Want to run a program from a program

GoboFraggle · 04-21-2003, 03:01 PM

I'm writing a C/C++ shell program using KDev on a Mandrake 9.0 system. I want to be able to launch programs using fork() and execvp() or something similar, but I have had no success getting anything to work. Can any anyone help me out. Here's my program so far. All the extra #include statements go along with things I've tried. I plan to weed out the unneeded ones.
What I've written so far sets up a continuous loop and parses the command line. Any help will be appreciated.
Gobo Fraggle

#ifdef HAVE_CONFIG_H
#include <stdio.h>
#include <dirent.h>
#include <sys/types.h>
#include <config.h>
#endif
#include <iostream>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

using namespace std;

int main(int argc, char *argv[])
{
struct myShell_struct {
int argc;
char *name;
char *argv[];
char *command_line[];
}myShell;

myShell.argc = 0;

int i;
fputs("DASH:/ ",stdout);
gets(myShell.argv[0]);

//Initiate shell loop
while(strcmp(myShell.argv[0],"exit"))
{
i=0;
myShell.argc = 0;

//Parse command line
myShell.command_line[0] = strtok(myShell.argv[0]," ");
i=1;
while ( (myShell.command_line[i]=strtok(NULL, " ")) != NULL)
{
// Calculate myShell.argc = # of command line arguments -1
i++;
myShell.argc++;
}

fputs("DASH:/ ",stdout);
gets(myShell.argv[0]);
}

return 0;
}

Mara · 04-21-2003, 03:19 PM

I don't know what you'd like to do exactly, but it should be something like this:

Code:

pid_t child_pid;
child_pid=fork();
if(child_pid!=0) {
         /* parent process */
} else {
        execvp(program, arglist);
}

where arglist is char** (list of chars, can be created using

Code:

char* arglist[]= { "arg1", "arg2","arg3",NULL};

(NULL is needed at the end).

pythagras · 04-21-2003, 03:51 PM

BE CAREFUL!

Putting a fork in a loop is a recipe for disaster. Fork is like hitting the "New Window" button on a web browser - it creates a copy of the process with which you can execute other programs on top of. A loop that goes screwy with a fork inside can be pretty nasty.

wapcaplet · 04-21-2003, 08:30 PM

Quote:

Originally posted by pythagras
Putting a fork in a loop is a recipe for disaster. Fork is like hitting the "New Window" button on a web browser - it creates a copy of the process with which you can execute other programs on top of. A loop that goes screwy with a fork inside can be pretty nasty.

It's even worse than that, since the number of procs doubles each time. After about 20 loop iterations (which would take a fraction of a microsecond on modern processors) you'd have about a million copies of your program running!