works

src/main.rs

@@ -1,3 +1,22 @@
-fn main() {
-    println!("Hello, world!");
+use jsonformat::format_json;
+use std::fs;
+use std::io;
+use std::io::Read;
+
+fn main() -> Result<(), io::Error> {
+    let filename = std::env::args().skip(1).next();
+
+    let str = match filename {
+        Some(path) => fs::read_to_string(path)?,
+        None => {
+            let mut buf = String::new();
+            let stdin = std::io::stdin();
+            stdin.lock().read_to_string(&mut buf)?;
+            buf
+        }
+    };
+
+    println!("{}", format_json(&str, "  "));
+
+    Ok(())
 }