added microshell

Exam_Rank_04/microshell.c

@@ -0,0 +1,185 @@
+#include "microshell.h"
+
+int	write_error(char *string, char *argv)
+{
+	while (string && *string)
+		write(2, string++, 1);
+	if (argv)
+		while(*argv)
+			write(2, argv++, 1);
+	write(2, "\n", 1);
+	return (1);
+}
+
+
+/**
+ * Used to execute a command passed to it
+-> The function denotes like cooking a dish in the kitchen. And:
+  av -> list of ingredients -> i -> current ingredient
+  tmp_fd -> cutting board  to prepare the ingredient
+  dup2 (tmp_fd, STDIN_FILENO) -> is moving the ingredient to the stove or oven
+  close -> keep the board away
+  execve -> actual cooking process. Takes the instruction(cmd) and prepares the ingredient(the argument)
+  and kitchen tools(envp) to execute.
+  If an error -> oven not working -> calls the write_error function to print
+
+*/
+int	ft_exe(char **argv, int i, int temporary_file_descriptor, char **environment_variables)
+{
+	argv[i] = NULL;
+	dup2(temporary_file_descriptor, STDIN_FILENO);
+	close(temporary_file_descriptor);
+	execve(argv[0], argv, environment_variables);
+	return (write_error("error: cannot execute ", argv[0]));
+}
+
+/**
+ *Imagine running a restaurant and having a list of customer orders to fullfil. 
+  Each order consists of series of dishes to prepare and serve. In order to comple
+  each order follow specific workflow <_>
+
+  1. Setup the kitchen with necessary utensils, ingredients and equipment ->initial setup
+   of shell environment and file descriptor.
+  2. Break the dishes into smaller sub-tasks to be executed sequentially. Breaking down of 
+   cmd arguments and separating them into individual cmd to be executed one by one.
+  3. For every cmd -> the type of tasks needs to be determined.
+     -> includes : preparing a specific dish  / cleaning set of utensils -> (for ex: builtin "cd" 
+	 or system command to be executed.
+  4. If cmd builtin -> execute directly and move to the next like serving glass of water and
+     move on to the next item in the order.
+  5. If cmd is system cmd -> we have to determine if executed alone or part of pipeline
+   IF alone executed -> fork the child process and execute command in child process 
+
+  6. Otherwise -> create new pipe and fork a child to execute first cmd in pipeline ->then
+    pass output of that cmd to the next cmd in the pipeline. 
+	Its like preparing a dish requiring multiple steps, like cooking a pasta dish requiring 
+	boiling water and preparing the sauce separately.
+  7. Once all executed -> clean up the kitchen and prepare the next order.
+    _> closing of the fd and freeing allocated memory.
+*/
+
+
+int	main(int argc, char **argv, char **environment_variables)
+{
+	int	i;
+	int fd[2];
+	int temporary_file_descriptor;
+	(void)argc;
+
+	i = 0;
+	temporary_file_descriptor = dup(STDIN_FILENO);
+	while (argv[i] && argv[i + 1])
+	{
+		argv = &argv[i + 1];
+		i = 0;
+		while (argv[i] && strcmp(argv[i], ";") && strcmp(argv[i], "|"))
+			i++;
+		if (strcmp(argv[0], "cd") == 0) //cd
+		{
+			if (i != 2)
+				write_error("error: cd: bad arguments", NULL);
+			else if (chdir(argv[1]) != 0)
+				write_error("error: cd: cannot change directory to ", argv[1]	);
+		}
+		else if (i != 0 && (argv[i] == NULL || strcmp(argv[i], ";") == 0))
+		{
+			if ( fork() == 0)
+			{
+				if (ft_exe(argv, i, temporary_file_descriptor, environment_variables))
+					return (1);
+			}
+			else
+			{
+				close(temporary_file_descriptor);
+				while(waitpid(-1, NULL, WUNTRACED) != -1)
+					;
+				temporary_file_descriptor = dup(STDIN_FILENO);
+			}
+		}
+		else if(i != 0 && strcmp(argv[i], "|") == 0)
+		{
+			pipe(fd);
+			if ( fork() == 0)
+			{
+				dup2(fd[1], STDOUT_FILENO);
+				close(fd[0]);
+				close(fd[1]);
+				if (ft_exe(argv, i, temporary_file_descriptor, environment_variables))
+					return (1);
+			}
+			else
+			{
+				close(fd[1]);
+				close(temporary_file_descriptor);
+				temporary_file_descriptor = fd[0];
+			}
+		}
+	}
+	close(temporary_file_descriptor);
+	return (0);
+}
+
+
+
+// int main(int ac,char **av,char **envp)
+// {
+// 	int i;
+// 	int fd[2];
+// 	int tmp_fd;
+// 	(void)ac;
+
+// 	i = 0;
+// 	tmp_fd = dup(STDIN_FILENO);
+// 	while(av[i] && av[i + 1])
+// 	{
+// 		av = &av[i + 1];
+// 		i = 0;
+// 		while (av[i] && strcmp(av[i], ';') && strcmp(av[i], '|') == 0)
+// 			i++;
+// 		if (strcmp(av[0], "cd") == 0)
+// 		{
+// 			if (i != 2)
+// 				write_error("error:cd bad arguments", NULL);
+// 			else if (chdir(av[1] != 0))
+// 				write_error("error: cd: cannot change directory to", av[1]);
+// 		}
+// 		else if (i != 0 && (av[i] == NULL || strcmp(av[i], ';') == 0))
+// 		{
+// 			if (fork() == 0)
+// 			{
+// 				if (ft_exe(av, i, tmp_fd, envp))
+// 					return (1);
+// 			}
+// 			else
+// 			{
+// 				close(tmp_fd);
+// 				while(waitpid(-1, NULL, WUNTRACED) != -1)
+// 					;
+// 				tmp_fd = dup(STDIN_FILENO);
+// 			}
+// 		}
+// 		else if (i != 0 && strcmp(av[i], "|") == 0)
+// 		{
+// 			pipe(fd);
+// 			if (fork() == 0)
+// 			{
+// 				dup2(fd[1], STDOUT_FILENO);
+// 				close(fd[0]);
+// 				close(fd[1]);
+// 				if (ft_exe(av, i, tmp_fd, envp));
+// 					return (1);
+// 			}
+// 			else
+// 			{
+// 				close(fd[1]);
+// 				close(tmp_fd);
+// 				tmp_fd = fd[0];
+// 			}
+// 		}
+// 	}
+// 	close(tmp_fd);
+// 	return (0);
+// }
+
+
+

Exam_Rank_04/microshell.h

@@ -0,0 +1,11 @@
+#ifndef MICROSHELL_H
+# define MICROSHELL_H
+
+#include <string.h> // strcmp
+#include <unistd.h> // write, dup, dup2, close, execve, chdir and fork
+#include <sys/wait.h> // waitpid
+
+int write_error(char *string, char *argv);
+int	ft_exe(char **argv, int i, int temporary_file_descriptor, char **environment_variables);
+
+#endif