shasum: Support `-o` in hash mode

Fixes #32

src/cmd/shasum.rs

@@ -1,15 +1,16 @@
 use std::{
     fs::File,
-    io::{BufRead, BufReader, Read},
+    io::{stdout, BufRead, BufReader, Read, Write},
     path::{Path, PathBuf},
 };
 
 use anyhow::{anyhow, bail, Context, Result};
 use argp::FromArgs;
 use owo_colors::{OwoColorize, Stream};
+use path_slash::PathExt;
 use sha1::{Digest, Sha1};
 
-use crate::util::file::{open_file, process_rsp, touch};
+use crate::util::file::{buf_writer, open_file, process_rsp, touch};
 
 #[derive(FromArgs, PartialEq, Eq, Debug)]
 /// Print or check SHA1 (160-bit) checksums.
@@ -22,7 +23,8 @@ pub struct Args {
     /// path to input file(s)
     files: Vec<PathBuf>,
     #[argp(option, short = 'o')]
-    /// touch output file on successful check
+    /// (check) touch output file on successful check
+    /// (hash) write hash(es) to output file
     output: Option<PathBuf>,
     #[argp(switch, short = 'q')]
     /// only print failures and a summary
@@ -32,18 +34,29 @@ pub struct Args {
 const DEFAULT_BUF_SIZE: usize = 8192;
 
 pub fn run(args: Args) -> Result<()> {
+    if args.check {
+        for path in process_rsp(&args.files)? {
+            let file = open_file(&path)?;
+            check(&args, &mut BufReader::new(file))?;
+        }
+        if let Some(out_path) = &args.output {
+            touch(out_path)
+                .with_context(|| format!("Failed to touch output file '{}'", out_path.display()))?;
+        }
+    } else {
+        let mut w: Box<dyn Write> =
+            if let Some(out_path) = &args.output {
+                Box::new(buf_writer(out_path).with_context(|| {
+                    format!("Failed to open output file '{}'", out_path.display())
+                })?)
+            } else {
+                Box::new(stdout())
+            };
         for path in process_rsp(&args.files)? {
             let mut file = open_file(&path)?;
-        if args.check {
-            check(&args, &mut BufReader::new(file))?
-        } else {
-            hash(&mut file, &path)?
+            hash(w.as_mut(), &mut file, &path)?
         }
     }
-    if let Some(out_path) = args.output {
-        touch(&out_path)
-            .with_context(|| format!("Failed to touch output file '{}'", out_path.display()))?;
-    }
     Ok(())
 }
 
@@ -98,13 +111,16 @@ where R: BufRead + ?Sized {
     Ok(())
 }
 
-fn hash<R>(reader: &mut R, path: &Path) -> Result<()>
-where R: Read + ?Sized {
+fn hash<R, W>(w: &mut W, reader: &mut R, path: &Path) -> Result<()>
+where
+    R: Read + ?Sized,
+    W: Write + ?Sized,
+{
     let hash = file_sha1(reader)?;
     let mut hash_buf = [0u8; 40];
     let hash_str = base16ct::lower::encode_str(&hash, &mut hash_buf)
         .map_err(|e| anyhow!("Failed to encode hash: {e}"))?;
-    println!("{}  {}", hash_str, path.display());
+    writeln!(w, "{}  {}", hash_str, path.to_slash_lossy())?;
     Ok(())
 }