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my_shell.c

+#include  <stdio.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define MAX_INPUT_SIZE 1024
+#define MAX_TOKEN_SIZE 64
+#define MAX_NUM_TOKENS 64
+int tokenNo = 0;
+int fc=0;
+int bg_pgrp=0,bg_count=0;
+
+void termHandler(){
+	
+}
+
+void intHandler()
+{  
+    if(fc)
+    { kill(fc,SIGKILL);
+	waitpid(fc,NULL,0);
+	fc=0;
+	printf("\n");
+	}
+	else { 
+	printf("\n$ ");}
+	fflush(stdout);
+	}
+
+/* Splits the string by space and returns the array of tokens
+*/
+char **tokenize(char *line)
+{
+  char **tokens = (char **)malloc(MAX_NUM_TOKENS * sizeof(char *));
+  char *token = (char *)malloc(MAX_TOKEN_SIZE * sizeof(char));
+  int i, tokenIndex = 0;
+  tokenNo = 0;
+  
+  for(i =0; i < strlen(line); i++){
+
+    char readChar = line[i];
+
+    if (readChar == ' ' || readChar == '\n' || readChar == '\t'){
+      token[tokenIndex] = '\0';
+      if (tokenIndex != 0){
+	tokens[tokenNo] = (char*)malloc(MAX_TOKEN_SIZE*sizeof(char));
+	strcpy(tokens[tokenNo++], token);
+	tokenIndex = 0; 
+      }
+    } else {
+      token[tokenIndex++] = readChar;
+    }
+  }
+ 
+  free(token);
+  tokens[tokenNo] = NULL ;
+  return tokens;
+}
+
+
+int main(int argc, char* argv[]) {
+	char  line[MAX_INPUT_SIZE];            
+	char  **tokens;              
+	int i, status;
+	//signal(SIGTERM,SIG_IGN);   
+	// signal(SIGINT,intHandler);
+	struct sigaction sa_INT={0};
+	sa_INT.sa_handler = &intHandler;
+	sa_INT.sa_flags = SA_RESTART;
+
+	sigaction(SIGINT,&sa_INT,NULL); 
+
+	while(1) {			
+		
+		int ret = waitpid(-1,&status,WNOHANG);
+        if(ret>0){
+           printf("Shell: Background process finished with pid : %d\n",ret); 
+	       bg_count--;
+	    }	
+		/* BEGIN: TAKING INPUT */
+		bzero(line, sizeof(line));
+		printf("$ ");
+		scanf("%[^\n]", line);
+		getchar();
+
+	
+        
+		
+		//printf("Command entered: %s (remove this debug output later)\n", line);
+		/* END: TAKING INPUT */
+        
+		line[strlen(line)] = '\n'; //terminate with new line
+		tokens = tokenize(line);
+   
+       //do whatever you want with the commands, here we just print them
+
+	   if(tokens[0]==NULL)
+	   { continue; }
+
+       if(line[0] == 'c' && line[1] == 'd' ) // support for cd command
+	   {
+        if(tokens[2]!=NULL)
+		{
+			printf("Incorrect Number of Arguments For CD Command\n");
+					// Freeing the allocated memory	
+	     	for(i=0;tokens[i]!=NULL;i++){
+			   free(tokens[i]);
+		        }
+		     free(tokens);
+			 continue;
+		}
+
+		if( chdir(tokens[1]) != 0 )
+		   printf("Shell: Incorrect command\n");
+		continue; }
+
+//exit Command
+char *exit = "exit";
+if(strcmp(tokens[0],exit)==0)
+{
+//signal(SIGTERM,termHandler);
+if(bg_count){
+//printf("Group To Exit :%d\n",bg_pgrp);
+killpg(bg_pgrp,SIGTERM);
+//printf("Still Here\n");
+int ret;
+	while((ret=waitpid(-1,NULL,0)) != -1)
+	printf("Shell: Background process finished with pid : %d\n",ret);
+}
+	printf("exit\n");
+
+// Freeing the allocated memory	
+for(i=0;tokens[i]!=NULL;i++){
+free(tokens[i]);
+}
+free(tokens);
+break; 
+//continue;
+}		
+
+
+
+
+
+// BG execution		
+       //printf("%s\n",tokens[tokenNo-1]);
+       if(*tokens[tokenNo-1] == '&') // BG execution support
+
+	   {    //printf("Adding support for background execution soon!!\n");
+	         fc = fork();
+
+	        if(fc<0) { printf("Unable to create a child process!!\n");}
+            else if(fc==0) //child process code
+	   {    //printf("BG Process\n");
+		  
+		  tokens[tokenNo-1]=NULL;
+			execvp(tokens[0],tokens);
+	        printf("Command execution failed!!\n");
+            _exit(1);
+	   }
+
+	   else { 
+		 //parent code
+	    if(!bg_count) { 
+			setpgid(fc,fc);
+		 	bg_pgrp = getpgid(fc); 
+			bg_count = 1; }
+		  else
+		  { setpgid(fc,bg_pgrp); bg_count++; }
+		  //printf("BG Group : %d\n ", getpgid(fc)); fflush(stdout);
+
+	    printf("[%d]\n",fc);
+		fc=0;
+          //int wc = wait(NULL);
+	   }
+ // Freeing the allocated memory	
+		for(i=0;tokens[i]!=NULL;i++){
+			free(tokens[i]);
+		}
+		free(tokens);
+
+
+		continue;
+	   }
+
+
+
+
+
+
+	   fc = fork();
+
+	   if(fc<0) { printf("Unable to create a child process!!\n");}
+       else if(fc==0) //child process code
+	   {
+		execvp(tokens[0],tokens);
+	    printf("Command execution failed!!\n");
+        _exit(1);
+	   }
+	   else {  //parent code
+	      
+          int wc = waitpid(fc,&status,0);
+		  fc=0;
+		  //printf("process exited with pid : %d\n",wc);
+	   }
+		// for(i=0;tokens[i]!=NULL;i++){
+		// 	printf("found token %s (remove this debug output later)\n", tokens[i]);
+		// }
+       
+		// Freeing the allocated memory	
+		for(i=0;tokens[i]!=NULL;i++){
+			free(tokens[i]);
+		}
+		free(tokens);
+
+	}
+	return 0;
+}