tac: Support concatenating multiple files (SerenityOS#6970)

Userland/Utilities/tac.cpp

@@ -8,40 +8,48 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <unistd.h>
-
 int main(int argc, char** argv)
 {
  if (pledge("stdio rpath", nullptr) < 0) {
  perror("pledge");
  return 1;
  }
 
- const char* path = nullptr;
+ Vector<String> paths;
+
  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.add_positional_argument(paths, "File path(s)", "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;
+ auto read_lines = [&](RefPtr<Core::File> file) {
+ Vector<String> lines;
+ while (file->can_read_line()) {
+ lines.append(file->read_line());
  }
- file = file_or_error.value();
- }
+ file->close();
+ for (int i = lines.size() - 1; i >= 0; --i)
+ outln("{}", lines[i]);
+ };
 
- Vector<String> lines;
- while (file->can_read_line()) {
- auto line = file->read_line();
- lines.append(line);
+ if (!paths.is_empty()) {
+ for (auto const& path : paths) {
+ RefPtr<Core::File> file;
+ if (path == "-") {
+ 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, strerror(errno));
+ continue;
+ }
+ file = file_or_error.release_value();
+ }
+ read_lines(file);
+ }
+ } else {
+ read_lines(Core::File::standard_input());
  }
 
- for (int i = lines.size() - 1; i >= 0; --i)
- outln("{}", lines[i]);
-
  return 0;
 }