Utilities: Add errno utility

Author: https://github.com/bcoles
Commit: https://github.com/SerenityOS/serenity/commit/a6ec0243529
Pull-request: https://github.com/SerenityOS/serenity/pull/7134
Reviewed-by: https://github.com/linusg

Userland/Utilities/errno.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <stdlib.h>
+
+int main(int argc, char** argv)
+{
+    bool list = false;
+    bool search = false;
+    const char* keyword = nullptr;
+
+    Core::ArgsParser args_parser;
+    args_parser.add_positional_argument(keyword, "Error number or string to search", "keyword", Core::ArgsParser::Required::No);
+    args_parser.add_option(list, "List all errno values", "list", 'l');
+    args_parser.add_option(search, "Search for error descriptions containing keyword", "search", 's');
+    args_parser.parse(argc, argv);
+
+    if (list) {
+        for (int i = 0; i < sys_nerr; i++) {
+            outln("{} {}", i, strerror(i));
+        }
+        return 0;
+    }
+
+    if (keyword == nullptr)
+        return 0;
+
+    if (search) {
+        for (int i = 0; i < sys_nerr; i++) {
+            auto error = String::formatted("{}", strerror(i));
+            if (error.contains(keyword, CaseSensitivity::CaseInsensitive)) {
+                outln("{} {}", i, error);
+            }
+        }
+        return 0;
+    }
+
+    auto maybe_errno = StringView { keyword }.to_int();
+    if (!maybe_errno.has_value()) {
+        warnln("ERROR: Not understood: {}", keyword);
+        return 1;
+    }
+
+    auto error = String::formatted("{}", strerror(maybe_errno.value()));
+    if (error == "Unknown error") {
+        warnln("ERROR: Unknown errno: {}", keyword);
+        return 1;
+    }
+    outln("{} {}", keyword, error);
+
+    return 0;
+}