fine but I got problem with switch case

Code:

        m=strcasecmp(c.buff,"C");

        

        n=strcasecmp(c.buff,"CPP");

        

        o=strcasecmp(c.buff,"JAVA");

        

        if(m==0){i=1;printf("m=%d\ti=%d\n",m,i);}



        if(n==0){i=2;printf("n=%d\ti=%d\n",n,i);}



        if(o==0){i=3;printf("o=%d\ti=%d\n",o,i);}



        switch(i){



        case 1:  if (!fork())



        execl("./11", "11", 0); break;



        case 2:  if (!fork()) 



        execl("./22", "22", 0); break;



        case 3:  if (!fork())



        execl("./33", "33", 0); 



        }



    }

Can u tell me where I went wrong.

Where is the break statement after each case?

Example:

case 1: if (!fork()) {
execl("./11", "11", 0); exit(0);
}
break;
default: exit(0);

When the fork returns 0 for the child process, the child process will just continue to the next case and execute the next one.

Even if I place break in each switch cases.Only case 3 got executed.But
I want to execute the case based on the condition.How can I do this

Hi Thanks for answering.I found out where I went wrong.