Utilities: Add support for -d flag to tr

Author: https://github.com/boricj
Commit: https://github.com/SerenityOS/serenity/commit/897a7060757
Pull-request: https://github.com/SerenityOS/serenity/pull/8567
Reviewed-by: https://github.com/MaxWipfli ✅
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/gunnarbeutner

Userland/Utilities/tr.cpp

@@ -12,26 +12,45 @@
 
 int main(int argc, char** argv)
 {
+    bool delete_flag = false;
     const char* from_chars = nullptr;
     const char* to_chars = nullptr;
 
     Core::ArgsParser args_parser;
+    args_parser.add_option(delete_flag, "Delete characters instead of replacing", nullptr, 'd');
     args_parser.add_positional_argument(from_chars, "Character to translate from", "from");
-    args_parser.add_positional_argument(to_chars, "Character to translate to", "to");
+    args_parser.add_positional_argument(to_chars, "Character to translate to", "to", Core::ArgsParser::Required::No);
     args_parser.parse(argc, argv);
 
-    // TODO: Support multiple characters to translate from and to
-    auto from = from_chars[0];
-    auto to = to_chars[0];
+    if (!to_chars && !delete_flag) {
+        args_parser.print_usage(stderr, argv[0]);
+        return 1;
+    }
 
-    for (;;) {
-        char ch = fgetc(stdin);
-        if (feof(stdin))
-            break;
-        if (ch == from)
-            putchar(to);
-        else
-            putchar(ch);
+    if (delete_flag) {
+        auto from_str = AK::StringView(from_chars);
+
+        for (;;) {
+            char ch = fgetc(stdin);
+            if (feof(stdin))
+                break;
+            if (!from_str.contains(ch))
+                putchar(ch);
+        }
+    } else {
+        // TODO: Support multiple characters to translate from and to
+        auto from = from_chars[0];
+        auto to = to_chars[0];
+
+        for (;;) {
+            char ch = fgetc(stdin);
+            if (feof(stdin))
+                break;
+            if (ch == from)
+                putchar(to);
+            else
+                putchar(ch);
+        }
     }
 
     return 0;