Userspace: Shell now processes $ arguments

userspace/Shell/main.cpp

@@ -1,6 +1,8 @@
+#include <BAN/Optional.h>
 #include <BAN/ScopeGuard.h>
 #include <BAN/String.h>
 #include <BAN/Vector.h>
+
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -10,6 +12,59 @@
 
 struct termios old_termios, new_termios;
 
+BAN::Optional<BAN::String> parse_dollar(BAN::StringView command, size_t& i)
+{
+	ASSERT(command[i] == '$');
+
+	if (++i >= command.size())
+		return "$"sv;
+	
+	if (isalnum(command[i]))
+	{
+		size_t len = 1;
+		for (; i + len < command.size(); len++)
+			if (!isalnum(command[i + len]))
+				break;
+		BAN::String name = command.substring(i, len);
+		i += len - 1;
+
+		if (const char* value = getenv(name.data()))
+			return BAN::StringView(value);
+		return ""sv;
+	}
+	else if (command[i] == '{')
+	{
+		size_t len = 1;
+		for (; i + len < command.size(); len++)
+		{
+			if (command[i + len] == '}')
+				break;
+			if (!isalnum(command[i + len]))
+				return {};
+		}
+
+		if (i + len >= command.size())
+			return {};
+
+		BAN::String name = command.substring(i + 1, len - 1);
+		i += len;
+
+		if (const char* value = getenv(name.data()))
+			return BAN::StringView(value);
+		return ""sv;
+	}
+	else if (command[i] == '[')
+	{
+		return {};
+	}
+	else if (command[i] == '(')
+	{
+		return {};
+	}
+
+	return "$"sv;
+}
+
 BAN::Vector<BAN::String> parse_command(BAN::StringView command)
 {
 	enum class State
@@ -23,8 +78,10 @@ BAN::Vector<BAN::String> parse_command(BAN::StringView command)
 
 	State state = State::Normal;
 	BAN::String current;
-	for (char c : command)
+	for (size_t i = 0; i < command.size(); i++)
 	{
+		char c = command[i];
+
 		switch (state)
 		{
 			case State::Normal:
@@ -32,6 +89,16 @@ BAN::Vector<BAN::String> parse_command(BAN::StringView command)
 					state = State::SingleQuote;
 				else if (c == '"')
 					state = State::DoubleQuote;
+				else if (c == '$')
+				{
+					auto expansion = parse_dollar(command, i);
+					if (!expansion.has_value())
+					{
+						fprintf(stderr, "bad substitution\n");
+						return {};
+					}
+					MUST(current.append(expansion.value()));
+				}
 				else if (!isspace(c))
 					MUST(current.push_back(c));
 				else
@@ -52,8 +119,18 @@ BAN::Vector<BAN::String> parse_command(BAN::StringView command)
 			case State::DoubleQuote:
 				if (c == '"')
 					state = State::Normal;
-				else
+				else if (c != '$')
 					MUST(current.push_back(c));
+				else
+				{
+					auto expansion = parse_dollar(command, i);
+					if (!expansion.has_value())
+					{
+						fprintf(stderr, "bad substitution\n");
+						return {};
+					}
+					MUST(current.append(expansion.value()));
+				}
 				break;
 		}
 	}
@@ -181,7 +258,7 @@ BAN::String get_prompt()
 {
 	const char* raw_prompt = getenv("PS1");
 	if (raw_prompt == nullptr)
-		raw_prompt = "\e[32muser@host\e[m:\e[34m\\~\e[m$ ";
+		return ""sv;
 
 	BAN::String prompt;
 	for (int i = 0; raw_prompt[i]; i++)
@@ -254,6 +331,7 @@ int main(int argc, char** argv)
 {
 	if (argc >= 1)
 		setenv("SHELL", argv[0], true);
+	setenv("PS1", "\e[32muser@host\e[m:\e[34m\\~\e[m$ ", false);
 
 	tcgetattr(0, &old_termios);