Get current juliaup channel with juliaup self channel

src/bin/juliainstaller.rs

@@ -509,7 +509,7 @@ pub fn main() -> Result<()> {
         run_command_config_modifypath(Some(install_choices.modifypath), true, &paths).unwrap();
     }
     run_command_config_symlinks(Some(install_choices.symlinks), true, &paths).unwrap();
-    run_command_selfchannel(args.juliaup_channel, &paths).unwrap();
+    run_command_selfchannel(Some(args.juliaup_channel), &paths).unwrap();
 
     run_command_add(&args.default_channel, &paths)
         .with_context(|| "Failed to run `run_command_add`.")?;

src/cli.rs

@@ -103,11 +103,10 @@ pub enum SelfSubCmd {
     /// Update the Julia versions database and juliaup itself
     Update {},
     #[cfg(feature = "selfupdate")]
-    #[command(arg_required_else_help = true)]
-    /// Configure the channel to use for juliaup updates.
+    /// Configure the channel to use for juliaup updates. Leave CHANNEL blank to see current channel.
     Channel {
         #[arg(value_enum)]
-        channel: JuliaupChannel,
+        channel: Option<JuliaupChannel>,
     },
     #[cfg(feature = "selfupdate")]
     /// Uninstall this version of juliaup from the system

src/command_selfchannel.rs

@@ -3,7 +3,7 @@ use anyhow::Result;
 
 #[cfg(feature = "selfupdate")]
 pub fn run_command_selfchannel(
-    channel: crate::cli::JuliaupChannel,
+    channel: Option<crate::cli::JuliaupChannel>,
     paths: &crate::global_paths::GlobalPaths,
 ) -> Result<()> {
     use crate::config_file::{load_mut_config_db, save_config_db};
@@ -12,10 +12,19 @@ pub fn run_command_selfchannel(
     let mut config_file = load_mut_config_db(paths)
         .with_context(|| "`self update` command failed to load configuration data.")?;
 
-    config_file.self_data.juliaup_channel = Some(channel.to_lowercase().to_string());
-
-    save_config_db(&mut config_file)
-        .with_context(|| "`selfchannel` command failed to save configuration db.")?;
+    match channel {
+        Some(chan) => {
+            config_file.self_data.juliaup_channel = Some(chan.to_lowercase().to_string());
+            save_config_db(&mut config_file)?;
+        }
+        None => {
+            let channel_name = config_file
+                .self_data
+                .juliaup_channel
+                .expect("juliaup_channel should not be empty.");
+            println!("Your juliaup is currently on channel `{}`. Run `juliaup self channel -h` for help on how to set the juliaup channel.", channel_name);
+        }
+    }
 
     Ok(())
 }