CatCommand with support for common flags

- Concatenates and displays file contents, mimicking Unix's cat utility.
- Handles flags -n (number all lines), -b (number non-blank lines), -e (display end-of-line characters), and -r (replace multiple empty lines).
- Supports multiple file arguments and flag combinations. Included cross-platform path normalization.

Author: siddhant-vij

src/com/unixtools/command/filecontent/CatCommand.java

@@ -1,5 +1,110 @@
 package com.unixtools.command.filecontent;
 
-public class CatCommand {
-  
+import com.unixtools.core.Command;
+
+import java.io.*;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+
+public class CatCommand implements Command {
+  private static final String VALID_FLAGS = "nber";
+  private boolean numberLines = false;
+  private boolean numberNonBlankLines = false;
+  private boolean showEndOfLine = false;
+  private boolean replaceMultipleEmptyLines = false;
+
+  @Override
+  public void execute(String[] args) {
+    List<String> flags = new ArrayList<>();
+    List<String> filePaths = new ArrayList<>();
+    parseArguments(args, flags, filePaths);
+
+    if (!areFlagsValid(flags)) {
+      System.out.println("Invalid flags. Valid flags are: " + VALID_FLAGS);
+      return;
+    }
+
+    for (String filePath : filePaths) {
+      readFileContents(normalizePath(filePath));
+    }
+  }
+
+  private void parseArguments(String[] args, List<String> flags, List<String> paths) {
+    for (String arg : args) {
+      if (arg.startsWith("-")) {
+        for (char flag : arg.substring(1).toCharArray()) {
+          switch (flag) {
+            case 'n':
+              numberLines = true;
+              break;
+            case 'b':
+              numberNonBlankLines = true;
+              break;
+            case 'e':
+              showEndOfLine = true;
+              break;
+            case 'r':
+              replaceMultipleEmptyLines = true;
+              break;
+            default:
+              flags.add(String.valueOf(flag));
+              break;
+          }
+        }
+      } else {
+        paths.add(arg);
+      }
+    }
+  }
+
+  private boolean areFlagsValid(List<String> flags) {
+    for (String flag : flags) {
+      if (!VALID_FLAGS.contains(flag)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private void readFileContents(String filePath) {
+    try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
+      String line;
+      int lineNumber = 0;
+      boolean lastLineEmpty = false;
+
+      while ((line = reader.readLine()) != null) {
+        boolean isLineEmpty = line.trim().isEmpty();
+
+        if (replaceMultipleEmptyLines && isLineEmpty) {
+          if (lastLineEmpty)
+            continue;
+          lastLineEmpty = true;
+        } else {
+          lastLineEmpty = false;
+        }
+
+        if (numberLines) {
+          System.out.printf("%6d  ", ++lineNumber);
+        } else if (numberNonBlankLines && !isLineEmpty) {
+          System.out.printf("%6d  ", ++lineNumber);
+        }
+
+        System.out.print(line);
+        if (showEndOfLine) {
+          System.out.print("$");
+        }
+        System.out.println();
+      }
+    } catch (IOException e) {
+      System.out.println("Error reading file: " + e.getMessage());
+    }
+  }
+
+  private String normalizePath(String path) {
+    String normalizedPath = path.replace("\\", "/");
+    Path pathObj = Paths.get(normalizedPath).normalize();
+    return pathObj.toString();
+  }
 }

src/com/unixtools/core/CommandFactory.java

@@ -50,6 +50,8 @@ public static Command getCommand(String commandName) {
        */
       case "echo":
         return new EchoCommand();
+      case "cat":
+        return new CatCommand();
       default:
         return null;
     }