By default, only report progress when stderr is a terminal

Can be overridden by --progress=[true/false/auto]. Previous
option --quiet hidden, but kept for compatibility.

fclones/src/config.rs

@@ -749,8 +749,16 @@ const fn after_help() -> &'static str {
 #[derive(clap::Parser, Debug)]
 #[command(about, author, version, after_help = after_help(), max_term_width = 100)]
 pub struct Config {
-    /// Suppress progress reporting
-    #[arg(short('q'), long)]
+    /// Override progress reporting, by default (=auto) only report when stderr is a terminal.
+    /// Possible values: true, false, auto.
+    #[arg(long, value_name = "VAL", require_equals = true,
+          value_parser(["auto", "true", "false"]), default_value = "auto",
+
+          hide_possible_values = true, hide_default_value = true)]
+    pub progress: String,
+
+    // compatibility with fclones <= 0.34, overrides --progress
+    #[arg(short('q'), long, hide = true)]
     pub quiet: bool,
 
     /// Find files

fclones/src/main.rs

@@ -1,7 +1,7 @@
 use std::collections::HashMap;
 use std::ffi::{OsStr, OsString};
 use std::fs::File;
-use std::io::{stdin, Write};
+use std::io::{stderr, stdin, IsTerminal, Write};
 use std::process::exit;
 use std::sync::Arc;
 use std::{fs, io};
@@ -251,9 +251,12 @@ fn main() {
     }
 
     let mut log = StdLog::new();
-    if config.quiet {
-        log.no_progress = true;
-    }
+    log.no_progress = match (config.quiet, config.progress.as_str()) {
+        (true, _) => true,
+        (_, "false") => true,
+        (_, "true") => false,
+        (_, _auto) => !stderr().is_terminal(),
+    };
 
     let cwd = match std::env::current_dir() {
         Ok(cwd) => cwd,