diff --git a/README.md b/README.md
index 4287d941..f2139b8d 100644
--- a/README.md
+++ b/README.md
@@ -364,7 +364,6 @@ _.oO(What should "sed" have looked like by now?)_
 - Let Pattern, replacement, and globs come from a file
 - Let pattern and glob be javascript code returning a string as the result
 - Auto string search / replace if no regex magic is used (and verify that speed is better)
-- Error != warning
 - Flag for String-literal (no regex, no special chars, no escape chars) to avoid backslashes or remembering which characters needs to be escaped
 - Check if https://github.com/eugeneware/replacestream is good to rely on
 - Check if regex engine from spider monkey can be wrapped in something that does not need node
diff --git a/src/engine.ts b/src/engine.ts
index 73b04528..15ceacda 100644
--- a/src/engine.ts
+++ b/src/engine.ts
@@ -6,7 +6,7 @@ const globs = require('fast-glob');
 
 const now = new Date();
 
-import {outputConfig, step, debug, chat, info, error, die} from './output.ts';
+import {outputConfig, step, debug, chat, info, warn, error, die} from './output.ts';
 
 const re = {
 	euro: /€/g,
@@ -156,6 +156,18 @@ function handlePipedData(config) {
 	step('Check Piped Data');
 
 	if (config.includeGlob.length) {
+		if (
+			!config.replacementJs &&
+			!config.replacementPipe &&
+			!config.pipedDataUsed &&
+			!config.voidPipe &&
+			config.pipedData &&
+			config.pipedData !== '\n' &&
+			config.pipedData !== '\r\n'
+		) {
+			warn('Data is piped in, but no flag tells what to do with it. It is not used.');
+		}
+
 		if (!config.replacementJs && config.pipedData) {
 			chat('Piped data never used.');
 		}
diff --git a/src/output.ts b/src/output.ts
index e3f8d6ab..9a1b67d1 100644
--- a/src/output.ts
+++ b/src/output.ts
@@ -1,5 +1,5 @@
 let font: any = {};
-font.red = font.green = font.gray = (str) => str;
+font.yellow = font.red = font.green = font.gray = (str) => str;
 // check for node version supporting chalk - if so overwrite `font`
 //const font = import('chalk');
 
@@ -42,6 +42,14 @@ export const error = function (msg, data = '') {
 	return false;
 };
 
+export const warn = function (msg, data = '') {
+	if (config?.quiet || config?.quietTotal) {
+		return false;
+	}
+	console.error(...[' 🟡', font.yellow(msg), data].filter(Boolean));
+	return false;
+};
+
 export function debug(data) {
 	if (config.debug) {
 		console.error(font.gray(JSON.stringify(data, null, 4)));
diff --git a/test/cli/run.sh b/test/cli/run.sh
index bca55aaa..5462d834 100644
--- a/test/cli/run.sh
+++ b/test/cli/run.sh
@@ -293,6 +293,28 @@ assert		 		"printf x | rexreplace 'foo' 'pipe' my.file -o --replacement-js --voi
 assert_failure		"printf x | rexreplace 'b' _ my.file -P -R"
 assert_failure		"printf x | rexreplace 'b' _ my.file -P -T"
 
+# Warn when piped data is not used (#719)
+reset
+assert		 		"printf notes | rexreplace foo bar my.file 2>&1 1>/dev/null"    " 🟡 Data is piped in, but no flag tells what to do with it. It is not used.\nmy.file "
+assert		 		"cat my.file"    'barbar'
+
+reset
+assert		 		"printf notes | rexreplace foo bar my.file -q 2>&1 1>/dev/null"    ''
+
+reset
+assert		 		"printf notes | rexreplace foo bar my.file -Q 2>&1 1>/dev/null"    ''
+
+reset
+assert		 		"printf notes | rexreplace foo bar my.file -P 2>&1 1>/dev/null"    'my.file '
+
+reset
+assert		 		"printf '' | rexreplace foo bar my.file 2>&1 1>/dev/null"    'my.file '
+
+reset
+assert		 		"printf '\n' | rexreplace foo bar my.file 2>&1 1>/dev/null"    'my.file '
+
+
+
 
 	
 
diff --git a/test/js/fix/719.test.js b/test/js/fix/719.test.js
new file mode 100644
index 00000000..4a93cec8
--- /dev/null
+++ b/test/js/fix/719.test.js
@@ -0,0 +1,130 @@
+// https://github.com/mathiasrw/rexreplace/issues/719
+// Warn when data is piped in and files are also given, but the piped data is not used.
+import {describe, test, expect} from 'bun:test';
+import fs from 'fs';
+import {rr} from '../helper.js';
+
+const warnMsg = ' 🟡 Data is piped in, but no flag tells what to do with it. It is not used.\n';
+
+describe('#719 warn when piped data is not used', () => {
+	test('warns when data is piped in and files are given', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: 'notes',
+		});
+		expect(result.err).toContain(warnMsg);
+		expect(result.exit).toBe(null);
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('warning starts with 🟡 and goes to stderr', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: 'notes',
+		});
+		expect(result.err.startsWith(' 🟡')).toBe(true);
+		expect(result.out).toBe('');
+	});
+
+	test('--quiet hides the warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: 'notes',
+			quiet: true,
+		});
+		expect(result.err).toBe('');
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('--quiet-total hides the warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: 'notes',
+			quietTotal: true,
+		});
+		expect(result.err).toBe('');
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('warning never stops the run, also not with --halt', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: 'notes',
+			halt: true,
+		});
+		expect(result.err).toContain(warnMsg);
+		expect(result.exit).toBe(null);
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('--void-pipe suppresses the warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: 'notes',
+			voidPipe: true,
+		});
+		expect(result.err).not.toContain(warnMsg);
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('--replacement-pipe suppresses the warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', '_', {
+			includeGlob: ['my.file'],
+			pipedData: 'bar',
+			replacementPipe: true,
+		});
+		expect(result.err).not.toContain(warnMsg);
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('--replacement-js suppresses the warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'pipe', {
+			includeGlob: ['my.file'],
+			pipedData: 'bar',
+			replacementJs: true,
+		});
+		expect(result.err).not.toContain(warnMsg);
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('barbar');
+	});
+
+	test('empty piped data does not trigger a warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const result = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: '',
+		});
+		expect(result.err).not.toContain(warnMsg);
+	});
+
+	test('piped data with only a newline does not trigger a warning', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		const resultN = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: '\n',
+		});
+		expect(resultN.err).not.toContain(warnMsg);
+
+		const resultRN = await rr('foo', 'bar', {
+			includeGlob: ['my.file'],
+			pipedData: '\r\n',
+		});
+		expect(resultRN.err).not.toContain(warnMsg);
+	});
+
+	test('piped data when no files are given does not trigger a warning', async () => {
+		const result = await rr('foo', 'bar', {
+			includeGlob: [],
+			pipedData: 'foobar',
+		});
+		expect(result.err).not.toContain(warnMsg);
+		expect(result.out).toBe('barbar');
+	});
+});