Split into library.

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;
+}