Take input either from stdin or the first argument

Author: jtdowney

src/main.rs

@@ -1,18 +1,20 @@
 use anyhow::Context;
 use minijinja::Environment;
-use std::{collections::HashMap, env, fs, process};
+use std::{
+    collections::HashMap,
+    env, fs,
+    io::{self, Read},
+};
 
 fn main() -> anyhow::Result<()> {
-    let mut args = env::args();
-    if args.len() != 2 {
-        let name = args.next().unwrap();
-        eprintln!("Usage: {} <template_file>", name);
-        process::exit(1);
-    }
-
-    let path = args.nth(1).unwrap();
-    let template = fs::read_to_string(&path)
-        .with_context(|| format!("Failed to read template file: {}", path))?;
+    let template = if let Some(path) = env::args().nth(1) {
+        fs::read_to_string(&path)
+            .with_context(|| format!("Failed to read template file: {}", path))?
+    } else {
+        let mut input = String::new();
+        io::stdin().read_to_string(&mut input)?;
+        input
+    };
 
     let mut env = Environment::new();
     env.add_template("template", &template)?;

tests/integration_test.rs

@@ -1,5 +1,6 @@
 use std::fs;
-use std::process::Command;
+use std::io::Write;
+use std::process::{Command, Stdio};
 use tempfile::tempdir;
 
 #[test]
@@ -46,3 +47,23 @@ fn test_filters() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_stdin_input() -> anyhow::Result<()> {
+    let mut child = Command::new("cargo")
+        .arg("run")
+        .arg("--")
+        .env("NAME", "World")
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .spawn()?;
+
+    let stdin = child.stdin.as_mut().unwrap();
+    stdin.write_all(b"Hello {{NAME}}!")?;
+
+    let output = child.wait_with_output()?;
+    assert!(output.status.success());
+    assert_eq!(String::from_utf8(output.stdout)?, "Hello World!\n");
+
+    Ok(())
+}