fix: print help text instead of segfaulting when run without arguments

Fixes #3.

src/main.zig

@@ -8,15 +8,26 @@ pub fn main() !void {
     var area = heap.ArenaAllocator.init(gpa.allocator());
     defer area.deinit();
 
+    const help_text = "usage: sp <word>\n\t<word> is the word to check with ispell\n\t<word> can also be piped instead\n";
+
     const allocator = area.allocator();
     const stdin = std.io.getStdIn().reader();
     const stat = try std.io.getStdIn().stat();
     var word: []const u8 = undefined;
 
+    // prepare for writing output to stdout
+    const stdout_file = std.io.getStdOut().writer();
+    var bw = std.io.bufferedWriter(stdout_file);
+    const stdout_writer = bw.writer();
+
     switch (stat.kind) {
         .named_pipe => {
             if (try stdin.readUntilDelimiterOrEofAlloc(allocator, '\n', 1024)) |input| {
                 word = input;
+            } else {
+                _ = try stdout_writer.write(help_text); // output help
+                try bw.flush(); // don't forget to flush!
+                os.exit(1);
             }
         },
         else => {
@@ -26,6 +37,10 @@ pub fn main() !void {
             const next = arg_iterator.next();
             if (next) |input| {
                 word = input;
+            } else {
+                _ = try stdout_writer.write(help_text); // output help
+                try bw.flush(); // don't forget to flush!
+                os.exit(1);
             }
         },
     }
@@ -71,11 +86,6 @@ pub fn main() !void {
     std.mem.copy(u8, content, output[start_idx .. output.len - 1]);
     defer allocator.free(content);
 
-    // prepare for writing output to stdout
-    const stdout_file = std.io.getStdOut().writer();
-    var bw = std.io.bufferedWriter(stdout_file);
-    const stdout_writer = bw.writer();
-
     if (content[0] == '*' or content[0] == '+') {
         // given word was correct so just return the input as no replacement is necessary
         try stdout_writer.print("{s}", .{word});