Userland: Implement tac command

Nobody care about tac :^).

Userland/Utilities/tac.cpp

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2021, Federico Guerinoni <guerinoni.federico@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Vector.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <unistd.h>
+
+void print_lines(const Vector<String>& vec);
+
+int main(int argc, char** argv)
+{
+    if (pledge("stdio rpath", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    const char* path = nullptr;
+    Core::ArgsParser args_parser;
+    args_parser.set_general_help("Concatenate files or pipes to stdout, last line first.");
+    args_parser.add_positional_argument(path, "File path", "path", Core::ArgsParser::Required::No);
+    args_parser.parse(argc, argv);
+
+    RefPtr<Core::File> file;
+    if (path == nullptr) {
+        file = Core::File::standard_input();
+    } else {
+        auto file_or_error = Core::File::open(path, Core::File::ReadOnly);
+        if (file_or_error.is_error()) {
+            warnln("Failed to open {}: {}", path, file_or_error.error());
+            return 1;
+        }
+        file = file_or_error.value();
+    }
+
+    Vector<String> lines;
+    while (file->can_read_line()) {
+        auto line = file->read_line();
+        lines.append(line);
+    }
+
+    for (int i = lines.size() - 1; i >= 0; --i)
+        outln("{}", lines[i]);
+
+    return 0;
+}