feat: add --output option (#43)

Author: koyashiro

Diff for: src/args.rs

@@ -2,6 +2,8 @@ use clap::Parser;
 
 use crate::github_repo::GitHubRepo;
 
+pub const STDIN: &str = "-";
+
 #[derive(Debug, Parser)]
 #[command(author, version, about, long_about = None)]
 pub struct Args {
@@ -19,4 +21,7 @@ pub struct Args {
 
     #[arg(long, value_delimiter = ',')]
     pub repos: Vec<GitHubRepo>,
+
+    #[arg(long, short, default_value = STDIN)]
+    pub output: String,
 }

Diff for: src/main.rs

@@ -5,11 +5,15 @@ mod github_repo;
 mod package_json;
 mod vpm;
 
-use std::io;
+use std::{fs::File, io};
 
 use clap::Parser;
 
-use crate::{args::Args, cache::Cache, generator::VpmRepoGenerator};
+use crate::{
+    args::{Args, STDIN},
+    cache::Cache,
+    generator::VpmRepoGenerator,
+};
 
 #[tokio::main]
 async fn main() -> Result<(), anyhow::Error> {
@@ -32,7 +36,12 @@ async fn main() -> Result<(), anyhow::Error> {
 
     cache.save()?;
 
-    serde_json::to_writer_pretty(io::stdout(), &vpm_repos)?;
+    if args.output.as_str() == STDIN {
+        serde_json::to_writer_pretty(io::stdout(), &vpm_repos)?;
+    } else {
+        let f = File::create(&args.output)?;
+        serde_json::to_writer_pretty(f, &vpm_repos)?;
+    }
 
     Ok(())
 }