Implementing a command line interpreter in C, special case - c

Question

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#define BUFFER 64
char *read_command(void);
char **parse_line(char *line);
int execute(char **arguments);
int main(void)
{
char *command = NULL;
char **arguments;
int status;
do
{
printf("protoulis_7968> ");
command = read_command();
arguments = parse_line(command);
status = execute(arguments);
free(arguments);
free(command);
}while(status);
}
char *read_command(void)
{
char *command = NULL;
ssize_t buf = 0;
getline(&command, &buf, stdin);
return command;
}
char **parse_line(char *line)
{
int buffer = BUFFER;
int pos = 0;
char **tokens = malloc(buffer * sizeof(char*));
char *token;
if (!tokens)
{
printf("Error allocating memory with malloc\n");
exit(0);
}
token = strtok(line, " \t\r\n\a");
while(token != NULL)
{
tokens[pos] = token;
pos++;
if (pos >= buffer)
{
buffer += BUFFER;
tokens = realloc(tokens, buffer * sizeof(char*));
if (!tokens)
{
printf("Error reallocating memory!\n");
exit(0);
}
}
token = strtok(NULL, " \t\r\n\a");
}
tokens[pos] = NULL;
return tokens;
}
int execute(char **arguments)
{
// printf("%*c\n", arguments);
int pid, waitPid, status;
pid = fork();
if(pid == 0) //child process
{
if (execvp(arguments[0], arguments) == -1)
perror("Error with EXECVP\n");
}
else if (pid < 0)
perror("Error PID < 0\n");
else //parent process
{
do
{
waitPid = waitpid(pid, &status, WUNTRACED);
}while(!WIFEXITED(status) && !WIFSIGNALED(status));
}
return 1;
}
Well, I have written the above code simulating a command line interpreter in C. I would like to be able to execute multiple commands by entering them in one line. I mean I want to pass as input for example the line: ls -l ; touch hello.c ; pwd. Having passed this entire line I want to separate the commands by the semicolon and let the system execute each command in any order. I believe I have to use the strtok function but have done many attempts and managed nothing. Any help would be really appreciated!

Answer 1

strtok will not suffice in your case. The reason is that it will take you to the next subcommand but to be able to execute this subcommand, you have to have it as a single string.
Two ways to solve this issue:
Count how many ';' there is, replace them by '\0' to have several contiguous strings in memory, then execute them one by one.
Write a function that splits your command string into a 2d array of subcommands, then execute them one by one.
Here's a code that does that if you need some inspiration:
Using linked lists: https://github.com/yoones/chelpers/blob/master/src/split.c
2d array version: https://github.com/yoones/hsn/blob/master/src/tools/split.c