how to use exec() without any parameter?

Question

I wanna run "ls" command by exec(), and my code is exec("/bin/ls", NULL) but I got an text shows "A NULL argv[0] was passed through an exec system call." If I add "all" as parameter it woks. exec("/bin/ls","all",NULL)

however, when I use exec("/bin/ps", NULL), it works properly. So could you help me to figure out whats wrong with my program?

BTW: I use execl()

#include <iostream>
#include <unistd.h>             //required for fork()
#include <sys/types.h>          //required for wait()
#include <sys/wait.h>           //required for wait()

using namespace std;

int main(){
        string cmd="";
        string cmdpath="/bin/";
        cout<<endl<<getcwd(NULL,0)<<" >> ";
        cin>>cmd;
        cout<<endl;
        string cmdCmdpath = cmdpath+cmd;
        const char* charcmd = cmdCmdpath.c_str();

        int x = fork();
        if(x!=0){
                cout<<"The command "<<cmd<<" is running"<<endl;
                wait(NULL);
                cout<<"Im parent!"<<endl;
        }else if (x==0){
                cout<<"Im child!"<<endl;
                execl(charcmd,NULL);
                cout<<"Child done"<<endl;
        }

}

Possible duplicate of [Why can the execve system call run "/bin/sh" without any argv arguments, but not "/bin/ls"?](http://stackoverflow.com/questions/36673765/why-can-the-execve-system-call-run-bin-sh-without-any-argv-arguments-but-not) — Ciro Santilli OurBigBook.com, Feb 17 '17 at 07:05

score 2 · Answer 1 · answered Sep 30 '15 at 01:08

Carefully read desctiption of execl:

The first argument, by convention, should point to the filename associated with the file being executed.

It means, that second the execl parameter should be path, referred to the same file as the first one. Usually, the first and second parameters are same:

execl(charcmd, charcmd, NULL);

how to use exec() without any parameter?

1 Answers1