diff --git a/bin/dcat.dart b/bin/dcat.dart
index 3072f56..7025cc6 100644
--- a/bin/dcat.dart
+++ b/bin/dcat.dart
@@ -1,16 +1,15 @@
 // Copyright (c) 2021, Erik C. Thauvin. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be found
 // in the LICENSE file.
-import 'dart:convert';
+
 import 'dart:io';
 
 import 'package:args/args.dart';
+import 'package:dcat/dcat.dart';
 import 'package:indent/indent.dart';
 
-const appName = 'dcat';
+const appName = libName;
 const appVersion = '1.0.0';
-const exitFailure = 1;
-const exitSuccess = 0;
 const helpFlag = 'help';
 const nonBlankFlag = 'number-nonblank';
 const numberFlag = 'number';
@@ -19,69 +18,9 @@ const showTabsFlag = 'show-tabs';
 const squeezeBlank = 'squeeze-blank';
 const versionFlag = 'version';
 
-/// Prints [message] and [path] to stderr.
-Future<int> handleError(String message, {String path = ''}) async {
-  if (path.isNotEmpty) {
-    stderr.writeln('$appName: $path: $message');
-  } else {
-    stderr.write('$appName: $message');
-  }
-  return exitFailure;
-}
-
-/// Concatenates files in [paths].
-Future<int> cat(List<String> paths,
-    {List<String>? log,
-    bool showEnds = false,
-    bool numberNonBlank = false,
-    bool showLineNumbers = false,
-    bool showTabs = false,
-    bool squeezeBlank = false}) async {
-  var lineNumber = 1;
-  var returnCode = 0;
-  log?.clear();
-  if (paths.isEmpty) {
-    final lines = await _readStdin();
-    await _writeLines(lines, lineNumber, log, showEnds, showLineNumbers,
-        numberNonBlank, showTabs, squeezeBlank);
-  } else {
-    for (final path in paths) {
-      try {
-        final Stream<String> lines;
-        if (path == '-') {
-          lines = await _readStdin();
-        } else {
-          lines = utf8.decoder
-              .bind(File(path).openRead())
-              .transform(const LineSplitter());
-        }
-        lineNumber = await _writeLines(lines, lineNumber, log, showEnds,
-            showLineNumbers, numberNonBlank, showTabs, squeezeBlank);
-      } on FileSystemException catch (e) {
-        final String? osMessage = e.osError?.message;
-        final String message;
-        if (osMessage != null && osMessage.isNotEmpty) {
-          message = osMessage;
-        } else {
-          message = e.message;
-        }
-        returnCode = await handleError(message, path: path);
-      } on FormatException {
-        returnCode =
-            await handleError('Binary file not supported.', path: path);
-      } catch (e) {
-        returnCode = await handleError(e.toString(), path: path);
-      }
-    }
-  }
-  return returnCode;
-}
-
 /// Concatenates files specified in [arguments].
 ///
-/// ```
-/// dcat [OPTION]... [FILE]...
-/// ```
+/// Usage: `dcat [OPTION]... [FILE]...`
 Future<int> main(List<String> arguments) async {
   final parser = ArgParser();
   Future<int> returnCode;
@@ -109,8 +48,9 @@ Future<int> main(List<String> arguments) async {
   try {
     argResults = parser.parse(arguments);
   } on FormatException catch (e) {
-    return await handleError(
-        "${e.message}\nTry '$appName --$helpFlag' for more information.");
+    return await printError(
+        "${e.message}\nTry '$appName --$helpFlag' for more information.",
+        appName: appName);
   }
 
   if (argResults[helpFlag]) {
@@ -131,21 +71,17 @@ Future<int> main(List<String> arguments) async {
   return exitCode;
 }
 
-/// Prints version info.
+/// Prints the version info.
 Future<int> printVersion() async {
   print('''$appName (Dart cat) $appVersion
 Copyright (C) 2021 Erik C. Thauvin
 License: 3-Clause BSD <https://opensource.org/licenses/BSD-3-Clause>
  
-Based on <https://dart.dev/tutorials/server/cmdline>
+Inspired by <https://dart.dev/tutorials/server/cmdline>
 Written by Erik C. Thauvin <https://erik.thauvin.net/>''');
   return exitSuccess;
 }
 
-/// Reads from stdin.
-Future<Stream<String>> _readStdin() async =>
-    stdin.transform(utf8.decoder).transform(const LineSplitter());
-
 /// Prints usage with [options].
 Future<int> usage(String options) async {
   print('''Usage: $appName [OPTION]... [FILE]...
@@ -161,40 +97,3 @@ Examples:
  Source and documentation: <https://github.com/ethauvin/dcat>''');
   return exitSuccess;
 }
-
-/// Writes lines to stdout.
-Future<int> _writeLines(Stream<String> lines, int lineNumber,
-    [List<String>? log,
-    bool showEnds = false,
-    bool showLineNumbers = false,
-    bool showNonBlank = false,
-    bool showTabs = false,
-    bool sqeezeBlank = false]) async {
-  var emptyLine = 0;
-  final sb = StringBuffer();
-  await for (final line in lines) {
-    sb.clear();
-    if (sqeezeBlank && line.isEmpty) {
-      if (++emptyLine >= 2) {
-        continue;
-      }
-    } else {
-      emptyLine = 0;
-    }
-    if (showNonBlank || showLineNumbers) {
-      sb.write('${lineNumber++}: ');
-    }
-    if (showTabs) {
-      sb.write(line.replaceAll('\t', '^I'));
-    } else {
-      sb.write(line);
-    }
-    if (showEnds) {
-      sb.write('\$');
-    }
-
-    log?.add(sb.toString());
-    stdout.writeln(sb);
-  }
-  return lineNumber;
-}
diff --git a/lib/dcat.dart b/lib/dcat.dart
new file mode 100644
index 0000000..0313ace
--- /dev/null
+++ b/lib/dcat.dart
@@ -0,0 +1,114 @@
+// Copyright (c) 2021, Erik C. Thauvin. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be found
+// in the LICENSE file.
+
+library dcat;
+
+import 'dart:convert';
+import 'dart:io';
+
+const libName = 'dcat';
+const exitFailure = 1;
+const exitSuccess = 0;
+
+/// Concatenates files in [paths] to [stdout]
+///
+/// The parameters are similar to the [GNU cat utility](https://www.gnu.org/software/coreutils/manual/html_node/cat-invocation.html#cat-invocation).
+/// Specify a [log] for debugging purpose.
+Future<int> cat(List<String> paths,
+    {List<String>? log,
+    bool showEnds = false,
+    bool numberNonBlank = false,
+    bool showLineNumbers = false,
+    bool showTabs = false,
+    bool squeezeBlank = false}) async {
+  var lineNumber = 1;
+  var returnCode = 0;
+  log?.clear();
+  if (paths.isEmpty) {
+    final lines = await _readStdin();
+    await _writeLines(lines, lineNumber, log, showEnds, showLineNumbers,
+        numberNonBlank, showTabs, squeezeBlank);
+  } else {
+    for (final path in paths) {
+      try {
+        final Stream<String> lines;
+        if (path == '-') {
+          lines = await _readStdin();
+        } else {
+          lines = utf8.decoder
+              .bind(File(path).openRead())
+              .transform(const LineSplitter());
+        }
+        lineNumber = await _writeLines(lines, lineNumber, log, showEnds,
+            showLineNumbers, numberNonBlank, showTabs, squeezeBlank);
+      } on FileSystemException catch (e) {
+        final String? osMessage = e.osError?.message;
+        final String message;
+        if (osMessage != null && osMessage.isNotEmpty) {
+          message = osMessage;
+        } else {
+          message = e.message;
+        }
+        returnCode = await printError(message, path: path);
+      } on FormatException {
+        returnCode = await printError('Binary file not supported.', path: path);
+      } catch (e) {
+        returnCode = await printError(e.toString(), path: path);
+      }
+    }
+  }
+  return returnCode;
+}
+
+/// Prints the [appName], [path] and error [message] to [stderr].
+Future<int> printError(String message,
+    {String appName = libName, String path = ''}) async {
+  if (path.isNotEmpty) {
+    stderr.writeln('$libName: $path: $message');
+  } else {
+    stderr.write('$libName: $message');
+  }
+  return exitFailure;
+}
+
+/// Reads from stdin.
+Future<Stream<String>> _readStdin() async =>
+    stdin.transform(utf8.decoder).transform(const LineSplitter());
+
+/// Writes lines to stdout.
+Future<int> _writeLines(Stream<String> lines, int lineNumber,
+    [List<String>? log,
+    bool showEnds = false,
+    bool showLineNumbers = false,
+    bool showNonBlank = false,
+    bool showTabs = false,
+    bool squeezeBlank = false]) async {
+  var emptyLine = 0;
+  final sb = StringBuffer();
+  await for (final line in lines) {
+    sb.clear();
+    if (squeezeBlank && line.isEmpty) {
+      if (++emptyLine >= 2) {
+        continue;
+      }
+    } else {
+      emptyLine = 0;
+    }
+    if (showNonBlank || showLineNumbers) {
+      sb.write('${lineNumber++}: ');
+    }
+    if (showTabs) {
+      sb.write(line.replaceAll('\t', '^I'));
+    } else {
+      sb.write(line);
+    }
+    if (showEnds) {
+      sb.write('\$');
+    }
+
+    log?.add(sb.toString());
+    stdout.writeln(sb);
+  }
+  return lineNumber;
+}
diff --git a/test/dcat_test.dart b/test/dcat_test.dart
index b6b6559..74fb8d6 100644
--- a/test/dcat_test.dart
+++ b/test/dcat_test.dart
@@ -1,46 +1,46 @@
+import 'package:dcat/dcat.dart';
 import 'package:test/test.dart';
 
-import '../bin/dcat.dart' as dcat;
+import '../bin/dcat.dart' as app;
 
 void main() {
   final List<String> log = [];
   int exitCode;
 
   test('Test Help', () async {
-    expect(dcat.main(['-h']), completion(equals(0)));
-    expect(dcat.main(['--help']), completion(equals(0)));
-    exitCode = await dcat.main(['-h']);
-    expect(exitCode, equals(dcat.exitSuccess));
+    expect(app.main(['-h']), completion(equals(0)));
+    expect(app.main(['--help']), completion(equals(0)));
+    exitCode = await app.main(['-h']);
+    expect(exitCode, equals(exitSuccess));
   });
 
   test('Test --version', () async {
-    expect(dcat.main(['--version']), completion(equals(0)));
-    exitCode = await dcat.main(['--version']);
-    expect(exitCode, equals(dcat.exitSuccess));
+    expect(app.main(['--version']), completion(equals(0)));
+    exitCode = await app.main(['--version']);
+    expect(exitCode, equals(exitSuccess));
   });
 
   test('Test directory', () async {
-    exitCode = await dcat.main(['bin']);
-    expect(exitCode, equals(dcat.exitFailure));
+    exitCode = await app.main(['bin']);
+    expect(exitCode, equals(exitFailure));
   });
 
   test('Test missing file', () async {
-    exitCode = await dcat.main(['foo']);
-    expect(exitCode, equals(dcat.exitFailure), reason: 'foo not found');
-    exitCode = await dcat.main(['bin/dcat.dart', 'foo']);
-    expect(exitCode, equals(dcat.exitFailure), reason: 'one missing file');
+    exitCode = await app.main(['foo']);
+    expect(exitCode, equals(exitFailure), reason: 'foo not found');
+    exitCode = await app.main(['bin/dcat.dart', 'foo']);
+    expect(exitCode, equals(exitFailure), reason: 'one missing file');
   });
 
   test('Test cat source', () async {
-    await dcat.cat(['bin/dcat.dart'], log: log);
+    await cat(['bin/dcat.dart'], log: log);
     expect(log.isEmpty, false, reason: 'log is empty');
     expect(log.first, startsWith('// Copyright (c)'), reason: 'has copyright');
     expect(log.last, equals('}'));
   });
 
   test('Test cat -n source', () async {
-    exitCode =
-        await dcat.cat(['bin/dcat.dart'], log: log, showLineNumbers: true);
+    exitCode = await cat(['bin/dcat.dart'], log: log, showLineNumbers: true);
     expect(exitCode, 0, reason: 'result code is 0');
     expect(log.first, startsWith('1: // Copyright (c)'),
         reason: 'has copyright');
@@ -51,7 +51,7 @@ void main() {
   });
 
   test('Test cat -E', () async {
-    await dcat.cat(['test/test.txt'], log: log, showEnds: true);
+    await cat(['test/test.txt'], log: log, showEnds: true);
     var hasBlank = false;
     for (final String line in log) {
       expect(line, endsWith('\$'));
@@ -63,8 +63,8 @@ void main() {
   });
 
   test('Test cat -bE', () async {
-    await dcat
-        .cat(['test/test.txt'], log: log, numberNonBlank: true, showEnds: true);
+    await cat(['test/test.txt'],
+        log: log, numberNonBlank: true, showEnds: true);
     var hasBlank = false;
     for (final String line in log) {
       expect(line, endsWith('\$'));
@@ -76,7 +76,7 @@ void main() {
   });
 
   test('Test cat -T', () async {
-    await dcat.cat(['test/test.txt'], log: log, showTabs: true);
+    await cat(['test/test.txt'], log: log, showTabs: true);
     var hasTab = false;
     for (final String line in log) {
       if (line.startsWith('^I')) {
@@ -88,7 +88,7 @@ void main() {
   });
 
   test('Test cat -s', () async {
-    await dcat.cat(['test/test.txt'], log: log, squeezeBlank: true);
+    await cat(['test/test.txt'], log: log, squeezeBlank: true);
     var hasSqueeze = true;
     var prevLine = 'foo';
     for (final String line in log) {