UNIX for Advanced & Expert Users

Hey guys,

I'm given this bit of code, but, I'm having some problems executing it with the functions I've defined so far. I'm suppose to define the funtions "parse" and "execute." Parse splits the command in buf into individual arguments. It strips whitespace, replacing those it finds with NULLS thereby defining where an argument ends.

How would I create the function execute using 'execvp' which creates a child process with the commands developed in the function parse?


The code is:
.................................................................................................... .....

#define MAX 512



void parse(char* buf, char** args);

void execute(char** args);



int main()

{

char buf[MAX];

char* args[64];



for ( ; ; )

{

/* prompt for a read a command */

printf(“Command: “);

if(fgets(buf, MAX,stdin) == ‘\0')

{

printf(“\n”);

exit(0);

}



/* Split the command string into arguments */

parse(buf, args);



/* Execute the command. */

execute(args);

}



return 0;

}
.................................................................................................... .....

Thankx in advance.....

Hey,

Having followed what you said, this is what I was able to create.
However, its not executing the commands thru the terminal. Please take a look at it and let me know what you think please.

****************************************************
#include <stdio.h>

main()
{
char buf[1024];
char *args[64];

for (; {
/*
* Prompt for and read a command.
*/
printf("Command: ");

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 != NULL) {
/*
* Strip whitespace
*/
while ((*buf == ' ') || (*buf == '\t'))
*buf++ = NULL;

/*
* Save the argument.
*/
*args++ = buf;

/*
* Skip over the argument.
*/
while ((*buf != NULL) && (*buf != ' ') && (*buf ! '\t'))
buf++;
}

*args = NULL;
}

/*
* execute--spawn a child process and execute
* the program.
*/
execute(args)
char **args;
{
int pid, status;

/*
* Get a child process.
*/
if ((pid = fork()) < 0) {
perror("fork");
exit(1);
}

/*
* The child executes the code inside the if.
*/
if (pid == 0) {
execvp(*args, args);
perror(*args);
exit(1);
}

/*
* The parent executes the wait.
*/
while (wait(&status) != pid)
/* empty */ ;
}
****************************************************

Thanks in advance

Thanks for the input. Actually, the code is more Kernighan & Ritchie as opposed to ANSI C as K&R is the book am using as my guide along with Unix Systems Programming SVR 4.

I'm yet to implement the further instructions you've given me as am not at a terminal just now. So, whenever I get that done, I'll let you know what I've formulated.

By the way, are you familiar with the Java environment? I have a question on graphics I want to ask you.

Hey,

check out this code... I tried running it with "fgets" as it states that "gets" is a dangerous code.... however, its not executing the linux commands... what could be the problem, or what in this code needs modification??


#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <wait.h>

#define MAX 1024

void parse(char*buf, char ** args);
void execute(char**args);

int main()
{
char buf[MAX];
char *args[64];

for(;{
/*Prompts for and reads a command*/
printf("Command: ");

if(fgets(buf, MAX, stdin) == '\0'){
printf("\n");
exit(0);
}

/*Splits the strings into arguments*/
parse(buf,args);

/*Executes the command*/
execute(args);
}
}

/* Parse: - Splits the commands in buf into individual arguments */
void parse(char*buf,char **args)
//char * buf;
//char ** args;
{
while(*buf != '\0'){

/*Strips the whitespace with the
use of null so previous argument
is terminated automatically*/

while(*buf == ' '|| *buf == '\t' || buf == '\n')
*buf++ = '\0';

/*Saves the argument*/

*args++ = buf;

/*Skips over the argument*/

while((*buf != '\0') && (buf != ' ') && (*buf != '\t') && (*buf != '\n'))
buf++;
}

*args = '\0';
}


/*Execute spawns the child process
and execute the program*/

void execute(char **args)
//char ** args;
{
pid_t pid;
int status;

/*Get a child process*/

if((pid = fork()) < 0){
perror("ERROR executing fork\n");
exit(1);
}

/*Child executes the code inside the if statement*/

if(pid == 0){
execvp(*args, args);
perror(*args);
exit(1);
}


/*The parent executes the wait*/


while (wait(&status) != pid)
/* empty */ ;

}


Thankx in advance.......