add output option

Closes #6

src/cli.rs

@@ -36,6 +36,9 @@ pub struct Args {
     #[clap(short = 'f', long, default_value = ".env")]
     pub file: PathBuf,
 
+    #[clap(short = 'o', long)]
+    pub output: Option<PathBuf>,
+
     #[clap(value_parser)]
     pub section_names: Vec<String>,
 }

src/main.rs

@@ -35,7 +35,7 @@ fn main() -> Result<(), Error> {
 fn change_env_layout(args: &cli::Args) -> Result<(), Error> {
     let content = std::fs::read_to_string(&args.file).map_err(|_| Error::OpenFile)?;
 
-    let mut writer = File::create(&args.file)
+    let mut writer = File::create(args.output.as_ref().unwrap_or(&args.file))
         .map_err(|_| Error::OpenFile)
         .map(BufWriter::new)?;