feat(cat): refactor Python implementation for streaming and correctness

- Replace read-all-then-process with line-by-line streaming
- Fix -b flag: only skip truly empty lines (not whitespace-only lines)
- Fix line numbering: use tabs after number to match real cat format
- Maintain line number across multiple files for -n and -b flags
- Improve error handling with file-specific error messages

Author: Iswanna

implement-shell-tools/cat/cat.py

@@ -2,53 +2,41 @@
 import argparse
 
 def read_and_output_files():
-    # 1. Setup Argument Parser (Equivalent to 'commander')
+    # Setup Argument Parser (Equivalent to 'commander')
     parser = argparse.ArgumentParser(description="Python implementation of a basic cat-like utility")
     parser.add_argument("-n", "--number", action="store_true", help="number all output lines")
     parser.add_argument("-b", "--number-nonblank", action="store_true", help="number only non-empty lines")
     parser.add_argument("files", nargs="+", help="files to read")
 
     args = parser.parse_args()
 
-    try:
-        # 2. Read all file contents (Equivalent to Promise.all / fs.readFile)
-        file_contents = []
-        for file_path in args.files:
-            with open(file_path, "r", encoding="utf-8") as f:
-                file_contents.append(f.read())
-        
-        concatenated_content = "".join(file_contents)
-
-        # 3. Process Logic
-        if args.number:
-            # -n logic: number all lines
-            lines = concatenated_content.split("\n")
-            output = []
-            for index, line in enumerate(lines, start=1):
-                # rjust(6) is equivalent to padStart(6)
-                output.append(f"{str(index).rjust(6)}  {line}")
-            sys.stdout.write("\n".join(output))
-
-        elif args.number_nonblank:
-            # -b logic: number only non-empty lines
-            lines = concatenated_content.split("\n")
-            output = []
-            nonblank_line_number = 0
-            for line in lines:
-                if line.strip() == "":
-                    output.append(line)
-                else:
-                    nonblank_line_number += 1
-                    output.append(f"{str(nonblank_line_number).rjust(6)}  {line}")
-            sys.stdout.write("\n".join(output))
+    line_number = 1
 
-        else:
-            # No flags: standard output
-            sys.stdout.write(concatenated_content)
-
-    except Exception as err:
-        print(f"Error reading multiple files: {err}", file=sys.stderr)
-        sys.exit(1)
+    for file_path in args.files:
+        try:
+            with open(file_path, "r", encoding="utf-8") as f:
+                for line in f:
+                    # 1. Handle -b logic (number only non-blank lines)
+                    if args.number_nonblank:
+                        # A truly blank line is JUST a newline character (\n or \r\n)
+                        if line == "\n" or line == "\r\n":
+                            sys.stdout.write(line)
+                        else:
+                            # Standard cat uses a tab (\t) after the line number
+                            sys.stdout.write(f"{str(line_number).rjust(6)}\t{line}")
+                            line_number += 1
+
+                    # 2. Handle -n logic (number all lines)
+                    elif args.number:
+                        sys.stdout.write(f"{str(line_number).rjust(6)}\t{line}")
+                        line_number += 1
+
+                    # 3. Handle standard output
+                    else:
+                        sys.stdout.write(line)
+                        
+        except Exception as err:
+            print(f"cat: {file_path}: {err}", file=sys.stderr)
 
 if __name__ == "__main__":
-    read_and_output_files()
+    read_and_output_files()