Enhancing cat Utility (Add -n, -v, -b, and -E flags to cat)

Makefile

@@ -116,6 +116,7 @@ mkfs/mkfs: mkfs/mkfs.c $K/fs.h $K/param.h
 .PRECIOUS: %.o
 
 UPROGS=\
+	$U/_test\
 	$U/_cat\
 	$U/_echo\
 	$U/_forktest\

user/cat.c

@@ -4,39 +4,136 @@
 
 char buf[512];
 
-void
-cat(int fd)
-{
+//flag variables
+uint8 nflag = 0;
+uint8 vflag = 0;
+uint8 bflag = 0;
+uint8 Eflag = 0;
+
+/**
+ * @cat Display file content with various flags.
+ *
+ * This function reads the content of a file descriptor and displays it
+ * according to the specified flags. It supports line numbering, showing
+ * non-printing characters, numbering non-blank lines, and displaying
+ * end-of-line markers.
+ *
+ * @param fd The file descriptor to read from.
+ * @param line_numbering If non-zero, number all output lines.
+ * @param show_non_printing If non-zero, show non-printing characters in caret notation.
+ * @param number_non_blank If non-zero, number only non-blank lines.
+ * @param show_end_of_line If non-zero, display '$' at the end of each line.
+ */
+
+void cat(int fd, int line_numbering, int show_non_printing, int number_non_blank, int show_end_of_line) {
   int n;
+  int line_number = 1;
+  int i;
+  int is_blank_line = 1;
 
-  while((n = read(fd, buf, sizeof(buf))) > 0) {
-    if (write(1, buf, n) != n) {
-      fprintf(2, "cat: write error\n");
-      exit(1);
+  //read the file content in chunks
+  while ((n = read(fd, buf, sizeof(buf))) > 0) {
+    for (i = 0; i < n; i++) {
+      //check if the current character is part of a blank line
+      if (buf[i] != '\n' && buf[i] != '\r' && buf[i] != '\t' && buf[i] != ' ') {
+        is_blank_line = 0;
+      }
+
+      //add line numbers if the -n or -b flag is set
+      if ((line_numbering || (number_non_blank && !is_blank_line)) && (i == 0 || buf[i-1] == '\n')) {
+        printf("%6d  ", line_number++);
+      }
+
+      //convert non-printing characters to a visible format if the -v flag is set
+      //tested externally with test.c amd ran with OS as test (user program)
+      if (show_non_printing && (buf[i] < 32 || buf[i] == 127)) {
+        if (buf[i] == 127) {
+          printf("^?");
+        } else {
+          printf("^%c", buf[i] + 64);
+        }
+      } else {
+        //write the character to the output
+        if (write(1, &buf[i], 1) != 1) {
+          fprintf(2, "cat: write error\n");
+          exit(1);
+        }
+      }
+
+      //display $ at the end of each line if the -E flag is set
+      if (show_end_of_line && buf[i] == '\n') {
+        if (!number_non_blank || !is_blank_line) {
+          printf("$");
+        }
+      }
+
+      //reset blank line flag at the end of each line
+      if (buf[i] == '\n') {
+        is_blank_line = 1;
+      }
     }
   }
-  if(n < 0){
+
+  //handle read errors (unchanged)
+  if (n < 0) {
     fprintf(2, "cat: read error\n");
     exit(1);
   }
 }
 
-int
-main(int argc, char *argv[])
-{
+int main(int argc, char *argv[]) {
   int fd, i;
+  int line_numbering = 0;
+  int show_non_printing = 0;
+  int number_non_blank = 0;
+  int show_end_of_line = 0;
+
+  //parse command-line arguments for flags
+  for (i = 1; i < argc; i++) {
+    if (argv[i][0] == '-') {
+      for (int j = 1; argv[i][j] != '\0'; j++) { //allows handling multiple flags in a single argument
+        switch (argv[i][j]) {
+          case 'n':
+            nflag = 1;
+            break;
+          case 'v':
+            vflag = 1;
+            break;
+          case 'b':
+            bflag = 1;
+            break;
+          case 'E':
+            Eflag = 1;
+            break;
+          default:
+            fprintf(2, "Unrecognized flag: -%c\n", argv[i][j]);
+            exit(1);
+        }
+      }
+    } else {
+      break;
+    }
+  }
+
+  //set the flag variables
+  line_numbering = nflag;
+  show_non_printing = vflag;
+  number_non_blank = bflag;
+  show_end_of_line = Eflag;
 
-  if(argc <= 1){
-    cat(0);
+  //if no files are specified, read from standard input
+  if (i == argc) {
+    cat(0, line_numbering, show_non_printing, number_non_blank, show_end_of_line);
     exit(0);
   }
 
-  for(i = 1; i < argc; i++){
-    if((fd = open(argv[i], 0)) < 0){
+  //process each file specified in the command-line arguments (unchanged, except for, for and cat args)
+  for (; i < argc; i++) {
+    if ((fd = open(argv[i], 0)) < 0) {
       fprintf(2, "cat: cannot open %s\n", argv[i]);
       exit(1);
     }
-    cat(fd);
+    cat(fd, line_numbering, show_non_printing, number_non_blank, show_end_of_line);
     close(fd);
   }
   exit(0);

user/test.c

@@ -0,0 +1,47 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+
+
+//function to convert non-printing characters to caret notation
+//same function as the -v flag, to test
+void print_with_caret_notation(const char *str) {
+  for (int i = 0; i < strlen(str); i++) {
+    if (str[i] < 32 || str[i] == 127) {
+      if (str[i] == 127) {
+        printf("^?");
+      } else {
+        printf("^%c", str[i] + 64);
+      }
+    } else {
+      printf("%c", str[i]);
+    }
+  }
+  printf("\n");
+}
+
+int main() {
+  //test cases with non-printing characters
+  const char *test1 = "Hello\001World"; // SOH (ASCII 1)
+  const char *test2 = "Tab\tCharacter"; // TAB (ASCII 9)
+  const char *test3 = "New\nLine";      // LF (ASCII 10)
+  const char *test4 = "Carriage\rReturn"; // CR (ASCII 13)
+  const char *test5 = "Delete\177Char"; // DEL (ASCII 127)
+
+  printf("Test 1: ");
+  print_with_caret_notation(test1);
+
+  printf("Test 2: ");
+  print_with_caret_notation(test2);
+
+  printf("Test 3: ");
+  print_with_caret_notation(test3);
+
+  printf("Test 4: ");
+  print_with_caret_notation(test4);
+
+  printf("Test 5: ");
+  print_with_caret_notation(test5);
+
+  return 0;
+}

user/test.txt

@@ -0,0 +1,13 @@
+Hello, World!
+This is a test file.
+
+It contains some non-printing characters.
+Here is a tab:	<- tab character
+Here is a newline:
+
+Here is a carriage return:
+<- carriage return character
+Here is a bell character:<- bell character
+Here is a delete character:<- delete character
+Here is a form feed character:<- form feed character
+Here is a vertical tab character:<- vertical tab character