OS: executing binaries is now supported.

os/extra/src/input.l

@@ -70,7 +70,7 @@ cd {
         return CD;
     }
 
-    /* Identifiers: source */
+    /* Identifiers: source, cat, echo */
 {id} {
         column_no += yyleng;
         yylval.str = strdup(yytext);
@@ -97,7 +97,7 @@ cd {
     }
 
     /* Argument (filenames and such): hello.txt, .config */
-{id}[^\t\n ]+ {
+{id}[^\t\n |]+ {
         column_no += yyleng;
         yylval.str = strdup(yytext);
         return ARGUMENT;

os/extra/src/input.l.h

@@ -61,6 +61,7 @@ void shell_help();
 void shell_pipe();
 void shell_repeat(int prev);
 void shell_exec(shell_args *args);
+void shell_exec_process(shell_args *args);
 
 /*
  * Doubly linked list containing all executed commands.

os/extra/src/main.c

@@ -12,6 +12,8 @@
 #include <unistd.h>
 #include <stdarg.h>
 #include <math.h>
+#include <signal.h>
+#include <sys/wait.h>
 
 #include "input.yacc.h"
 #include "input.lex.h"
@@ -133,18 +135,135 @@ shell_args *shell_pop_args() {
 
 void shell_exec(shell_args *args) {
     assert(args && args->arg);
-    shell_debug("exec %s", 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);
+        shell_debug("argument: `%s'", cur->arg);
         cur = cur->next;
     }
 
-    // Append to command history.
+    // Fork the process and handle forking error.
+    pid_t pid = fork();
+    switch( pid ) {
+        case -1:
+            shell_error("Error when forking");
+            exit(EXIT_FAILURE);
+        case 0:
+            shell_debug("Child process #%d is ready.", getpid());
+            shell_exec_process(args);
+        break;
+        default:
+            shell_debug("Parent launched child process #%d.", pid);
             shell_history_append(FN_EXEC, args);
+    }
+}
+
+/*
+ * Helper function for shell_exec(), which executes the process using execv()
+ * and handles all occurred errors caused by execv().
+ */
+void shell_exec_process(shell_args *args) {
+    assert(args && args->arg);
+
+    char *bin = malloc((5 + strlen(args->arg) + 1) * sizeof(char));
+    bin = strcpy(strcpy(bin, "/bin/")+5, args->arg)-5;
+
+    // Count the arguments.
+    int argc = 0;
+    for( shell_args *arg = args; arg; arg = arg->next, argc++);
+
+    // Convert argument structure to list of strings. And add a NULL pointer as
+    // a marker for the end of the list. The first string should point to the
+    // binary being executed.
+    char **argv = malloc((argc+1) * sizeof(char *));
+    argv[0] = bin;
+    shell_args *cur = args + sizeof(shell_args *);
+    for( int a = 0; a < argc && cur; cur = args->next, a++)
+        argv[a] = strdup(cur->arg);
+    argv[argc] = NULL;
+
+    // Function execvp() searches in PATH-environment, which is more flexible
+    // (user can set its own preferences), but the assignment states execv()
+    // should be used, because only binaries in /bin should be loaded.
+    shell_debug("execv(%s, [...]) called.\n", bin);
+    execv(bin, argv);
+
+    // If the execv() call returns, an error occurred and errno contains the
+    // error number corresponding with the error occurred.
+    switch( errno ) {
+        case E2BIG:
+            shell_error("The total number of bytes in the environment (envp)"
+                    " and argument list (argv) is too large.");
+        break;
+        case EACCES:
+            shell_error("Search permission is denied on a component of the"
+                    " path prefix of filename or the name of a script "
+                    " interpreter. The file or a script interpreter is not a"
+                    " regular file. Execute permission is denied for the file"
+                    " or a script or ELF interpreter. The file system is"
+                    " mounted noexec.");
+        break;
+        case EFAULT:
+            shell_error("Filename points outside accessible address space.");
+        break;
+        case EINVAL:
+            shell_error("An ELF executable had more than one PT_INTERP segment"
+                    " (i.e., tried to name more than one interpreter).");
+        break;
+        case EIO:
+            shell_error("An I/O error occurred.");
+        break;
+        case EISDIR:
+            shell_error("An ELF interpreter was a directory.");
+        break;
+        case ELIBBAD:
+            shell_error("An ELF interpreter was not in a recognized format.");
+        break;
+        case ELOOP:
+            shell_error("Too many symbolic links were encountered in resolving"
+                    " filename or the name of a script or ELF interpreter.");
+        break;
+        case EMFILE:
+            shell_error("The process has the maximum number of files open.");
+        break;
+        case ENAMETOOLONG:
+            shell_error("Filename is too long.");
+        break;
+        case ENFILE:
+            shell_error("The system limit on the total number of open files"
+                    " has been reached.");
+        break;
+        case ENOENT:
+            shell_error("The file filename or a script or ELF interpreter does"
+                    " not exist, or a shared library needed for file or"
+                    " interpreter cannot be found.");
+        break;
+        case ENOEXEC:
+            shell_error("An executable is not in a recognized format, is for"
+                    " the wrong architecture, or has some other format error"
+                    " that means it cannot be executed.");
+        break;
+        case ENOMEM:
+            shell_error("Insufficient kernel memory was available.");
+        break;
+        case ENOTDIR:
+            shell_error("A component of the path prefix of filename or a"
+                    " script or ELF interpreter is not a directory.");
+        break;
+        case EPERM:
+            shell_error("The file system is mounted nosuid, the user is"
+                    " not the superuser, and the file has the set-user-ID or"
+                    " set-group-ID bit set. The process is being traced, the"
+                    " user is not the superuser and the file has the "
+                    " set-user-ID or set-group-ID bit set.");
+        break;
+        case ETXTBSY:
+            shell_error("Executable was open for writing by one or more"
+                    " processes.");
+        break;
+    }
 }
 
 void shell_pipe() {
@@ -165,6 +284,12 @@ void shell_exit() {
 
 void shell_help() {
     // TODO: implement help text.
+    puts("Builtin commands / macros:");
+    puts(" cd PATH - Change current working directory to PATH.");
+    puts(" exit    - Exit this shell (also CTRL + D).");
+    puts(" help    - This help text.");
+    puts(" !!      - Repeat previous shell command.");
+    puts(" !N      - Repeat Nth previous shell command.");
 
     // Append to command history.
     shell_history_append(FN_HELP, NULL);
@@ -249,10 +374,13 @@ shell_cmd *shell_history_get(int prev) {
         assert(cur);
         assert(cur->cmd);
         assert(cur->cmd->args);
-        printf("skipping [%d]: %s\n", prev, cur->cmd->args->arg);
+        shell_debug("skipping [%d]: %s\n", prev, cur->cmd->args->arg);
         cur = cur->prev;
     }
 
+    if( cur )
+        shell_debug("found [%d]: %s\n", prev, cur->cmd->args->arg);
+
     return cur ? cur->cmd : NULL ;
 }
 
@@ -302,7 +430,56 @@ void shell_repeat(int prev) {
     shell_history_add(cmd);
 }
 
+/*
+ * Process number of the parent shell.
+ */
+pid_t parent_pid;
+
+/*
+ * Signal handler for SIGINT, SIGTERM and SIGCHLD.
+ */
+void signal_handler(int signum) {
+    char *sig = "TERM";
+    pid_t pid;
+
+    // TODO: implement signal handling
+
+    switch( signum ) {
+        case SIGINT:
+            sig = "INT";
+        case SIGTERM:
+            if( (pid = getpid()) == parent_pid )
+                printf("Parent process received SIG%s and will exit.\n", sig);
+            else
+                printf("Process #%d received SIG%s and will exit.\n", pid, sig);
+            exit(1);
+        case SIGCHLD:
+            puts("Parent process received SIGCHLD.");
+            pid = wait(NULL);
+            printf("Child with id %d exited.\n", pid);
+        break;
+        default:
+            puts("This handler does not understand this type of signal.");
+    }
+}
+
+/*
+ * Main function, initiates the program.
+ */
 int main(void) {
+    struct sigaction action = {.sa_handler = signal_handler};
+
+    parent_pid = getpid();
+
+    // Bind signal handlers
+    if( sigaction(SIGINT, &action, NULL)
+        || sigaction(SIGTERM, &action, NULL)
+        || sigaction(SIGCHLD, &action, NULL) )
+    {
+        perror("An error occured while binding the signal handlers.\n");
+        exit(1);
+    }
+
     // Detect if terminal is attached.
     struct stat stats;
     fstat(0, &stats);