Added show non-printing option.

lib/dcat.dart

@@ -2,33 +2,35 @@
 // Use of this source code is governed by a BSD-style license that can be found
 // in the LICENSE file.
 
+/// Library to concatenate file(s) to standard output,
 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.
+/// Specify a [log] for debugging or testing purpose.
 Future<int> cat(List<String> paths,
-    {List<String>? log,
+    {String appName = '',
+    List<String>? log,
     bool showEnds = false,
     bool numberNonBlank = false,
     bool showLineNumbers = false,
     bool showTabs = false,
-    bool squeezeBlank = false}) async {
+    bool squeezeBlank = false,
+    bool showNonPrinting = 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);
+        numberNonBlank, showTabs, squeezeBlank, showNonPrinting);
   } else {
     for (final path in paths) {
       try {
@@ -40,8 +42,16 @@ Future<int> cat(List<String> paths,
               .bind(File(path).openRead())
               .transform(const LineSplitter());
         }
-        lineNumber = await _writeLines(lines, lineNumber, log, showEnds,
-            showLineNumbers, numberNonBlank, showTabs, squeezeBlank);
+        lineNumber = await _writeLines(
+            lines,
+            lineNumber,
+            log,
+            showEnds,
+            showLineNumbers,
+            numberNonBlank,
+            showTabs,
+            squeezeBlank,
+            showNonPrinting);
       } on FileSystemException catch (e) {
         final String? osMessage = e.osError?.message;
         final String message;
@@ -50,25 +60,63 @@ Future<int> cat(List<String> paths,
         } else {
           message = e.message;
         }
-        returnCode = await printError(message, path: path);
+        returnCode = await printError(message, appName: appName, path: path);
       } on FormatException {
-        returnCode = await printError('Binary file not supported.', path: path);
+        returnCode = await printError('Binary file not supported.',
+            appName: appName, path: path);
       } catch (e) {
-        returnCode = await printError(e.toString(), path: path);
+        returnCode =
+            await printError(e.toString(), appName: appName, path: path);
       }
     }
   }
   return returnCode;
 }
 
+/// Parses line with non-printing characters.
+Future<String> _parseNonPrinting(String line, bool showTabs) async {
+  final sb = StringBuffer();
+  for (var ch in line.runes) {
+    if (ch >= 32) {
+      if (ch < 127) {
+        sb.writeCharCode(ch);
+      } else if (ch == 127) {
+        sb.write('^?');
+      } else {
+        sb.write('M-');
+        if (ch >= 128 + 32) {
+          if (ch < 128 + 127) {
+            sb.writeCharCode(ch - 128);
+          } else {
+            sb.write('^?');
+          }
+        } else {
+          sb
+            ..write('^')
+            ..writeCharCode(ch - 128 + 64);
+        }
+      }
+    } else if (ch == 9 && !showTabs) {
+      sb.write('\t');
+    } else {
+      sb
+        ..write('^')
+        ..writeCharCode(ch + 64);
+    }
+  }
+  return sb.toString();
+}
+
 /// 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: $message');
+    {String appName = '', String path = ''}) async {
+  if (appName.isNotEmpty) {
+    stderr.write('$appName: ');
   }
+  if (path.isNotEmpty) {
+    stderr.write('$path: ');
+  }
+  stderr.writeln(message);
   return exitFailure;
 }
 
@@ -83,7 +131,8 @@ Future<int> _writeLines(Stream<String> lines, int lineNumber,
     bool showLineNumbers = false,
     bool showNonBlank = false,
     bool showTabs = false,
-    bool squeezeBlank = false]) async {
+    bool squeezeBlank = false,
+    bool showNonPrinting = false]) async {
   var emptyLine = 0;
   final sb = StringBuffer();
   await for (final line in lines) {
@@ -95,14 +144,18 @@ Future<int> _writeLines(Stream<String> lines, int lineNumber,
     } else {
       emptyLine = 0;
     }
-    if (showNonBlank || showLineNumbers) {
-      sb.write('${lineNumber++}: ');
+    if (showLineNumbers || (showNonBlank && line.isNotEmpty)) {
+      sb.write('${lineNumber++}  '.padLeft(8));
     }
-    if (showTabs) {
+
+    if (showNonPrinting) {
+      sb.write(await _parseNonPrinting(line, showTabs));
+    } else if (showTabs) {
       sb.write(line.replaceAll('\t', '^I'));
     } else {
       sb.write(line);
     }
+
     if (showEnds) {
       sb.write('\$');
     }