Added shell history and implemented builtin commands.

os/extra/src/Makefile

-CC=gcc
+CC=clang # gcc
 RM=rm -Rfv
 
 LFLAGS= -lm
@@ -21,6 +21,7 @@ shell: input.yacc.o input.lex.o main.o
 test: shell
 	 echo -n 'exit' | ./shell
 	 echo -n 'cd ../' | ./shell
+	 echo -n 'help' | ./shell
 	 echo -n 'cat input.l' | ./shell
 	 echo -n 'cat input.l | grep "id"' | ./shell
 	 echo -n '!!' | ./shell
@@ -33,7 +34,7 @@ input.yacc.h: input.yacc.c
 
 input.lex.c: input.l
 	`which flex35 2>/dev/null || which flex 2>/dev/null` \
-		-C --header-file=input.lex.h -o $@ -d $<
+		--interactive --header-file=input.lex.h -o $@ -d $<
 
 input.lex.h: input.lex.c
 

os/extra/src/input.l

 /*
- * input.l
+ * Shell input lexer (flex format).
  *
- * Shell input lexer
+ * Sander van Veen (6167969) / Taddeus Kroes (6054129).
+ * <sandervv@gmail.com>      / <taddeuskroes@hotmail.com>
  */
 
 %{
@@ -13,18 +14,18 @@
 #include "input.l.h"
 #include "input.yacc.h"
 
+// Column / line counters (used in error reporting)
 int line_no = 1, column_no = 0;
 
 extern int current_line(void){ return line_no; }
 extern int current_column(void){ return column_no; }
-
 extern void reset_line(void){ line_no = 1; }
 extern void reset_column(void){ column_no = 0; }
 
 %}
 
-%option nounput
 %option noyywrap
+%option nounput
 
 %x id
 %x num
@@ -57,6 +58,12 @@ exit {
         return EXIT;
     }
 
+    /* Help shell builtin */
+help {
+        column_no += 4;
+        return HELP;
+    }
+
     /* Change directory builtin */
 cd {
         column_no += 2;
@@ -83,14 +90,14 @@ cd {
     }
 
     /* Path or path with filename: ./a/, ../, config/, /tmp/, /tmp/file  */
-[^ ]*\/[^ ]* {
+\.*{id}?\/[^\t\n ]* {
         column_no += yyleng;
         yylval.str = strdup(yytext);
         return PATH;
     }
 
     /* Argument (filenames and such): hello.txt, .config */
-[\/{id}][^ ]+ {
+{id}[^\t\n ]+ {
         column_no += yyleng;
         yylval.str = strdup(yytext);
         return ARGUMENT;
@@ -98,22 +105,18 @@ cd {
 
 #[^\n]+ { /* ignore comments */ }
 
-    /* End of file is a separator */
-\0 {
-        line_no++;
-        reset_column();
-        return EOS;
-    }
-
     /* White space */
 \n {
         line_no++;
         reset_column();
+        shell_entry();
         return EOL;
     }
 
     /* White space */
-{wsp} { column_no++; }
+{wsp} {
+        column_no++;
+    }
 
 . {
         column_no++;

os/extra/src/input.l.h

+/*
+ * Shell function declarations.
+ *
+ * Sander van Veen (6167969) / Taddeus Kroes (6054129).
+ * <sandervv@gmail.com>      / <taddeuskroes@hotmail.com>
+ */
+
+#include "input.yacc.h"
+
+/*
+ * Helper functions for line/column counter manipulation (which are used for the
+ * lexer's error reporting).
+ */
 extern int current_line(void);
 extern int current_column(void);
+extern void reset_line();
+extern void reset_column();
 
 extern int yyparse();
 
-extern void reset_line();
-extern void reset_column();
+/*
+ * Helper functions for shell output messages.
+ */
+void shell_debug(const char *msg, ...);
+void shell_error(const char *msg);
+void shell_entry();
+
+/*
+ * Singly linked list of arguments.
+ */
+typedef struct shell_args {
+    char *arg;
+    struct shell_args *next;
+} shell_args;
+
+/*
+ * A shell command contains a function identifier and an argument list (list
+ * could be empty).
+ */
+typedef enum {FN_CD, FN_HELP, FN_EXIT, FN_EXEC} shell_func;
+
+typedef struct shell_cmd {
+    shell_func func;
+    shell_args *args;
+} shell_cmd;
+
+/*
+ * Helper functions for creating / manipulating argument objects.
+ */
+void shell_push_args(const char *value);
+void shell_append_args(const char *value);
+shell_args *shell_pop_args();
+void shell_free_args(shell_args *args);
+
+/*
+ * Builtin shell commands.
+ */
+void shell_change_dir(const char *path);
+void shell_exit();
+void shell_help();
+void shell_pipe();
+void shell_repeat(int prev);
+void shell_exec(shell_args *args);
+
+/*
+ * Doubly linked list containing all executed commands.
+ */
+typedef struct shell_history_log {
+    shell_cmd *cmd;
+    struct shell_history_log *prev;
+    struct shell_history_log *next;
+} shell_history_log;
+
+/*
+ * Shell history manipulation functions.
+ */
+void shell_history_add(shell_cmd *cmd);
+shell_cmd *shell_history_get(int prev);
+void shell_history_clear();
+void shell_history_append(shell_func type, shell_args *args);
 
-void start_shell_entry();
-void start_shell_pipe();

os/extra/src/input.y

 %{
 /*
- * Shell input grammar (yacc/bison format)
+ * Shell input grammar (yacc/bison format).
+ *
+ * Sander van Veen (6167969) / Taddeus Kroes (6054129).
+ * <sandervv@gmail.com>      / <taddeuskroes@hotmail.com>
  */
 
+#define YYDEBUG 1
+#define YYERROR_VERBOSE 1
+
 #include <stdio.h>
 #include <string.h>
 
-// #include "input.func.h"
 #include "input.yacc.h"
 #include "input.lex.h"
 #include "input.l.h"
 
 void yyerror(const char *str) {
-    fflush(stdout);
-    fflush(stderr);
     fprintf(stderr, "error: parser reported \"%s\" (line %d, column %d)\n", str,
             current_line(), current_column());
 
@@ -23,9 +26,10 @@ void yyerror(const char *str) {
 %}
 
 %token COMMENT IDENTIFIER ARGUMENT STRING INTEGER
-%token EOL EOS CD EXIT PATH
+%token EOL EOS CD EXIT PATH HELP
 
-%type <str> PATH INTEGER
+%type <str> PATH INTEGER IDENTIFIER ARGUMENT STRING
+%type <str> Argument
 
 %union {
     char * str;
@@ -35,29 +39,31 @@ void yyerror(const char *str) {
 
 %%
 
-Start: /* empty */
-    | Commands
+Start: Commands
     ;
 
-Commands: Command  /*{ printf("cmd: %s\n", $1); }*/
-/*    | Command EOS*/
-    | Commands EOL { start_shell_entry(); } Command
-    | Commands '|' { start_shell_pipe(); } Command
+Commands: Command
+    | Commands EOL Command
+    | Commands '|' { shell_pipe(); } Command
     ;
 
-Command: Builtin
-    | IDENTIFIER
-    | IDENTIFIER Arguments
+Command: /* Empty */
+    | Builtin
+    | IDENTIFIER { shell_push_args($1); }
+                 { shell_exec(shell_pop_args()); }
+    | IDENTIFIER { shell_push_args($1); }
+      Arguments  { shell_exec(shell_pop_args()); }
     ;
 
-Builtin: EXIT       { puts("Exit shell"); }
-    | CD PATH       { printf("CD %s\n", $2); }
-    | '!' '!'       { puts("Repeat last"); }
-    | '!' INTEGER   { printf("Repeat %d\n", atoi($2)); }
+Builtin: EXIT     { shell_exit(); }
+    | HELP        { shell_help(); }
+    | CD Argument { shell_change_dir($2); }
+    | '!' '!'     { shell_repeat(1); }
+    | '!' INTEGER { shell_repeat(atoi($2)); }
     ;
 
- Arguments: Argument
-    | Arguments ' ' Argument
+Arguments: Argument      { shell_append_args($1); }
+    | Arguments Argument { shell_append_args($2); }
     ;
 
 Argument: STRING

os/extra/src/main.c

 /*
  * Shell implementation using flex/bison.
+ *
+ * Sander van Veen (6167969) / Taddeus Kroes (6054129).
+ * <sandervv@gmail.com>      / <taddeuskroes@hotmail.com>
  */
 
 #include <stdlib.h>
 #include <stdio.h>
 #include <assert.h>
 #include <sys/stat.h>
+#include <unistd.h>
+#include <stdarg.h>
+#include <math.h>
 
 #include "input.yacc.h"
 #include "input.lex.h"
 #include "input.l.h"
 
+#define PATH_LENGTH 1024
+
 int is_interactive = 0;
+int is_debug_mode = 1;
+
+/*
+ * Display a non-fatal error message in stderr.
+ */
+void shell_error(const char *msg) {
+    fprintf(stderr, "error: %s\n", msg);
+}
+
+/*
+ * Return the length of an unsigned integer.
+ */
+inline int base10len(unsigned int n) {
+    int len = 0;
+    /* n < 10^16 */
+    if (n >= 100000000) { n /= 100000000; len += 8; }
+    /* n < 100000000 = 10^8 */
+    if (n >= 10000) { n /= 10000; len += 4; }
+    /* n < 10000 */
+    if (n >= 100) { n /= 100; len += 2; }
+    /* n < 100 */
+    if (n >= 10)
+        return len + 2;
+    else
+        return len + 1;
+}
+
+
+/*
+ * Display a debug message, when running in debug mode, in stderr.
+ */
+void shell_debug(const char *msg, ...) {
+    if( !is_debug_mode )
+        return;
+
+    // Count all '%' chars in message
+    int var_count = 0;
+    int buf_size = strlen(msg) + 1;
+    char *var_types = malloc(buf_size * sizeof(char));
+    for( int c = 0; c < buf_size; c++ )
+        if( msg[c] == '%' ) {
+            assert(c+1 < buf_size);
+            var_types[var_count] = msg[c+1];
+            var_count++;
+        }
+
+    // Calculate message buffer size.
+    va_list ap;
+    va_start(ap, msg);
+    int v;
+    for( int i = 0; i < var_count; i++ ) {
+        switch( var_types[i] ) {
+            case 's': buf_size += strlen(va_arg(ap, char *)); break;
+            case 'd':
+                v = va_arg(ap, int);
+                if( v == 0 )
+                    buf_size++;
+                else if( v > 0 )
+                    buf_size += base10len((unsigned int) v);
+                else
+                    buf_size += base10len((unsigned int) (v*-1));
+            break;
+            default: perror("Unsupported variable type used in debug message.");
+        }
+    }
+    va_end(ap);
+
+    // Assemble the debug message.
+    va_start(ap, msg);
+    char *buf = malloc(buf_size * sizeof(char));
+    if( vsnprintf(buf, buf_size, msg, ap) >= buf_size )
+        shell_error("shell_debug() failed to assemble message.");
+    else
+        fprintf(stderr, "debug: %s\n", buf);
+
+    // Clean up used memory.
+    free(var_types);
+    free(buf);
+}
+
+shell_args *cmd_args = NULL;
+shell_args *last_arg = NULL;
+
+void shell_push_args(const char *value) {
+    assert(cmd_args == NULL && last_arg == NULL);
+
+    last_arg = malloc(sizeof(shell_args));
+    last_arg->arg = strdup(value);
+    last_arg->next = NULL;
+
+    cmd_args = last_arg;
+}
+
+void shell_append_args(const char *value) {
+    assert(cmd_args != NULL && last_arg != NULL);
+
+    shell_args *next_arg = malloc(sizeof(shell_args));
+    next_arg->arg = strdup(value);
+    next_arg->next = NULL;
+
+    last_arg->next = next_arg;
+    last_arg = next_arg;
+}
+
+shell_args *shell_pop_args() {
+    assert(cmd_args && last_arg != NULL);
+    shell_args *args = cmd_args;
+    cmd_args = last_arg = NULL;
+    return args;
+}
+
+void shell_exec(shell_args *args) {
+    assert(args && args->arg);
+    shell_debug("exec %s", args->arg);
+
+    // TODO: handle arguments.
+    shell_args *cur = args->next;
+    while(cur) {
+        assert(cur->arg);
+        shell_debug("argument: %s", cur->arg);
+        cur = cur->next;
+    }
+
+    // Append to command history.
+    shell_history_append(FN_EXEC, args);
+}
+
+void shell_pipe() {
+    shell_debug("start pipe");
+}
+
+/*
+ * Gracefully exit the shell.
+ */
+void shell_exit() {
+    shell_debug("Exiting shell");
+
+    // Append to command history.
+    shell_history_append(FN_EXIT, NULL);
 
-void start_shell_pipe() {
-    printf("start pipe");
+    exit(EXIT_SUCCESS);
 }
 
-void start_shell_entry() {
-    printf(">>> ");
+void shell_help() {
+    // TODO: implement help text.
+
+    // Append to command history.
+    shell_history_append(FN_HELP, NULL);
+}
+
+/*
+ * Change the current working directory of the shell. This function handles
+ * absolute and relative paths and will return 0 when the directory is
+ * successfully changed, or otherwise 1 in case of an error (e.g.  path does not
+ * exist).
+ */
+void shell_change_dir(const char *path) {
+    shell_debug("change directory: %s", path);
+    char *cur = malloc((PATH_LENGTH+1) * sizeof(char));
+    shell_debug("before: %s", getcwd(cur, PATH_LENGTH));
+
+    // Depending on the file system, other errors can be returned.
+    switch( chdir(path) ) {
+        case 0:
+            // No error, always a good sign :-).
+        break;
+        case EACCES:
+            shell_error("Search permissions denied for path.");
+        break;
+        case EFAULT:
+            shell_error("Path points outside your accessible address space.");
+        break;
+        case EIO:
+            shell_error("An I/O error occurred.");
+        break;
+        case ELOOP:
+            shell_error("Too many symbolic links while resolving path.");
+        break;
+        case ENAMETOOLONG:
+            shell_error("Path is too long.");
+        break;
+        case ENOENT:
+            shell_error("The file does not exist.");
+        break;
+        case ENOMEM:
+            shell_error("Insufficient kernel memory was available.");
+        break;
+        case ENOTDIR:
+            shell_error("Path is not a directory.");
+        break;
+        default:
+            shell_error("Unknown error ocurred while changing directory.");
+        break;
+    }
+
+    shell_debug("after:  %s", getcwd(cur, PATH_LENGTH));
+
+    // Append to command history.
+    shell_push_args(path);
+    shell_history_append(FN_EXEC, shell_pop_args());
+}
+
+/*
+ * Each new line will start a new shell entry ("$ "), which is an indicator to
+ * the user that he is able to enter another command. This function will not do
+ * anything when there is no terminal attached to the shell (but, for example, a
+ * pipe to prevent the printing of redundant characters).
+ */
+void shell_entry() {
+    if( !is_interactive )
+        return;
+    printf("$ ");
+    fflush(stdout);
+}
+
+shell_history_log *shell_history = NULL;
+int shell_history_count = 0;
+
+shell_cmd *shell_history_get(int prev) {
+    assert(prev >= 1);
+
+    if( prev >= shell_history_count )
+        return NULL;
+
+    shell_history_log *cur = shell_history;
+    while( cur && cur->prev && --prev ) {
+        assert(cur);
+        assert(cur->cmd);
+        assert(cur->cmd->args);
+        printf("skipping [%d]: %s\n", prev, cur->cmd->args->arg);
+        cur = cur->prev;
+    }
+
+    return cur ? cur->cmd : NULL ;
+}
+
+void shell_history_add(shell_cmd *cmd) {
+    assert(cmd);
+
+    if( !shell_history ) {
+        shell_history = malloc(sizeof(shell_history_log));
+        shell_history->cmd = cmd;
+        shell_history->prev = shell_history->next = NULL;
+        shell_history_count = 1;
+    }
+    else {
+        shell_history_log *history = malloc(sizeof(shell_history_log));
+        history->cmd = cmd;
+        history->next = NULL;
+        history->prev = shell_history;
+        shell_history->next = history;
+        shell_history = history;
+        shell_history_count++;
+    }
+}
+
+void shell_history_clear() {
+    // TODO: free shell command history.
+}
+
+void shell_history_append(shell_func type, shell_args *args) {
+    shell_cmd *cmd = malloc(sizeof(shell_cmd));
+    cmd->func = type;
+    cmd->args = args;
+    shell_history_add(cmd);
+}
+
+void shell_repeat(int prev) {
+    shell_debug("repeat %d", prev);
+
+    assert(prev > 0);
+
+    // TODO: implement repeat builtin.
+    shell_cmd *cmd;
+    if( !(cmd = shell_history_get(prev)) ) {
+        shell_error("Cannot repeat command before recorded history.");
+        return;
+    }
+
+    shell_history_add(cmd);
 }
 
 int main(void) {
-    // Detect if terminal is attached
+    // Detect if terminal is attached.
     struct stat stats;
     fstat(0, &stats);
 
     // Looks like a tty, so we're in interactive mode.
-    if (S_ISCHR(stats.st_mode)) {
+    if (S_ISCHR(stats.st_mode))
         is_interactive = 1;
-        start_shell_entry();
-    }
     else if (S_ISFIFO(stats.st_mode))
         // Looks like a pipe, so we're in non-interactive mode.
+        is_interactive = 0;
+    else
         is_interactive = 1;
-    else {
-        is_interactive = 1;
-        start_shell_entry();
-    }
 
-    // Disable yacc debug mode
-    yyset_debug(1);
+    // Create the first shell entry.
+    shell_entry();
+
+    // Disable yacc debug mode.
+    yyset_debug(0);
 
-    // Start the shell parser
+    // Start the shell parser.
     if( yyparse() ) {
         fprintf(stderr, "Error: Parsing failed\n");
         return EXIT_FAILURE;
     }
 
-    // EOF reached: clean up the mess
+    // EOF reached: clean up the mess.
+    shell_history_clear();
     yylex_destroy();
 
     if( yyin )