Add --only-emit-events

completions/bash

@@ -19,7 +19,7 @@ _watchexec() {
 
     case "${cmd}" in
         watchexec)
-            opts="-w -c -o -W -r -s -k -d -p -n -E -1 -N -e -f -i -v -h -V --watch --clear --on-busy-update --watch-when-idle --restart --signal --kill --stop-signal --stop-timeout --debounce --stdin-quit --no-vcs-ignore --no-project-ignore --no-global-ignore --no-default-ignore --no-discover-ignore --postpone --delay-run --poll --shell --no-shell-long --no-environment --emit-events-to --env --no-process-group --notify --project-origin --workdir --exts --filter --filter-file --ignore --ignore-file --fs-events --no-meta --print-events --verbose --log-file --manual --completions --help --version [COMMAND]..."
+            opts="-w -c -o -W -r -s -k -d -p -n -E -1 -N -e -f -i -v -h -V --watch --clear --on-busy-update --watch-when-idle --restart --signal --kill --stop-signal --stop-timeout --debounce --stdin-quit --no-vcs-ignore --no-project-ignore --no-global-ignore --no-default-ignore --no-discover-ignore --postpone --delay-run --poll --shell --no-shell-long --no-environment --emit-events-to --only-emit-events --env --no-process-group --notify --project-origin --workdir --exts --filter --filter-file --ignore --ignore-file --fs-events --no-meta --print-events --verbose --log-file --manual --completions --help --version [COMMAND]..."
             if [[ ${cur} == -* || ${COMP_CWORD} -eq 1 ]] ; then
                 COMPREPLY=( $(compgen -W "${opts}" -- "${cur}") )
                 return 0

completions/elvish

@@ -66,6 +66,7 @@ set edit:completion:arg-completer[watchexec] = {|@words|
             cand -n 'Don''t use a shell'
             cand --no-shell-long 'Don''t use a shell'
             cand --no-environment 'Shorthand for ''--emit-events=none'''
+            cand --only-emit-events 'Only emit events to stdout, run no commands'
             cand --no-process-group 'Don''t use a process group'
             cand -1 'Testing only: exit Watchexec after the first run'
             cand -N 'Alert when commands start and end'

completions/fish

@@ -33,6 +33,7 @@ complete -c watchexec -s p -l postpone -d 'Wait until first change before runnin
 complete -c watchexec -s n -d 'Don\'t use a shell'
 complete -c watchexec -l no-shell-long -d 'Don\'t use a shell'
 complete -c watchexec -l no-environment -d 'Shorthand for \'--emit-events=none\''
+complete -c watchexec -l only-emit-events -d 'Only emit events to stdout, run no commands'
 complete -c watchexec -l no-process-group -d 'Don\'t use a process group'
 complete -c watchexec -s 1 -d 'Testing only: exit Watchexec after the first run'
 complete -c watchexec -s N -l notify -d 'Alert when commands start and end'

completions/nu

@@ -47,6 +47,7 @@ module completions {
     --no-shell-long           # Don't use a shell
     --no-environment          # Shorthand for '--emit-events=none'
     --emit-events-to: string@"nu-complete watchexec emit_events_to" # Configure event emission
+    --only-emit-events        # Only emit events to stdout, run no commands
     --env(-E): string         # Add env vars to the command
     --no-process-group        # Don't use a process group
     -1                        # Testing only: exit Watchexec after the first run

completions/powershell

@@ -69,6 +69,7 @@ Register-ArgumentCompleter -Native -CommandName 'watchexec' -ScriptBlock {
             [CompletionResult]::new('-n', 'n', [CompletionResultType]::ParameterName, 'Don''t use a shell')
             [CompletionResult]::new('--no-shell-long', 'no-shell-long', [CompletionResultType]::ParameterName, 'Don''t use a shell')
             [CompletionResult]::new('--no-environment', 'no-environment', [CompletionResultType]::ParameterName, 'Shorthand for ''--emit-events=none''')
+            [CompletionResult]::new('--only-emit-events', 'only-emit-events', [CompletionResultType]::ParameterName, 'Only emit events to stdout, run no commands')
             [CompletionResult]::new('--no-process-group', 'no-process-group', [CompletionResultType]::ParameterName, 'Don''t use a process group')
             [CompletionResult]::new('-1', '1', [CompletionResultType]::ParameterName, 'Testing only: exit Watchexec after the first run')
             [CompletionResult]::new('-N', 'N ', [CompletionResultType]::ParameterName, 'Alert when commands start and end')

completions/zsh

@@ -63,6 +63,7 @@ _watchexec() {
 '-n[Don'\''t use a shell]' \
 '--no-shell-long[Don'\''t use a shell]' \
 '--no-environment[Shorthand for '\''--emit-events=none'\'']' \
+'(--completions --manual)--only-emit-events[Only emit events to stdout, run no commands]' \
 '--no-process-group[Don'\''t use a process group]' \
 '-1[Testing only\: exit Watchexec after the first run]' \
 '-N[Alert when commands start and end]' \

crates/cli/src/args.rs

@@ -1,6 +1,6 @@
 use std::{path::PathBuf, str::FromStr, time::Duration};
 
-use clap::{ArgAction, Parser, ValueEnum, ValueHint};
+use clap::{error::ErrorKind, ArgAction, CommandFactory, Parser, ValueEnum, ValueHint};
 use watchexec::paths::PATH_SEPARATOR;
 use watchexec_signals::Signal;
 
@@ -88,7 +88,7 @@ pub struct Args {
 		num_args = 1..,
 		value_hint = ValueHint::CommandString,
 		value_name = "COMMAND",
-		required_unless_present_any = ["completions", "manual"],
+		required_unless_present_any = ["completions", "manual", "only_emit_events"],
 	)]
 	pub command: Vec<String>,
 
@@ -576,9 +576,26 @@ pub struct Args {
 		default_value = "environment",
 		hide_default_value = true,
 		value_name = "MODE",
+		required_if_eq("only_emit_events", "true"),
 	)]
 	pub emit_events_to: EmitEvents,
 
+	/// Only emit events to stdout, run no commands.
+	///
+	/// This is a convenience option for using Watchexec as a file watcher, without running any
+	/// commands. It is almost equivalent to using `cat` as the command, except that it will not
+	/// spawn a new process for each event.
+	///
+	/// This option requires `--emit-events-to` to be set, and restricts the available modes to
+	/// `stdin` and `json-stdin`, modifying their behaviour to write to stdout instead of the stdin
+	/// of the command.
+	#[arg(
+		long,
+		help_heading = OPTSET_COMMAND,
+		conflicts_with_all = ["command", "completions", "manual"],
+	)]
+	pub only_emit_events: bool,
+
 	/// Add env vars to the command
 	///
 	/// This is a convenience option for setting environment variables for the command, without
@@ -936,6 +953,19 @@ pub fn get_args() -> Args {
 		];
 	}
 
+	if args.only_emit_events
+		&& !matches!(
+			args.emit_events_to,
+			EmitEvents::JsonStdin | EmitEvents::Stdin
+		) {
+		Args::command()
+			.error(
+				ErrorKind::InvalidValue,
+				"only-emit-events requires --emit-events-to=stdin or --emit-events-to=json-stdin",
+			)
+			.exit();
+	}
+
 	debug!(?args, "got arguments");
 	args
 }

crates/cli/src/config.rs

@@ -24,7 +24,7 @@ use watchexec::{
 use watchexec_events::{Event, Keyboard, ProcessEnd, Tag};
 use watchexec_signals::Signal;
 
-use crate::state::State;
+use crate::{state::State, emits::events_to_simple_format};
 use crate::{
 	args::{Args, ClearMode, EmitEvents, OnBusyUpdate},
 	state::RotatingTempFile,
@@ -73,20 +73,68 @@ pub fn make_config(args: &Args, state: &State) -> Result<Config> {
 		config.file_watcher(Watcher::Poll(interval.0));
 	}
 
+	let once = args.once;
 	let clear = args.screen_clear;
+
+	let emit_events_to = args.emit_events_to;
+	let emit_file = state.emit_file.clone();
+
+	if args.only_emit_events {
+		config.on_action(move |mut action| {
+			// if we got a terminate or interrupt signal, quit
+			if action.signals().any(|sig| sig == Signal::Terminate || sig == Signal::Interrupt) {
+				action.quit();
+				return action;
+			}
+
+			// clear the screen before printing events
+			if let Some(mode) = clear {
+				match mode {
+					ClearMode::Clear => {
+						clearscreen::clear().ok();
+					}
+					ClearMode::Reset => {
+						for cs in [
+							ClearScreen::WindowsCooked,
+							ClearScreen::WindowsVt,
+							ClearScreen::VtLeaveAlt,
+							ClearScreen::VtWellDone,
+							ClearScreen::default(),
+						] {
+							cs.clear().ok();
+						}
+					}
+				}
+			}
+
+			match emit_events_to {
+				EmitEvents::Stdin => {
+					println!("{}", events_to_simple_format(action.events.as_ref()).unwrap_or_default());
+				}
+				EmitEvents::JsonStdin => {
+					for event in action.events.iter().filter(|e| !e.is_empty()) {
+						println!("{}", serde_json::to_string(event).unwrap_or_default());
+					}
+				}
+				other => unreachable!("emit_events_to should have been validated earlier: {:?}", other),
+			}
+
+			action
+		});
+
+		return Ok(config);
+	}
+
 	let delay_run = args.delay_run.map(|ts| ts.0);
 	let on_busy = args.on_busy_update;
 
 	let signal = args.signal;
 	let stop_signal = args.stop_signal;
 	let stop_timeout = args.stop_timeout.0;
 
-	let once = args.once;
 	let notif = args.notify;
 	let print_events = args.print_events;
 
-	let emit_events_to = args.emit_events_to;
-	let emit_file = state.emit_file.clone();
 	let workdir = Arc::new(args.workdir.clone());
 
 	let mut add_envs = HashMap::new();

crates/cli/src/emits.rs

@@ -12,7 +12,7 @@ pub fn emits_to_environment(events: &[Event]) -> impl Iterator<Item = (String, O
 		.map(|(k, v)| (format!("WATCHEXEC_{k}_PATH"), v))
 }
 
-fn events_to_simple_format(events: &[Event]) -> Result<String> {
+pub fn events_to_simple_format(events: &[Event]) -> Result<String> {
 	let mut buf = String::new();
 	for event in events {
 		let feks = event

doc/watchexec.1

@@ -4,7 +4,7 @@
 .SH NAME
 watchexec \- Execute commands when watched files change
 .SH SYNOPSIS
-\fBwatchexec\fR [\fB\-w\fR|\fB\-\-watch\fR] [\fB\-c\fR|\fB\-\-clear\fR] [\fB\-o\fR|\fB\-\-on\-busy\-update\fR] [\fB\-r\fR|\fB\-\-restart\fR] [\fB\-s\fR|\fB\-\-signal\fR] [\fB\-\-stop\-signal\fR] [\fB\-\-stop\-timeout\fR] [\fB\-d\fR|\fB\-\-debounce\fR] [\fB\-\-stdin\-quit\fR] [\fB\-\-no\-vcs\-ignore\fR] [\fB\-\-no\-project\-ignore\fR] [\fB\-\-no\-global\-ignore\fR] [\fB\-\-no\-default\-ignore\fR] [\fB\-\-no\-discover\-ignore\fR] [\fB\-p\fR|\fB\-\-postpone\fR] [\fB\-\-delay\-run\fR] [\fB\-\-poll\fR] [\fB\-\-shell\fR] [\fB\-n \fR] [\fB\-\-no\-environment\fR] [\fB\-\-emit\-events\-to\fR] [\fB\-E\fR|\fB\-\-env\fR] [\fB\-\-no\-process\-group\fR] [\fB\-N\fR|\fB\-\-notify\fR] [\fB\-\-project\-origin\fR] [\fB\-\-workdir\fR] [\fB\-e\fR|\fB\-\-exts\fR] [\fB\-f\fR|\fB\-\-filter\fR] [\fB\-\-filter\-file\fR] [\fB\-i\fR|\fB\-\-ignore\fR] [\fB\-\-ignore\-file\fR] [\fB\-\-fs\-events\fR] [\fB\-\-no\-meta\fR] [\fB\-\-print\-events\fR] [\fB\-v\fR|\fB\-\-verbose\fR]... [\fB\-\-log\-file\fR] [\fB\-\-manual\fR] [\fB\-\-completions\fR] [\fB\-h\fR|\fB\-\-help\fR] [\fB\-V\fR|\fB\-\-version\fR] [\fICOMMAND\fR] 
+\fBwatchexec\fR [\fB\-w\fR|\fB\-\-watch\fR] [\fB\-c\fR|\fB\-\-clear\fR] [\fB\-o\fR|\fB\-\-on\-busy\-update\fR] [\fB\-r\fR|\fB\-\-restart\fR] [\fB\-s\fR|\fB\-\-signal\fR] [\fB\-\-stop\-signal\fR] [\fB\-\-stop\-timeout\fR] [\fB\-d\fR|\fB\-\-debounce\fR] [\fB\-\-stdin\-quit\fR] [\fB\-\-no\-vcs\-ignore\fR] [\fB\-\-no\-project\-ignore\fR] [\fB\-\-no\-global\-ignore\fR] [\fB\-\-no\-default\-ignore\fR] [\fB\-\-no\-discover\-ignore\fR] [\fB\-p\fR|\fB\-\-postpone\fR] [\fB\-\-delay\-run\fR] [\fB\-\-poll\fR] [\fB\-\-shell\fR] [\fB\-n \fR] [\fB\-\-no\-environment\fR] [\fB\-\-emit\-events\-to\fR] [\fB\-\-only\-emit\-events\fR] [\fB\-E\fR|\fB\-\-env\fR] [\fB\-\-no\-process\-group\fR] [\fB\-N\fR|\fB\-\-notify\fR] [\fB\-\-project\-origin\fR] [\fB\-\-workdir\fR] [\fB\-e\fR|\fB\-\-exts\fR] [\fB\-f\fR|\fB\-\-filter\fR] [\fB\-\-filter\-file\fR] [\fB\-i\fR|\fB\-\-ignore\fR] [\fB\-\-ignore\-file\fR] [\fB\-\-fs\-events\fR] [\fB\-\-no\-meta\fR] [\fB\-\-print\-events\fR] [\fB\-v\fR|\fB\-\-verbose\fR]... [\fB\-\-log\-file\fR] [\fB\-\-manual\fR] [\fB\-\-completions\fR] [\fB\-h\fR|\fB\-\-help\fR] [\fB\-V\fR|\fB\-\-version\fR] [\fICOMMAND\fR] 
 .SH DESCRIPTION
 Execute commands when watched files change.
 .PP
@@ -341,6 +341,13 @@ environment variable.
 
 Finally, the special \*(Aqnone\*(Aq mode will disable event emission entirely.
 .TP
+\fB\-\-only\-emit\-events\fR
+Only emit events to stdout, run no commands.
+
+This is a convenience option for using Watchexec as a file watcher, without running any commands. It is almost equivalent to using `cat` as the command, except that it will not spawn a new process for each event.
+
+This option requires `\-\-emit\-events\-to` to be set, and restricts the available modes to `stdin` and `json\-stdin`, modifying their behaviour to write to stdout instead of the stdin of the command.
+.TP
 \fB\-E\fR, \fB\-\-env\fR=\fIKEY=VALUE\fR
 Add env vars to the command
 

doc/watchexec.1.md

@@ -13,9 +13,10 @@ watchexec - Execute commands when watched files change
 \[**\--no-discover-ignore**\] \[**-p**\|**\--postpone**\]
 \[**\--delay-run**\] \[**\--poll**\] \[**\--shell**\] \[**-n **\]
 \[**\--no-environment**\] \[**\--emit-events-to**\]
-\[**-E**\|**\--env**\] \[**\--no-process-group**\]
-\[**-N**\|**\--notify**\] \[**\--project-origin**\] \[**\--workdir**\]
-\[**-e**\|**\--exts**\] \[**-f**\|**\--filter**\] \[**\--filter-file**\]
+\[**\--only-emit-events**\] \[**-E**\|**\--env**\]
+\[**\--no-process-group**\] \[**-N**\|**\--notify**\]
+\[**\--project-origin**\] \[**\--workdir**\] \[**-e**\|**\--exts**\]
+\[**-f**\|**\--filter**\] \[**\--filter-file**\]
 \[**-i**\|**\--ignore**\] \[**\--ignore-file**\] \[**\--fs-events**\]
 \[**\--no-meta**\] \[**\--print-events**\]
 \[**-v**\|**\--verbose**\]\... \[**\--log-file**\] \[**\--manual**\]
@@ -458,6 +459,19 @@ file with the \$WATCHEXEC_EVENTS_FILE environment variable.
 
 Finally, the special none mode will disable event emission entirely.
 
+**\--only-emit-events**
+
+:   Only emit events to stdout, run no commands.
+
+This is a convenience option for using Watchexec as a file watcher,
+without running any commands. It is almost equivalent to using \`cat\`
+as the command, except that it will not spawn a new process for each
+event.
+
+This option requires \`\--emit-events-to\` to be set, and restricts the
+available modes to \`stdin\` and \`json-stdin\`, modifying their
+behaviour to write to stdout instead of the stdin of the command.
+
 **-E**, **\--env**=*KEY=VALUE*
 
 :   Add env vars to the command