Project: creating a shell

Author: dalmia

3-Process Concept/project - shell/aman_shell.c

@@ -0,0 +1,194 @@
+#include <sys/types.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+#define LSH_RL_BUFSIZE 1024 /* buffer size for reading user input */
+#define LSH_TOK_BUFSIZE 64
+#define LSH_TOK_DELIM " \t\r\n\a"
+
+/* Function declarations for built-in shell commands */
+int lsh_cd(char **args);
+int lsh_help(char **args);
+int lsh_exit(char **args);
+
+/* List of built-in commands, followed by their corresponding functions */
+char *builtin_str[] = {
+ "cd",
+ "help",
+ "exit"
+};
+
+int (*builtin_func[]) (char **) = {
+ &lsh_cd,
+ &lsh_help,
+ &lsh_exit
+};
+
+int lsh_num_builtins(){
+ return sizeof(builtin_str) / sizeof(char *);
+}
+
+/* Built-in function implementations */
+int lsh_cd(char **args)
+{
+ if(args[1] == NULL){
+ fprintf(stderr, "lsh: expected argument to \"cd\"\n");
+ }else{
+ if(chdir(args[1]) != 0){
+ perror("lsh");
+ }
+ }
+
+ return 1;
+}
+
+int lsh_help(char **args)
+{
+ int i;
+ printf("Aman Dalmia's LSH\n", );
+ printf("Type program names and arguments, and press enter\n");
+ printf("The following are built in:\n");
+
+ for(i = 0; i < lsh_num_builtins(); i++){
+ printf(" %s\n", builtin_str[i]);
+ }
+
+ printf("Use the man command for information on other programs.\n");
+ return 1;
+}
+
+int lsh_exit(char **args)
+{
+ return 0;
+}
+
+/* Launch a program */
+int lsh_launch(char **args){
+ pid_t pid, wpid;
+ int status;
+
+ pid = fork();
+ if(pid == 0){ /* child process */
+ if(execvp(args[0], args) == -1) perror("lsh");
+ exit(EXIT_FAILURE);
+ }else if(pid > 0){ /* parent process */
+ do{
+ wpid = waitpid(pid, &status, WUNTRACED);
+ }while(!WIFEXITED(status) && !WIFSIGNALED(status));
+ }else{ /* error forking */
+ perror("lsh");
+ }
+
+ return 1;
+}
+
+/* Execute the parsed arguments */
+int lsh_execute(char **args){
+ int i;
+
+ if(args[0] == NULL){ /* empty command was entered */
+ return 1;
+ }
+
+ for (i = 0; i < lsh_num_builtins(); i++){
+ if(strcmp(args[0], builtin_str[i]) == 0){
+ return (*builtin_func[i])(args);
+ }
+ }
+
+ return lsh_launch(args);
+}
+
+/* Parse input to get the arguments */
+char **lsh_split_line(char *line){
+ int bufsize = LSH_TOK_DELIM, position = 0;
+ char **tokens = malloc(bufsize * sizeof(char*));
+ char *token;
+
+ if(!tokens){
+ fprintf(stderr, "lsh: allocation error\n");
+ exit(EXIT_FAILURE);
+ }
+
+ token = strtok(line, LSH_TOK_DELIM);
+ while(token != NULL){
+ tokens[position] = token;
+ position++;
+
+ if(position >= bufsize){
+ bufsize += LSH_TOK_BUFSIZE;
+ tokens = realloc(tokens, bufsize * sizeof(char*));
+ if(!tokens){
+ fprintf(stderr, "lsh: allocation error\n");
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ token = strtok(NULL, LSH_TOK_DELIM);
+ }
+ tokens[position] = NULL;
+ return tokens;
+}
+
+/* Read input from stdin */
+char *lsh_read_line(void)
+{
+ int bufsize = LSH_RL_BUFSIZE;
+ int position = 0;
+ char *buffer = malloc(sizeof(char) * bufsize);
+ int c;
+
+ if(!buffer){
+ fprintf(stderr, "lsh: allocation error\n");
+ exit(EXIT_FAILURE);
+ }
+
+ while(1){
+ /* Read a character */
+ c = getchar()
+
+ if(c == EOF || c == '\n'){
+ buffer[position] = '\0';
+ return buffer;
+ }else{
+ buffer[position] = c;
+ }
+ position++;
+
+ /* If buffer exceeded, reallocate buffer */
+ if(position >= bufsize){
+ bufsize += LSH_RL_BUFSIZE;
+ buffer = realloc(buffer, bufsize);
+ if(!buffer){
+ fprintf(stderr, "lsh: allocation error\n");
+ exit(EXIT_FAILURE);
+ }
+ }
+ }
+}
+
+/* Loop for getting input and executing it */
+void lsh_loop(void)
+{
+ char *line;
+ char **args;
+ int status;
+
+ do {
+ printf(">");
+ line = lsh_read_line();
+ args = lsh_split_line();
+ status = lsh_execute(line);
+
+ free(line);
+ free(args);
+ } while(status);
+}
+
+int main(void)
+{
+ lsh_loop();
+
+ return EXIT_SUCCESS;
+}