shell.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

#define TOK_DELIM " \t\r\n"
#define RED "\033[0;31m"
#define RESET "\e[0m"
#define TK_BUFF_SIZE 1024

char *read_line();
char **split_line(char *);
int dash_exit(char **);
int dash_execute(char **);

int dash_execute(char **args){
    pid_t cpid;
    int status;

    if(strcmp(args[0],"exit")==0){
        return dash_exit(args);
    }

    cpid=fork();
    if(cpid==0){
        if(execvp(args[0],args)<0)
        printf("dash: command not found: %s\n",args[0]);
        exit(EXIT_FAILURE);
    }else if(cpid<0){
        printf(RED"Error forking"RESET"\n");
    }else{
        waitpid(cpid,&status,WUNTRACED);
    }
    return 1;
}

int dash_exit(char **args){
    return 0;
}

char **split_line(char *line){
    int buffsize=TK_BUFF_SIZE,position=0;
    char **tokens=(char **)malloc(sizeof(char*)*buffsize);
    char *token;

    if(!tokens){
        fprintf(stderr,"%sdash: Allocation error%s\n",RED,RESET);
        exit(EXIT_FAILURE);
    }
    token=strtok(line,TOK_DELIM);
    while(token!=NULL){
        tokens[position]=token;
        position++;

        if(position>=buffsize){
            buffsize+=TK_BUFF_SIZE;
            tokens=realloc(tokens,buffsize*sizeof(char*));

            if(!tokens){
                fprintf(stderr,"%sdash: Allocation error%s\n",RED,RESET);
                exit(EXIT_FAILURE);
            }
        }
        token=strtok(NULL,TOK_DELIM);
    }
    tokens[position]=NULL;

    return tokens;
}

char *read_line(){
    int buffsize=1024;
    int position=0;
    char *buffer=(char*)malloc(sizeof(char)*buffsize);
    int c;

    if(!buffer){
        fprintf(stderr,"%sdash: Allocation error%s\n",RED,RESET);
        exit(EXIT_FAILURE);
    }

    while(1){
        c=getchar();
        if(c==EOF || c=='\n'){
            buffer[position]='\0';
            return buffer;
        } else {
            buffer[position]=c;
        } 
        position++;

        if(position>=buffsize){
            buffsize+=1024;
            buffer=realloc(buffer,buffsize*sizeof(char));

            if(!buffer){
                fprintf(stderr,"%sdash: Allocation error%s\n",RED,RESET);
                exit(EXIT_FAILURE);
            }
        }
    }
}

void loop(){
    char *line;
    char **args;
    int status=1;
    
    do{
        printf("> ");
        line=read_line();
        args=split_line(line);
        status=dash_execute(args);
        free(line);
        free(args);
    }  while(status);
}
int main(){
    loop();
    return 0;
}