Shell-VII release

5 files changed, 483 insertions, 104 deletions

diff --git a/Makefile b/Makefile
index 9aa167e..691cedc 100644
--- a/Makefile
+++ b/Makefile
@@ -3,12 +3,12 @@ OBJMODULES = $(SRCMODULES:.c=.o)
 CC = gcc
 CFLAGS = -Wall -g -c
 
-all: shell-VI
+all: shell-VII
 
 %.o: %.с %.h
 	$(CC) $(CFLAGS) $< -o $@
 
-shell-VI: $(OBJMODULES)
+shell-VII: $(OBJMODULES)
 	$(CC) $(LIBS) $^ -o $@
 
 -include deps.mk
diff --git a/lexical_analysis.c b/lexical_analysis.c
index 5db57cb..eab4390 100644
--- a/lexical_analysis.c
+++ b/lexical_analysis.c
@@ -46,11 +46,39 @@ int is_empty_word(int ch, struct param_type params)
             params.empty_word_flag;
 }
 
-int command_execution_condition(struct param_type *params)
+static int find_end_subshell_before_cur_pos(struct readline_type *readline)
 {
+    int i;
+    for(i = readline->considered_index-1; i >= 0; --i) {
+        if(readline->arr[i] == ' ')
+            continue;
+        break;
+    }
+    return i >= 0 && readline->arr[i] == ')';
+}
+
+int command_execution_condition(struct param_type *params,
+                                struct readline_type *readline)
+{
+    if(params->tokens == and || params->tokens == or) {
+        if(find_end_subshell_before_cur_pos(readline))
+            return 0;
+    }
+    if(params->tokens == next_command) {
+        if(find_end_subshell_before_cur_pos(readline))
+            return 0;
+    }
+    if(params->tokens == '&') {
+        if(find_end_subshell_before_cur_pos(readline))
+            return 0;
+    }
+    if(params->tokens == '(' && params->pipeline)
+        return 1;
+
     return
         (params->tokens != '<' && params->tokens != '>' &&
-                params->tokens != append && !params->pipeline) ||
+        params->tokens != append && !params->pipeline &&
+        params->tokens != start_subshell) ||
         (params->pipeline && params->tokens == '&');
 }
 
@@ -59,24 +87,24 @@ int is_first_special_token_character(int ch)
     return ch == '<' || ch == '>' || ch == '&' || ch == '|' || ch == ';';
 }
 
-int excessive_words(int ch, struct param_type *params)
+int excessive_words(int ch, struct param_type *params,
+                    struct readline_type *readline)
 {
-    int next_ch;
-
     if(filename_waiting(params)) {
         if(ch == new_line)
             return 0;
-        while((next_ch = getchar()) != new_line) {
-            if(next_ch == ' ')
-                continue;
-            if(!is_first_special_token_character(next_ch)) {
+        int i;
+        for(i = readline->considered_index+1; i <= readline->last_element_index;
+                                                                        ++i)
+        {
+            if(readline->arr[i] == ' ')
+                    continue;
+            if(!is_first_special_token_character(readline->arr[i])) {
                 params->wrong_command = err_extra_chars_after_filename;
                 return 1;
-            }
-            else
+            } else
                 break;
         }
-        ungetc(next_ch, stdin);
     }
     return 0;
 }
@@ -101,16 +129,10 @@ int validate_redirections(int ch, int next_ch, struct param_type *params)
              params->streams.output_stream_to_append == NULL);
 }
 
-int is_double_token(struct param_type *params)
-{
-    return params->tokens == and || params->tokens == or ||
-            params->tokens == append;
-}
-
 int is_special_token(int ch, int next_ch)
 {
-    return (ch == '&' && next_ch == '&') || (ch == '|' && ch == '|') ||
-            ch == '&' || ch == ';' || ch == '|';
+    return (ch == '&' && next_ch == '&') || (ch == '|' && next_ch == '|') ||
+            ch == '&' || ch == ';' || ch == '|' || ch == '(' || ch == ')';
 }
 
 int is_redirect_token(int ch, int next_ch)
@@ -139,8 +161,8 @@ int stream_redirect_tokens(struct w_queue *word_chain,
 
         if(validate_redirections(ch, next_ch, params)) {
             params->tokens = (ch == '>' && next_ch == '>') ? append : ch;
-            if(is_double_token(params))
-                ++readline->considered_index;
+            if(params->tokens == append)
+                readline->considered_index += 2;
             return 1;
         } else
             params->wrong_command = err_redirect_stream_again;
@@ -167,12 +189,20 @@ int pipeline_token_processing(struct w_queue *word_chain,
                               struct dynamic_array *tmp_word,
                               struct param_type *params)
 {
+    /* pipeline after subshell */
+    if(tmp_word->last_element_index == -1 && params->tokens == start_subshell) {
+        params->tokens = '|';
+        params->pipeline = 1;
+        return 1;
+    }
+
     char **cmdline = NULL;
     if(is_stream_redirection_set(params) &&
             wrong_streams_redirection(params)) {
         params->wrong_command = err_redirect_stream_in_pipeline;
         return 0;
     }
+
     params->tokens = '|';
     params->pipeline = 1;
     cmdline =
@@ -184,44 +214,88 @@ int pipeline_token_processing(struct w_queue *word_chain,
     return 1;
 }
 
+static void stop_by_previous_effect_tokens(struct param_type *params)
+{
+    if((params->tokens == and && last_execution_status == 1) ||
+            (params->tokens == or && last_execution_status == 0))
+        params->wrong_command = err_set_failure;
+}
+
+static int find_repeated_background_symbol(struct readline_type *readline)
+{
+    int i;
+    for(i = readline->considered_index + 1; i <= readline->last_element_index;
+                                                                        ++i)
+    {
+        if(readline->arr[i] == '&')
+            return 1;
+    }
+    return 0;
+}
+
 /*
  * verification of special tokens (|, &, &&, ||), except redirection tokens
  */
 int special_tokens(struct w_queue *word_chain, struct c_queue *cmdlines,
-                   struct dynamic_array *tmp_word, int ch,
+                   struct dynamic_array *tmp_word, int *ch,
                    struct param_type *params, struct readline_type *readline)
 {
     int next_ch, i;
-
-    if(ch == '|' || ch == '&')
+    if(*ch == '|' || *ch == '&')
         next_ch = readline->arr[readline->considered_index + 1];
 
-    if(is_special_token(ch, next_ch)) {
+    if(is_special_token(*ch, next_ch)) {
         add_word_or_filename(word_chain, tmp_word, params);
+        stop_by_previous_effect_tokens(params);
 
         if(params->wrong_command)
             return 0;
 
-        if(ch == '|' && next_ch == '|')
+        if(*ch == '|' && next_ch == '|') {
             params->tokens = or;
-        else if(ch == '|') {
-            if(!pipeline_token_processing(word_chain, cmdlines, tmp_word,
-                                          params))
-                return 0;
-        } else if(ch == '&' && next_ch == '&')
+            readline->considered_index += 2;
+            return 1;
+        }
+        if(*ch == '|')
+            return pipeline_token_processing(word_chain, cmdlines, tmp_word,
+                                             params);
+        if(*ch == '&' && next_ch == '&') {
             params->tokens = and;
-        else if(ch == '&') {
+            readline->considered_index += 2;
+            return 1;
+        }
+        if(*ch == '&') {
+            /* repeated & */
+            if(find_repeated_background_symbol(readline)) {
+                params->wrong_command = err_repeated_background_ch;
+                return 0;
+            }
+
             for(i = readline->considered_index+1; readline->arr[i] != new_line;
                                                                         ++i) {
-                if(readline->arr[i] != whitespace && readline->arr[i] != tab) {
-                    params->wrong_command = err_bg_process;
-                    return 0;
-                }
+                if(readline->arr[i] == ' ')
+                    continue;
+                else
+                    break;
             }
+            if(readline->arr[i] == new_line)
+                *ch = new_line;
             params->tokens = '&';
+            return 1;
+        }
+        if(*ch == start_subshell) {
+            params->tokens = start_subshell;
+            return 1;
+        }
+        if(*ch == end_subshell) {
+            params->tokens = end_subshell;
+            return 1;
         }
-        if(is_double_token(params))
-            ++readline->considered_index;
+        if(*ch == next_command) {
+            params->tokens = next_command;
+            return 1;
+        }
+
         return 1;
     }
     return 0;
diff --git a/lexical_analysis.h b/lexical_analysis.h
index 9d7d556..7fc1734 100644
--- a/lexical_analysis.h
+++ b/lexical_analysis.h
@@ -12,18 +12,19 @@ int ignore_spaces(int ch, struct param_type params);
 int change_mode(int ch, struct param_type params);
 int start_escape_sequence(int ch, struct param_type params);
 int is_empty_word(int ch, struct param_type params);
-int command_execution_condition(struct param_type *params);
+int command_execution_condition(struct param_type *params,
+                                struct readline_type *readline);
 
 int is_special_token(int ch, int next_ch);
 int is_redirect_token(int ch, int next_ch);
-int excessive_words(int ch, struct param_type *params);
+int excessive_words(int ch, struct param_type *params,
+                    struct readline_type *readline);
 
 void add_word_or_filename(struct w_queue *word_chain,
                           struct dynamic_array *tmp_word,
                           struct param_type *params);
 
 int validate_redirections(int ch, int next_ch, struct param_type *params);
-int is_double_token(struct param_type *params);
 
 int stream_redirect_tokens(struct w_queue *word_chain,
                            struct dynamic_array *tmp_word,
@@ -38,7 +39,7 @@ int pipeline_token_processing(struct w_queue *word_chain,
                               struct param_type *params);
 
 int special_tokens(struct w_queue *word_chain, struct c_queue *cmdlines,
-                   struct dynamic_array *tmp_word, int ch,
+                   struct dynamic_array *tmp_word, int *ch,
                    struct param_type *params, struct readline_type *readline);
 
 #endif
diff --git a/shell.c b/shell.c
index 36eb916..be09e44 100644
--- a/shell.c
+++ b/shell.c
@@ -22,6 +22,7 @@ MAKE_QUEUE_PUSH(c_queue, cmdline, char**)
 MAKE_QUEUE_PUSH(p_queue, pid, int)
 
 enum modes { word_separation, whole_word };
+volatile sig_atomic_t last_execution_status = 0;
 
 static void change_terminal_settings(struct termios *cur_terminal_settings,
                                      struct termios *save_terminal_settings)
@@ -49,11 +50,17 @@ static void show_invitation()
 static void handler(int signal)
 {
     int save_errno = errno;
-    int pid;
+    int pid, result;
 
     if(signal == SIGCHLD) {
         do {
-            pid = wait4(-1, NULL, WNOHANG, NULL);
+            pid = wait4(-1, &result, WNOHANG, NULL);
+            if(pid > 0) {
+                if(WIFEXITED(result))
+                    last_execution_status = WEXITSTATUS(result) == 0 ? 0 : 1;
+                else
+                    last_execution_status = 1;
+            }
         } while(pid > 0);
     }
     errno = save_errno;
@@ -71,12 +78,17 @@ static void init_params(struct param_type *params, enum modes *current_mode)
     params->streams.input_stream = NULL;
     params->streams.output_stream = NULL;
     params->streams.output_stream_to_append = NULL;
-    /* 0 - success, 1 - error */
-    params->last_execution_status = 0;
     params->pipeline = 0;
     params->new_readline = 1;
     params->general_pgid = -1;
+    params->general_pipe_pgid = -1;
+    params->general_subshell_pgid = -1;
+    params->subshell = 0;
+    params->background_process = 0;
+    params->fd_read_for_channel = -1;
+    params->fd_read_for_subshell = -1;
     *current_mode = word_separation;
+    last_execution_status = 0;
 }
 
 static void clear_filename(struct param_type *params)
@@ -105,6 +117,10 @@ static void reset_params(struct param_type *params,
     readline_reset_array(readline);
     clear_filename(params);
     init_params(params, current_mode);
+    if(params->fd_read_for_channel != -1)
+        close(params->fd_read_for_channel);
+    if(params->fd_read_for_subshell != -1)
+        close(params->fd_read_for_subshell);
 }
 
 static void prepare_for_next_command_on_line(struct param_type *params,
@@ -149,6 +165,8 @@ static const char* error_code_to_token(int error_code)
     case err_empty_command:                 return "empty command";
     case err_extra_chars_after_filename:    return "extra chars after filename";
     case err_odd_double_quotes:             return "odd number of double quotes";
+    case err_missing_closing_bracket:       return "missing closing bracket";
+    case err_repeated_background_ch:        return "repeated &";
     }
     return NULL;
 }
@@ -160,24 +178,28 @@ void error_identification(const struct param_type *params)
 
 static int special_token_handling(struct w_queue *word_chain,
                                   struct c_queue *cmdlines,
-                                  struct dynamic_array *tmp_word, int ch,
+                                  struct dynamic_array *tmp_word, int *ch,
                                   struct param_type *params,
                                   struct readline_type *readline)
 {
     return
-        stream_redirect_tokens(word_chain, tmp_word, ch, params, readline) ?
+        stream_redirect_tokens(word_chain, tmp_word, *ch, params, readline) ?
             1 : special_tokens(word_chain, cmdlines, tmp_word, ch, params,
                                readline);
 }
 
 static void wait_for_process_to_complete(struct p_queue *pid_store)
 {
-    int total_process_counter, current_process_counter, wait_pid;
+    int total_process_counter, current_process_counter, wait_pid, result;
     total_process_counter = p_queue_get_process_quantity(pid_store);
     current_process_counter = 0;
 
     do {
-        wait_pid = wait(NULL);
+        wait_pid = wait(&result);
+        if(WIFEXITED(result))
+            last_execution_status = WEXITSTATUS(result) == 0 ? 0 : 1;
+        else
+            last_execution_status = 1;
         if(p_queue_find_pid(pid_store, wait_pid))
             ++current_process_counter;
     } while(total_process_counter != current_process_counter);
@@ -202,23 +224,34 @@ static void close_files(int input_fd, int output_fd)
         close(output_fd);
 }
 
+static int get_true_terminal_fd()
+{
+    if(isatty(0))
+        return 0;
+    else if(isatty(1))
+        return 1;
+    else return 2;
+}
+
 static void postprocessing(struct w_queue *word_chain, struct c_queue *cmdlines,
                            struct p_queue *pid_store, struct param_type *params,
                            int input_fd, int output_fd)
 {
+    int terminal_fd;
     clean_up_memory(word_chain, cmdlines, params);
     close_files(input_fd, output_fd);
-    if(params->tokens != '&') {
+    if(!params->background_process) {
         wait_for_process_to_complete(pid_store);
         signal(SIGTTOU, SIG_IGN);
-        tcsetpgrp(0, getpid());
+        terminal_fd = get_true_terminal_fd();
+        tcsetpgrp(terminal_fd, getpid());
     }
     p_queue_clear(pid_store);
 }
 
 static void set_signal_disposition(struct param_type *params)
 {
-    if(params->tokens == '&')
+    if(params->background_process)
         /* zombie process termination on signal */
         signal(SIGCHLD, handler);
     else
@@ -249,58 +282,146 @@ int is_stream_redirection_set(const struct param_type *params)
             params->streams.output_stream_to_append;
 }
 
+static void identify_general_pipe_pgid(struct param_type *params, int pid)
+{
+    int terminal_fd;
+    if(params->general_pipe_pgid == -1)
+        params->general_pipe_pgid = pid;
+    if(!params->background_process) {
+        /* foreground group */
+        terminal_fd = get_true_terminal_fd();
+        signal(SIGTTOU, SIG_IGN);
+        tcsetpgrp(terminal_fd, params->general_pipe_pgid);
+    }
+}
+
 static void identify_general_pgid(struct param_type *params, int pid)
 {
+    int terminal_fd;
     if(params->general_pgid == -1)
         params->general_pgid = pid;
-    if(params->tokens != '&')
+    if(!params->background_process) {
         /* foreground group */
-        tcsetpgrp(0, params->general_pgid);
+        terminal_fd = get_true_terminal_fd();
+        signal(SIGTTOU, SIG_IGN);
+        tcsetpgrp(terminal_fd, params->general_pgid);
+    }
+}
+
+static int find_subshell_after_pipe(struct readline_type *readline)
+{
+    int i;
+    for(i = readline->considered_index; i <= readline->last_element_index; ++i) {
+        if(readline->arr[i] == ' ')
+            continue;
+        if(readline->arr[i] == '(')
+            return 1;
+        break;
+    }
+    return 0;
+}
+
+static int is_background_command(struct readline_type *readline)
+{
+    int i;
+    for(i = readline->considered_index; i <= readline->last_element_index; ++i){
+        if(readline->arr[i] == '&' && readline->arr[i+1] != '&')
+            return 1;
+        else if(readline->arr[i] == '&' && readline->arr[i+1] == '&')
+            ++i;
+    }
+    return 0;
 }
 
 static void make_pipeline(struct w_queue *word_chain, struct c_queue *cmdlines,
                           struct param_type *params,
+                          struct readline_type *readline,
                           int input_fd, int output_fd)
 {
     struct p_queue pid_store;
     p_queue_init(&pid_store);
     char **cmdline = NULL;
     int fd[2];
-    int save_read_fd, pid;
+    int subshell_fd[2];
+    int save_read_fd, pid, subshell_after;
 
-    pipe(fd);
+    subshell_after = find_subshell_after_pipe(readline);
     cmdline = c_queue_pop(cmdlines);
+
+    if(!c_queue_is_empty(cmdlines))
+        pipe(fd);
+
     set_signal_disposition(params);
+
+#if 0
+    if(params->fd_pipe_rd != -1)
+        /* set foreground group by subshell process */
+        identify_general_pgid(params, params->general_pgid);
+#endif
+
+    if(c_queue_is_empty(cmdlines) && subshell_after)
+        pipe(subshell_fd);
+
     pid = fork();
 
+#if 0
     /* parent process */
     if(pid)
         identify_general_pgid(params, pid);
+#endif
+    if(pid) {
+        /* else set foreground group by first pipe process */
+        if(params->general_pipe_pgid == -1)
+            identify_general_pipe_pgid(params, pid);
+    }
 
     if(pid == 0) {
-        close(fd[0]);
-        dup2(fd[1], 1);
-        close(fd[1]);
-        if(is_stream_redirection_set(params))
+        if(params->fd_read_for_channel != -1) {
+            dup2(params->fd_read_for_channel, 0);
+            close(params->fd_read_for_channel);
+        }
+        if(!c_queue_is_empty(cmdlines)) {
+            close(fd[0]);
+            dup2(fd[1], 1);
+            close(fd[1]);
+        } else if(subshell_after) {
+            close(subshell_fd[0]);
+            dup2(subshell_fd[1], 1);
+            close(subshell_fd[1]);
+        }
+        if(is_stream_redirection_set(params)) {
             change_streams(input_fd, output_fd, 1, 1);
+            if(params->fd_read_for_channel != -1 && c_queue_is_empty(cmdlines))
+                change_streams(input_fd, output_fd, 1, 0);
+        }
         /* change pgid */
-        setpgid(getpid(), params->general_pgid == -1 ?
-                                        getpid() : params->general_pgid);
+        setpgid(getpid(), params->general_pipe_pgid == -1 ? getpid() :
+                                                    params->general_pipe_pgid);
         execvp(cmdline[0], cmdline);
         perror(cmdline[0]);
         exit(1);
     }
-
-    close(fd[1]);
     p_queue_push(&pid_store, pid);
+    if(params->fd_read_for_channel != -1)
+        close(params->fd_read_for_channel);
+
+    if(subshell_after && c_queue_is_empty(cmdlines)) {
+        params->fd_read_for_subshell = subshell_fd[0];
+        close(subshell_fd[1]);
+    }
+
+    if(!c_queue_is_empty(cmdlines))
+        close(fd[1]);
 
     while(!c_queue_is_empty(cmdlines)) {
         cmdline = c_queue_pop(cmdlines);
         /* if not last process in pipeline*/
-        if(!c_queue_is_empty(cmdlines)) {
+        if(!c_queue_is_empty(cmdlines)){
             save_read_fd = fd[0];
             pipe(fd);
-        }
+        } else if(subshell_after)
+            pipe(subshell_fd);
+
         pid = fork();
         if(pid == 0) {
             if(!c_queue_is_empty(cmdlines)) {
@@ -314,13 +435,17 @@ static void make_pipeline(struct w_queue *word_chain, struct c_queue *cmdlines,
                 close(fd[0]);
             }
             /* for last process in pipeline */
-            if(c_queue_is_empty(cmdlines))
+            if(c_queue_is_empty(cmdlines)) {
                 if(is_stream_redirection_set(params))
                     change_streams(input_fd, output_fd, 1, 0);
-
+                if(subshell_after) {
+                    close(subshell_fd[0]);
+                    dup2(subshell_fd[1], 1);
+                    close(subshell_fd[1]);
+                }
+            }
             /* change pgid */
-            setpgid(getpid(), params->general_pgid);
-
+            setpgid(getpid(), params->general_pipe_pgid);
             execvp(cmdline[0], cmdline);
             perror(cmdline[0]);
             exit(1);
@@ -328,12 +453,23 @@ static void make_pipeline(struct w_queue *word_chain, struct c_queue *cmdlines,
         if(!c_queue_is_empty(cmdlines)) {
             close(save_read_fd);
             close(fd[1]);
-        } else
+        } else {
             close(fd[0]);
+            if(subshell_after)
+                close(subshell_fd[1]);
+        }
         p_queue_push(&pid_store, pid);
     }
+    if(subshell_after)
+        params->fd_read_for_subshell = subshell_fd[0];
+    else
+        params->fd_read_for_subshell = -1;
     postprocessing(word_chain, cmdlines, &pid_store, params, input_fd,
                    output_fd);
+#if 0
+    if(!subshell_after)
+        params->general_pgid = -1;
+#endif
 }
 
 static void open_files(const struct param_type *params, int *input_fd,
@@ -380,7 +516,8 @@ static void change_directory(char **cmdline)
 
 static void run_external_program(struct w_queue *word_chain,
                                  struct c_queue *cmdlines,
-                                 struct param_type *params)
+                                 struct param_type *params,
+                                 struct readline_type *readline)
 {
     int pid, input_fd, output_fd;
     struct p_queue pid_store;
@@ -389,6 +526,11 @@ static void run_external_program(struct w_queue *word_chain,
     input_fd = 0;
     output_fd = 0;
 
+    if(is_background_command(readline))
+        params->background_process = 1;
+    else
+        params->background_process = 0;
+
     if(is_stream_redirection_set(params))
         open_files(params, &input_fd, &output_fd);
 
@@ -397,7 +539,8 @@ static void run_external_program(struct w_queue *word_chain,
         return;
     }
     if(params->pipeline) {
-        make_pipeline(word_chain, cmdlines, params, input_fd, output_fd);
+        make_pipeline(word_chain, cmdlines, params, readline,
+                      input_fd, output_fd);
         return;
     }
     cmdline = c_queue_pop(cmdlines);
@@ -410,19 +553,29 @@ static void run_external_program(struct w_queue *word_chain,
             perror("fork error");
             exit(1);
         }
+#if 0
         /* parent process */
         if(pid)
-            identify_general_pgid(params, pid);
+            identify_general_pgid(params, getpid());
+#endif
+
 
         /* child process */
         if(pid == 0) {
             if(is_stream_redirection_set(params))
                 change_streams(input_fd, output_fd, 0, 0);
-            /* change pgid */
-            setpgid(getpid(), params->general_pgid == -1 ?
-                                        getpid() : params->general_pgid);
+            if(params->fd_read_for_channel != -1) {
+                dup2(params->fd_read_for_channel, 0);
+                close(params->fd_read_for_channel);
+            }
+            /* set foreground process */
+            if(params->subshell && params->general_pgid != -1)
+                setpgid(getpid(), params->general_pgid);
+            else {
+                identify_general_pgid(params, getpid());
+                setpgid(getpid(), getpid());
+            }
             execvp(cmdline[0], cmdline);
-            params->last_execution_status = 1;
             perror(cmdline[0]);
             exit(1);
         }
@@ -430,6 +583,11 @@ static void run_external_program(struct w_queue *word_chain,
         p_queue_push(&pid_store, pid);
         postprocessing(word_chain, cmdlines, &pid_store, params, input_fd,
                        output_fd);
+        /* ??? */
+#if 0
+        if(!params->subshell)
+            params->general_pgid = -1;
+#endif
     }
 }
 
@@ -500,10 +658,14 @@ static void generate_readline(struct readline_type *readline)
 {
     struct termios cur_terminal_settings, save_terminal_settings;
     enum keys found_key = none;
-    int match_result;
+    int match_result, terminal_fd;
     char ch;
 
     change_terminal_settings(&cur_terminal_settings, &save_terminal_settings);
+    /* return foreground group by main process */
+    terminal_fd = get_true_terminal_fd();
+    signal(SIGTTOU, SIG_IGN);
+    tcsetpgrp(terminal_fd, getpid());
 
     while((ch = getchar()) && !readline_termination_condition(ch, readline)) {
         if(ch == tab) {
@@ -589,27 +751,41 @@ static void command_processing(struct param_type *params,
     } else if(params->empty_word_flag || params->is_word)
         add_word(word_chain, tmp_word, params);
 
-    if((params->tokens == and || params->tokens == or) &&
-            params->last_execution_status == 1) {
-        /* ??? */
-        fprintf(stderr, "cannot be performed\n");
-        return;
+    if(word_chain->first == NULL && cmdlines->first == NULL) {
+        /* if not ending subshell */
+        if(params->tokens != '(')
+            params->wrong_command = err_empty_command;
+        goto clean;
     }
-
-    if(word_chain->first == NULL) {
-        params->wrong_command = err_empty_command;
+#if 0
+    if((ch == new_line || ch == end_subshell) &&
+            ((params->tokens == and && last_execution_status == 1) ||
+            (params->tokens == or && last_execution_status == 0))) {
+        if(ch == end_subshell && params->subshell)
+            exit(1);
+        params->wrong_command = err_set_failure;
         goto clean;
     }
+#endif
+    /* not subshell process; was &&/|| command\n */
+    if(ch == new_line &&
+            ((params->tokens == and && last_execution_status == 1) ||
+            (params->tokens == or && last_execution_status == 0)))
+        goto clean;
 
-    cmdline = create_cmdline(word_chain, w_queue_get_word_count(word_chain));
-    c_queue_push(cmdlines, cmdline);
-    run_external_program(word_chain, cmdlines, params);
+    if(word_chain->first != NULL) {
+        cmdline = create_cmdline(word_chain, w_queue_get_word_count(word_chain));
+        c_queue_push(cmdlines, cmdline);
+    }
+    run_external_program(word_chain, cmdlines, params, readline);
 
 clean:
     error_identification(params);
+    if(params->tokens == end_subshell && params->subshell)
+        exit(last_execution_status);
     last_token = params->tokens;
 
-    if(last_token == '&' || last_token == 0 || ch == new_line) {
+    if(last_token == 0 || ch == new_line) {
         reset_params(params, current_mode, word_chain, cmdlines, tmp_word,
                      readline);
         show_invitation();
@@ -619,6 +795,99 @@ clean:
                                          tmp_word);
 }
 
+/* searching for the paired closed bracket too */
+static int find_pipeline_after_subshell(struct readline_type *readline,
+                                        struct param_type *params)
+{
+    int i;
+    for(i = readline->considered_index; i <= readline->last_element_index &&
+                                                readline->arr[i] != ')'; ++i)
+    {}
+
+    if(i == readline->last_element_index+1) {
+        params->wrong_command = err_missing_closing_bracket;
+        return 0;
+    }
+    ++i;
+    while(i <= readline->last_element_index) {
+        if(readline->arr[i] == ' ') {
+            ++i;
+            continue;
+        }
+        break;
+    }
+    if(readline->arr[i] == '|')
+        return 1;
+    else
+        return 0;
+}
+
+static void readline_idx_after_subshell(struct readline_type *readline,
+                                        struct param_type *params)
+{
+    int i;
+    for(i = readline->considered_index; i <= readline->last_element_index &&
+                                                readline->arr[i] != ')'; ++i)
+    {}
+
+    if(i == readline->last_element_index + 1) {
+        params->wrong_command = err_missing_closing_bracket;
+        return;
+    }
+
+    ++i;
+    /* skip whitespace symbols */
+    for( ; i <= readline->last_element_index && readline->arr[i] == ' '; ++i)
+    {}
+    readline->considered_index = i;
+}
+
+static void make_subshell(struct readline_type *readline,
+                          struct param_type *params)
+{
+    int fd[2];
+    int pid, pipeline_after, pipeline_before;
+
+    pipeline_after = 0;
+
+    pipeline_after = find_pipeline_after_subshell(readline, params);
+    pipeline_before = params->fd_read_for_subshell != -1 ? 1 : 0;
+
+    if(pipeline_after) {
+        pipe(fd);
+        params->fd_read_for_channel = fd[0];
+    }
+
+    pid = fork();
+    /* child */
+    if(pid == 0) {
+        params->subshell = 1;
+        params->pipeline = 0;
+        if(pipeline_after) {
+            identify_general_pipe_pgid(params, getpid());
+            params->general_pgid = getpid();
+            setpgid(getpid(), params->general_pipe_pgid);
+            close(fd[0]);
+            dup2(fd[1], 1);
+            close(fd[1]);
+        }
+        if(pipeline_before) {
+            dup2(params->fd_read_for_subshell, 0);
+            close(params->fd_read_for_subshell);
+            params->general_pgid = params->general_pipe_pgid;
+            setpgid(getpid(), params->general_pipe_pgid);
+        }
+    /* parent */
+    } else {
+        sleep(1);
+        if(pipeline_after) {
+            close(fd[1]);
+            params->general_pipe_pgid = pid;
+        }
+        readline_idx_after_subshell(readline, params);
+    }
+}
+
 static void word_separation_processing(int ch, struct param_type *params,
                                        enum modes *current_mode,
                                        struct w_queue *word_chain,
@@ -644,15 +913,22 @@ static void word_separation_processing(int ch, struct param_type *params,
         params->escape_sequences = 1;
         return;
     }
-    if(special_token_handling(word_chain, cmdlines, tmp_word, ch, params,
+    if(special_token_handling(word_chain, cmdlines, tmp_word, &ch, params,
                               readline)) {
-        if(command_execution_condition(params))
+        if(command_execution_condition(params, readline))
             command_processing(params, current_mode, word_chain, cmdlines,
                                tmp_word, readline, ch);
+        if(params->tokens == start_subshell)
+            make_subshell(readline, params);
         return;
     }
     if(params->wrong_command) {
         error_identification(params);
+
+        /* subshell termination failed; failure with (&&, ||) too */
+        if(params->subshell)
+            exit(1);
+
         clean_input_buffer();
         reset_params(params, current_mode, word_chain, cmdlines, tmp_word,
                      readline);
@@ -660,9 +936,12 @@ static void word_separation_processing(int ch, struct param_type *params,
         return;
     }
     if(check_separation(ch, *params)) {
-        if(excessive_words(ch, params)) {
+        if(excessive_words(ch, params, readline)) {
             error_identification(params);
             clean_input_buffer();
+            /* subshell termination failed */
+            if(params->subshell)
+                exit(1);
             reset_params(params, current_mode, word_chain, cmdlines, tmp_word,
                          readline);
             show_invitation();
@@ -731,6 +1010,7 @@ int main()
     dynarr_create_array(&tmp_word);
     readline_create_array(&readline);
     init_params(&params, &current_mode);
+    signal(SIGCHLD, handler);
     show_invitation();
     generate_readline(&readline);
 
@@ -747,9 +1027,18 @@ int main()
         else if(current_mode == word_separation) {
             word_separation_processing(ch, &params, &current_mode, &word_chain,
                                        &cmdlines, &tmp_word, &readline);
-            /* double token was found */
-            if(readline.considered_index != i)
-                ++i;
+            if(params.tokens == start_subshell && !params.subshell) {
+                i = readline.considered_index;
+                continue;
+            }
+            /*
+            * either a double token was found
+            * or the subshell part was skipped
+            */
+            if(readline.considered_index != i) {
+                i = readline.considered_index;
+                continue;
+            }
          }
         else if(current_mode == whole_word)
             whole_word_processing(ch, &params, &current_mode, &word_chain,
diff --git a/shell.h b/shell.h
index d1d5a2c..7a5ba3a 100644
--- a/shell.h
+++ b/shell.h
@@ -4,6 +4,8 @@
 #include "dynamic_array.h"
 #include "queue.h"
 
+#include <signal.h>
+
 enum {
     end_of_file     = 4,
     new_line        = 10,
@@ -18,7 +20,10 @@ enum {
 enum {
     append          = '>' + 1,
     and             = '&' + 1,
-    or              = '|' + 1
+    or              = '|' + 1,
+    next_command    = ';',
+    start_subshell  = '(',
+    end_subshell    = ')'
 };
 
 /* error codes */
@@ -29,7 +34,10 @@ enum {
     err_bg_process                  = 4,
     err_empty_command               = 5,
     err_extra_chars_after_filename  = 6,
-    err_odd_double_quotes           = 7
+    err_odd_double_quotes           = 7,
+    err_set_failure                 = 8,
+    err_missing_closing_bracket     = 9,
+    err_repeated_background_ch      = 10
 };
 
 /* storing file names to redirect standard input/output streams */
@@ -48,12 +56,19 @@ struct param_type {
     int tokens;
     int wrong_command;
     struct io_type streams;
-    int last_execution_status;
     int pipeline;
     int new_readline;
+    int general_pipe_pgid;
+    int general_subshell_pgid;
     int general_pgid;
+    int subshell;
+    int fd_read_for_channel;
+    int fd_read_for_subshell;
+    int background_process;
 };
 
+extern volatile sig_atomic_t last_execution_status;
+
 int filename_waiting(struct param_type *params);
 void add_filename(struct dynamic_array *tmp_word, struct param_type *params);
 void add_word(struct w_queue *word_chain, struct dynamic_array *tmp_word,