System call EXECVE ()

EXECVE () System call Learning

First, a small program, its function is to print the parent-child process number, all parameters passed in and two environment variables (if any):

Process.c

#include <stdio.h>#include<sys/types.h>#include<unistd.h>#include<stdlib.h>intMainintargcChar*argv[],Char*env[]) {    inti;
Char *p; printf ("\n=========i am a process image!============\n"); printf ("\nmy pid =%d, Parentpid =%d\n", Getpid (), Getppid ());  for(i=0; i< argc; i++) printf ("\nargv[%d]:%s\n", I, argv[i]); P= Getenv ("ENV1"); if(P! =NULL) printf ("\nenv1 =%s\n", p); P= Getenv ("env2"); if(P! =NULL) printf ("\nenv2 =%s\n\n", p); printf ("\n============= Process =================\n\n"); Sleep (atoi (argv[1])); return  About;}

Another piece of code MYEXEC.C is as follows:

#include <stdio.h>#include<errno.h>#include<stdlib.h>#include<unistd.h>#include<sys/types.h>#include<fcntl.h>#defineERROR (flag)if(flag) {printf ("%d:", __line__);                Fflush (stdout); Perror ("Error");            Exit (errno); }intMain () {intRET =0; Char*argv[] = {" One"," A", NULL}; Char*env[] = {"env1=1111111111111","env2=2222222222222", NULL}; printf ("\nthis is myexec file, PID was%d, Ppid is%d\n", Getpid (), Getppid ()); //ret = execl ("process", "one", "a", NULL);//ret = EXECLP ("process", "one", "a", NULL);//ret = execle ("process", "one", "a", null,null);//ret = EXECV ("process", argv);//ret = EXECVP ("process", argv);ret= Execve ("Process", argv,env); ERROR (ret== -1); return 0;}

After "Make process myexec" is executed, the process and myexec two executables are generated under the current directory. The results of the implementation are as follows:

The PORCESS.C code prints out the incoming parameters and the environment variable number of the EXECVE () system call when the MYEXEC.C code executes.

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Transform the MYEXEC.C into the following code:

#include <stdio.h>#include<sys/wait.h>#include<errno.h>#include<stdlib.h>#include<unistd.h>#include<sys/types.h>#include<fcntl.h>#defineERROR (flag)if(flag) {printf ("%d:", __line__);                Fflush (stdout); Perror ("Error");            Exit (errno); }intMainintargcChar*argv[],Char*env[])    {pid_t pid; PID=Fork (); //pid = Vfork ();ERROR (PID== -1); if(PID = =0) {printf ("\nchild process is running\n"); printf ("\nmy pid =%d, parent PID =%d\n", Getpid (), Getppid ()); Char*arglist[] = {"Sleep","3", NULL}; EXECVP ("./process", arglist); printf ("process never go to here!\n"); _exit (0); }    intStat;    pid_t Child_pid; Child_pid= Wait (&stat); printf ("Child Process has exited, PID =%d\n\n", Child_pid); if(wifexited (STAT)) printf ("Child exited with code%d\n\n", Wexitstatus (stat)); Elseprintf ("Child Exit abnormally\n\n"); return 0;}

After you perform the make myexec process, the results are as follows:

The subprocess executes the process through EXECVP (). The parent process obtains the return value of the child process number and its (normal) exit run time (via Wexitstayus ()) through Wait ().

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A way to run terminal commands through C code:

Mysystem,c

#include <stdio.h><stdlib.h><time.h><sys/stat.h>  <unistd.h><sys/types.h><errno.h>int main (intChar *argv[]) {    system ("ls--color=tty");     return 0 ;}

Runs after the link is compiled and performs the same effect as running the "LS--color=tty" command at the terminal.

System call EXECVE ()