Refactor and improve shell greatly.

doc/user-guide

@@ -108,7 +108,7 @@ supported:
 * Line editing.
 * History.
 * Background tasks ('&').
-* Standard output redirection ('>').
+* Standard redirection ('<', '>', '>>').
 * Piping stdout from a task to stdin of another ('|').
 * Stopping the currently running task (Control-C, '^C').
 * Waiting for a task to complete and executing the next (';').
@@ -130,13 +130,27 @@ supported:
 * Go to start of line (Control-A, '^A', Home).
 * Go to end of line (Control-E, '^E', End).
 * Move between words (Control-arrows).
+* Quotes (''') ('"').
 
 These features are missing from the shell:
 
-* Input redirection ('<') ('<<').
-* Quotes (''') ('"').
+* Proper recursive shell grammar parsing.
+* Heredoc sequences.
+* Command substitution ('$(ls)', '`ls`').
+* Arithmetic expansion ('$((2 + 2))').
+* Aliases.
+* Conditions and loops ('if', 'case', 'while', 'until', 'for').
+* Functions.
+* Some special parameters ('$@', '$*', '$#', '$-', '$!).
+* Special shell variables ('$ENV', '$IFS', '$LINENO').
+* Shell prompt customization ('$PS1', '$PS2', '$PS4').
+* Tilde expansion ('~/foo').
+* Any but the simplest variant of Parameter Expansion.
 * Proper shell wildcard support ('*/*.foo').
-* Escaping newline characters.
+* Ability for variables to not be exported.
+* Export keyword ('export FOO', 'export BAR=bar').
+* Subshells.
+* Proper redirection to/from specific file descriptors.
 * And much more; the shell remains hacky.
 
 If a better shell is installed, and the shell is non-interactive, then the sh

sh/util.cpp

@@ -35,3 +35,105 @@ const char* getenv_safe(const char* name, const char* def)
 	const char* ret = getenv(name);
 	return ret ? ret : def;
 }
+
+bool array_add(void*** array_ptr,
+               size_t* used_ptr,
+               size_t* length_ptr,
+               void* value)
+{
+	void** array;
+	memcpy(&array, array_ptr, sizeof(array)); // Strict aliasing.
+
+	if ( *used_ptr == *length_ptr )
+	{
+		// TODO: Avoid overflow.
+		size_t new_length = 2 * *length_ptr;
+		if ( !new_length )
+			new_length = 16;
+		// TODO: Avoid overflow and use reallocarray.
+		size_t new_size = new_length * sizeof(void*);
+		void** new_array = (void**) realloc(array, new_size);
+		if ( !new_array )
+			return false;
+		array = new_array;
+		memcpy(array_ptr, &array, sizeof(array)); // Strict aliasing.
+		*length_ptr = new_length;
+	}
+
+	memcpy(array + (*used_ptr)++, &value, sizeof(value)); // Strict aliasing.
+
+	return true;
+}
+
+void stringbuf_begin(struct stringbuf* buf)
+{
+	buf->length = 0;
+	buf->allocated_size = 32;
+	if ( !(buf->string = (char*) malloc(buf->allocated_size)) )
+	{
+		buf->allocated_size = 0;
+		return;
+	}
+	buf->string[0] = '\0';
+}
+
+bool might_need_shell_quote(char c)
+{
+	switch ( c )
+	{
+	case '|':
+	case '&':
+	case ';':
+	case '<':
+	case '>':
+	case '(':
+	case ')':
+	case '$':
+	case '`':
+	case '\\':
+	case '"':
+	case '\'':
+	case ' ':
+	case '\t':
+	case '*':
+	case '?':
+	case '[':
+	case '#':
+	case '~':
+	case '=':
+	case '%':
+		return true;
+	default:
+		return false;
+	}
+}
+
+void stringbuf_append_c(struct stringbuf* buf, char c)
+{
+	if ( !buf->string )
+		return;
+	if ( buf->length + 1 == buf->allocated_size )
+	{
+		// TODO: Avoid overflow.
+		size_t new_allocated_size = 2 * buf->allocated_size;
+		char* new_string = (char*) realloc(buf->string, new_allocated_size);
+		if ( !new_string )
+		{
+			buf->string = NULL;
+			buf->length = 0;
+			buf->allocated_size = 0;
+			return;
+		}
+		buf->string = new_string;
+		buf->allocated_size = new_allocated_size;
+	}
+	buf->string[buf->length++] = c;
+	buf->string[buf->length] = '\0';
+}
+
+char* stringbuf_finish(struct stringbuf* buf)
+{
+	if ( !buf->string )
+		return NULL;
+	return buf->string;
+}

sh/util.h

@@ -25,5 +25,21 @@
 
 char* strdup_safe(const char* string);
 const char* getenv_safe(const char* name, const char* def = "");
+bool array_add(void*** array_ptr,
+               size_t* used_ptr,
+               size_t* length_ptr,
+               void* value);
+bool might_need_shell_quote(char c);
+
+struct stringbuf
+{
+	char* string;
+	size_t length;
+	size_t allocated_size;
+};
+
+void stringbuf_begin(struct stringbuf* buf);
+void stringbuf_append_c(struct stringbuf* buf, char c);
+char* stringbuf_finish(struct stringbuf* buf);
 
 #endif