add shebang support (#274)

* add shebang support

cmd/tengo/main.go

@@ -67,6 +67,10 @@ func main() {
 			os.Exit(1)
 		}
 	} else if filepath.Ext(inputFile) == sourceFileExt {
+		if len(inputData) > 1 &&
+			bytes.Compare(inputData[:2], []byte("#!")) == 0 {
+			copy(inputData, "//")
+		}
 		err := CompileAndRun(modules, inputData, inputFile)
 		if err != nil {
 			_, _ = fmt.Fprintln(os.Stderr, err.Error())

docs/tengo-cli.md

@@ -30,6 +30,28 @@ tengo -o myapp myapp.tengo   # compile 'myapp.tengo' into binary file 'myapp'
 tengo myapp                  # execute the compiled binary `myapp`
 ```
 
+Or, you can make tengo source file executable
+
+```bash
+# copy tengo executable to a dir where PATH environment variable includes
+cp tengo /usr/local/bin/
+
+# add shebang line to source file
+cat > myapp.tengo << EOF
+#!/usr/local/bin/tengo
+fmt := import("fmt")
+fmt.println("Hello World!")
+EOF
+
+# make myapp.tengo file executable
+chmod +x myapp.tengo
+
+# run your script
+./myapp.tengo
+```
+
+**Note: Your source file must have `.tengo` extension.**
+
 ## Tengo REPL
 
 You can run Tengo [REPL](https://en.wikipedia.org/wiki/Read–eval–print_loop)