/* fork.c - example of a fork in a program */

/* The program asks for UNIX commands to be typed and inputted to a string */

/* The string is then "parsed" by locating blanks etc. */

/* Each command and sorresponding arguments are put in a args array */

/* execvp is called to execute these commands in child process */

/* spawned by fork() */

/* cc -o fork fork.c */

#include <stdio.h>

#include <sys/types.h>

#include <unistd.h>

#include <pwd.h>

char *getusername() {

static struct passwd *ent;

static int cur_uid=-1;

if (getuid()==cur_uid) {

return ent->pw_name;

}

if (cur_uid==-1) cur_uid=getuid();

setpwent();

ent=getpwuid(cur_uid);

endpwent();

if (!ent) return "(null)";

return ent->pw_name;

}

char *getuserdir() {

static struct passwd *ent;

static int cur_uid=-1;

if (getuid()==cur_uid) {

return ent->pw_dir;

//return "~";

}

if (cur_uid==-1) cur_uid=getuid();

setpwent();

ent=getpwuid(cur_uid);

endpwent();

if (!ent) {

// fprintf (stdout, "whoo\n");

return "/"; // a std dir

}

return ent->pw_dir;

// return "~";

}

char *gethost() {

static char nome[100];

if (gethostname (nome, 12)) return "(null)";

return nome;

}

void init_banner() {

fprintf (stdout,"Tosco Shell v 0.00001 - _extended_\n\n");

}

void main () {

char buf[1024];

char *args[64];

char pwd[128];

init_banner();

for (;;)

{

/*

* Prompt for and read a command.

*/

// user@host[pwd] :

printf ("%s@%s[%s]: ", getusername() , gethost(), getcwd(pwd, sizeof(pwd)) );

if (gets (buf) == NULL)

{

printf ("\n");

exit (0);

}

/*

* Split the string into arguments.

*/

parse (buf, args);

/*

* Execute the command.

*/

execute (args);

}

}

/*

* parse--split the command in buf into

* individual arguments.

*/

parse (buf, args)

char *buf;

char **args;

{

while (*buf != (long) NULL)

{

/*

* Strip whitespace. Use nulls, so

* that the previous argument is terminated

* automatically.

*/

while ((*buf == ' ') || (*buf == '\t')) *buf++ = (long) NULL;

/*

* Save the argument.

*/

*args++ = buf;

/*

* Skip over the argument.

*/

while ((*buf != (long) NULL) && (*buf != ' ') && (*buf != '\t')) buf++;

}

*args = NULL;

}

/*

* execute--spawn a child process and execute

* the program.

*/

execute (args)

char **args;

{

int pid, status;

/*

* check exit.

*/

// fprintf (stdout,"Debug: %s - %s %s\n", *args, args[0], args[1]);

if ( *args==NULL ) return;

// echo

if ( strncmp (args[0], "echo" , 4) == 0) {

fprintf (stdout, "%s\n", args[1]);

return;

}

// exit

if ( strncmp (args[0], "exit" , 4) == 0) {

fprintf (stdout, "Quit. \n");

exit ();

}

// chdir

if ( strncmp (args[0], "cd", 2) == 0 ) {

if (!args[1]) args[1]=(char *) getuserdir();

chdir (args[1]);

return;

}

// setenv e getenv

if ( strncmp (args[0], "setenv", 6) == 0 ) {

if (strsep (args[1], "=") !=0 ) {

fprintf (stdout, "No = allowed punx\n");

return;

}

if ( strncmp (args[2], "=", 1)==0) {

fprintf (stdout, "Warning, the use of = is deprecated !\n");

fprintf (stdout, "%s=%s\n",args[1], args[3]);

setenv (args[1], args[3], 1);

return;

}

fprintf (stdout, "%s=%s\n",args[1], args[2]);

setenv (args[1], args[2], 1);

return;

}

if ( strncmp (args[0], "getenv", 6) == 0 ) {

fprintf (stdout, "%s=%s\n", args[1], getenv(args[1]));

return ;

}

/*

* Get a child process.

*/

if ((pid = fork ()) < 0)

{

perror ("fork");

exit (1);

/* NOTE: perror() produces a short error message on the standard

error describing the last error encountered during a call to

a system or library function.

*/

}

/*

* The child executes the code inside the if.

*/

if (pid == 0)

{

execvp (*args, args);

perror (*args);

exit (1);

/* NOTE: The execv() vnd execvp versions of execl() are useful when the

number of arguments is unknown in advance;

The arguments to execv() and execvp() are the name

of the file to be executed and a vector of strings contain-

ing the arguments. The last argument string must be fol-

lowed by a 0 pointer.

execlp() and execvp() are called with the same arguments as

execl() and execv(), but duplicate the shell's actions in

searching for an executable file in a list of directories.

The directory list is obtained from the environment.

*/

}

/*

* The parent executes the wait.

*/

while (wait (&status) != pid)

/* empty */ ;

}