From 3821f764a8d8c7a0c3817d6cd754da35cbf72dee Mon Sep 17 00:00:00 2001
From: hellisabove <robertnedela15@gmail.com>
Date: Mon, 10 Jan 2022 00:24:23 +0200
Subject: [PATCH] Initial Commit

---
 Makefile |  19 +++++
 shell.c  | 249 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 268 insertions(+)
 create mode 100644 Makefile
 create mode 100644 shell.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..38b3d28
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,19 @@
+OBJS	= shell.o
+SOURCE	= shell.c
+HEADER	= 
+OUT	= ss
+CC	 = gcc
+FLAGS	 = -g -c
+LFLAGS	 = -lreadline
+
+all: $(OBJS)
+	$(CC) -g $(OBJS) -o $(OUT) $(LFLAGS)
+
+shell.o: shell.c
+	$(CC) $(FLAGS) shell.c 
+
+install: all
+	cp ss /usr/local/bin
+
+clean:
+	rm -f $(OBJS) $(OUT)
diff --git a/shell.c b/shell.c
new file mode 100644
index 0000000..f2922eb
--- /dev/null
+++ b/shell.c
@@ -0,0 +1,249 @@
+// C Program to design a shell in Linux
+#include<stdio.h>
+#include<string.h>
+#include<stdlib.h>
+#include<unistd.h>
+#include<sys/types.h>
+#include<sys/wait.h>
+#include<readline/readline.h>
+#include<readline/history.h>
+
+#define MAXCOM 1000 // max number of letters to be supported
+#define MAXLIST 100 // max number of commands to be supported
+
+// Clearing the shell using escape sequences
+#define clear() printf("\033[H\033[J")
+
+// Function to take input
+int takeInput(char* str)
+{
+	char* buf;
+
+	buf = readline("\n$ ");
+	if (strlen(buf) != 0) {
+		add_history(buf);
+		strcpy(str, buf);
+		return 0;
+	} else {
+		return 1;
+	}
+}
+
+// Function where the system command is executed
+void execArgs(char** parsed)
+{
+	// Forking a child
+	pid_t pid = fork();
+
+	if (pid == -1) {
+		printf("\nFailed forking child..");
+		return;
+	} else if (pid == 0) {
+		if (execvp(parsed[0], parsed) < 0) {
+			printf("\nCould not execute command..");
+		}
+		exit(0);
+	} else {
+		// waiting for child to terminate
+		wait(NULL);
+		return;
+	}
+}
+
+// Function where the piped system commands is executed
+void execArgsPiped(char** parsed, char** parsedpipe)
+{
+	// 0 is read end, 1 is write end
+	int pipefd[2];
+	pid_t p1, p2;
+
+	if (pipe(pipefd) < 0) {
+		printf("\nPipe could not be initialized");
+		return;
+	}
+	p1 = fork();
+	if (p1 < 0) {
+		printf("\nCould not fork");
+		return;
+	}
+
+	if (p1 == 0) {
+		// Child 1 executing..
+		// It only needs to write at the write end
+		close(pipefd[0]);
+		dup2(pipefd[1], STDOUT_FILENO);
+		close(pipefd[1]);
+
+		if (execvp(parsed[0], parsed) < 0) {
+			printf("\nCould not execute command 1..");
+			exit(0);
+		}
+	} else {
+		// Parent executing
+		p2 = fork();
+
+		if (p2 < 0) {
+			printf("\nCould not fork");
+			return;
+		}
+
+		// Child 2 executing..
+		// It only needs to read at the read end
+		if (p2 == 0) {
+			close(pipefd[1]);
+			dup2(pipefd[0], STDIN_FILENO);
+			close(pipefd[0]);
+			if (execvp(parsedpipe[0], parsedpipe) < 0) {
+				printf("\nCould not execute command 2..");
+				exit(0);
+			}
+		} else {
+			// parent executing, waiting for two children
+			wait(NULL);
+			wait(NULL);
+		}
+	}
+}
+
+// Help command builtin
+void openHelp()
+{
+	puts("\n***WELCOME TO MY SHELL HELP***"
+		"\nCopyright @ Suprotik Dey"
+		"\n-Use the shell at your own risk..."
+		"\nList of Commands supported:"
+		"\n>cd"
+		"\n>ls"
+		"\n>exit"
+		"\n>all other general commands available in UNIX shell"
+		"\n>pipe handling"
+		"\n>improper space handling");
+
+	return;
+}
+
+// Function to execute builtin commands
+int ownCmdHandler(char** parsed)
+{
+	int NoOfOwnCmds = 4, i, switchOwnArg = 0;
+	char* ListOfOwnCmds[NoOfOwnCmds];
+	char* username;
+
+	ListOfOwnCmds[0] = "exit";
+	ListOfOwnCmds[1] = "cd";
+	ListOfOwnCmds[2] = "help";
+	ListOfOwnCmds[3] = "hello";
+
+	for (i = 0; i < NoOfOwnCmds; i++) {
+		if (strcmp(parsed[0], ListOfOwnCmds[i]) == 0) {
+			switchOwnArg = i + 1;
+			break;
+		}
+	}
+
+	switch (switchOwnArg) {
+	case 1:
+		exit(0);
+	case 2:
+		chdir(parsed[1]);
+		return 1;
+	case 3:
+		openHelp();
+		return 1;
+	case 4:
+		username = getenv("USER");
+		printf("\nHello %s.\nMind that this is "
+			"not a place to play around."
+			"\nUse help to know more..\n",
+			username);
+		return 1;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+// function for finding pipe
+int parsePipe(char* str, char** strpiped)
+{
+	int i;
+	for (i = 0; i < 2; i++) {
+		strpiped[i] = strsep(&str, "|");
+		if (strpiped[i] == NULL)
+			break;
+	}
+
+	if (strpiped[1] == NULL)
+		return 0; // returns zero if no pipe is found.
+	else {
+		return 1;
+	}
+}
+
+// function for parsing command words
+void parseSpace(char* str, char** parsed)
+{
+	int i;
+
+	for (i = 0; i < MAXLIST; i++) {
+		parsed[i] = strsep(&str, " ");
+
+		if (parsed[i] == NULL)
+			break;
+		if (strlen(parsed[i]) == 0)
+			i--;
+	}
+}
+
+int processString(char* str, char** parsed, char** parsedpipe)
+{
+
+	char* strpiped[2];
+	int piped = 0;
+
+	piped = parsePipe(str, strpiped);
+
+	if (piped) {
+		parseSpace(strpiped[0], parsed);
+		parseSpace(strpiped[1], parsedpipe);
+
+	} else {
+
+		parseSpace(str, parsed);
+	}
+
+	if (ownCmdHandler(parsed))
+		return 0;
+	else
+		return 1 + piped;
+}
+
+int main()
+{
+	char inputString[MAXCOM], *parsedArgs[MAXLIST];
+	char* parsedArgsPiped[MAXLIST];
+	int execFlag = 0;
+
+	while (1) {
+		// take input
+		if (takeInput(inputString))
+			continue;
+		// process
+		execFlag = processString(inputString,
+		parsedArgs, parsedArgsPiped);
+		// execflag returns zero if there is no command
+		// or it is a builtin command,
+		// 1 if it is a simple command
+		// 2 if it is including a pipe.
+
+		// execute
+		if (execFlag == 1)
+			execArgs(parsedArgs);
+
+		if (execFlag == 2)
+			execArgsPiped(parsedArgs, parsedArgsPiped);
+	}
+	return 0;
+}
+