I have an assignment from school to write a shell program in linux. the idea is to exercise fork() and execv() functions.. the shell program is supposed to be the master and every command that the user prints will run in a new process. we also need to try running the command in every path from the enviroment variable PATH.
for some reason, the execv function isn't working.. any idea what i'm doing wrong?
Code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
int main()
{
pid_t pid;
char *sh="Shell>";
int i,pathindex=0, ret;
char line[80]; // getting the user prompt
char *paths[20]={"NULL"}; // 20 values path array
char *currentpath, *path; // current path to execute in
char *arg[]={NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL} ;
//////////////////////////////////////////////////////////////////////////////
path=getenv("PATH");
currentpath=strtok(path,":");
while (currentpath!=NULL)
{
paths[pathindex]=currentpath; // filling the paths array
currentpath=strtok(NULL,":"); // from enviroment variable
pathindex++; // PATH.
}
system("/usr/bin/clear");
printf("\n\nShell Program (OS Course)\n");
printf("-------------------------\n\n");
while (1)
{
printf("%s",sh);
gets(line);
arg[0]=strtok(line," "); // getting command
if (strcmp(line,"leave")==0) exit(0);
for (i=1;i<10;i++) arg[i]=strtok(NULL," "); //getting command arguments
pathindex=0;
while (paths[pathindex]!=NULL)
{
if ((pid=fork())<0)
{
printf("Error: Couldn't fork\n");
exit(1);
}
if (pid==0)
{
printf("trying to run %s in %s\n",arg[0],paths[pathindex]);
ret=execv(paths[pathindex],arg);
if (ret==-1) exit(1);
}
else { wait(); pathindex++; }
}
}
return 0;
}
I tried compiling a simple test file just to see if execv works and it did..
it was something like:
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LEARN ABOUT X11R4
setsid
SETSID(1) User Commands SETSID(1)NAME
setsid - run a program in a new session
SYNOPSIS
setsid [options] program [arguments]
DESCRIPTION
setsid runs a program in a new session. The command calls fork(2) if already a process group leader. Otherwise, it executes a program in
the current process.
OPTIONS -c, --ctty
Set the controlling terminal to the current one.
-w, --wait
Wait for the execution of the program to end, and return the exit value of this program as the return value of setsid.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
SEE ALSO setsid(2)AUTHOR
Rick Sladkey <jrs@world.std.com>
AVAILABILITY
The setsid command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux July 2014 SETSID(1)