cmp: Implement cmp(1)

2 files changed, 102 insertions, 0 deletions

diff --git a/Userland/Utilities/CMakeLists.txt b/Userland/Utilities/CMakeLists.txt
index d9582b6eac..afad68607d 100644
--- a/Userland/Utilities/CMakeLists.txt
+++ b/Userland/Utilities/CMakeLists.txt
@@ -71,6 +71,7 @@ target_link_libraries(chown LibMain)
 target_link_libraries(chres LibGUI LibMain)
 target_link_libraries(cksum LibCrypto LibMain)
 target_link_libraries(clear LibMain)
+target_link_libraries(cmp LibMain)
 target_link_libraries(comm LibMain)
 target_link_libraries(config LibConfig LibMain)
 target_link_libraries(copy LibGUI LibMain)
diff --git a/Userland/Utilities/cmp.cpp b/Userland/Utilities/cmp.cpp
new file mode 100644
index 0000000000..01374164de
--- /dev/null
+++ b/Userland/Utilities/cmp.cpp
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/Stream.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <unistd.h>
+
+static ErrorOr<NonnullOwnPtr<Core::Stream::BufferedFile>> open_file_or_stdin(String const& filename)
+{
+    OwnPtr<Core::Stream::File> file;
+    if (filename == "-") {
+        file = TRY(Core::Stream::File::adopt_fd(STDIN_FILENO, Core::Stream::OpenMode::Read));
+    } else {
+        file = TRY(Core::Stream::File::open(filename, Core::Stream::OpenMode::Read));
+    }
+    return TRY(Core::Stream::BufferedFile::create(file.release_nonnull()));
+}
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    Main::set_return_code_for_errors(2);
+    TRY(Core::System::pledge("stdio rpath"));
+
+    Core::ArgsParser parser;
+    String filename1;
+    String filename2;
+    bool verbose = false;
+    bool silent = false;
+
+    parser.set_general_help("Compare two files, and report the first byte that does not match. Returns 0 if files are identical, or 1 if they differ.");
+    parser.add_positional_argument(filename1, "First file to compare", "file1", Core::ArgsParser::Required::Yes);
+    parser.add_positional_argument(filename2, "Second file to compare", "file2", Core::ArgsParser::Required::Yes);
+    parser.add_option(verbose, "Output every byte mismatch, not just the first", "verbose", 'l');
+    parser.add_option(silent, "Disable all output", "silent", 's');
+    parser.parse(arguments);
+
+    // When opening STDIN as both files, the results are undefined.
+    // Let's just report that it matches.
+    if (filename1 == "-" && filename2 == "-")
+        return 0;
+
+    auto file1 = TRY(open_file_or_stdin(filename1));
+    auto file2 = TRY(open_file_or_stdin(filename2));
+    TRY(Core::System::unveil(nullptr, nullptr));
+
+    int line_number = 1;
+    int byte_number = 1;
+    Array<u8, 1> buffer1;
+    Array<u8, 1> buffer2;
+    bool files_match = true;
+
+    auto report_mismatch = [&]() {
+        files_match = false;
+        if (silent)
+            return;
+        if (verbose)
+            outln("{} {:o} {:o}", byte_number, buffer1[0], buffer2[0]);
+        else
+            outln("{} {} differ: char {}, line {}", filename1, filename2, byte_number, line_number);
+    };
+
+    auto report_eof = [&](auto& shorter_file_name) {
+        files_match = false;
+        if (silent)
+            return;
+        auto additional_info = verbose
+            ? String::formatted(" after byte {}", byte_number)
+            : String::formatted(" after byte {}, line {}", byte_number, line_number);
+        warnln("cmp: EOF on {}{}", shorter_file_name, additional_info);
+    };
+
+    while (true) {
+        TRY(file1->read(buffer1));
+        TRY(file2->read(buffer2));
+
+        if (file1->is_eof() && file2->is_eof())
+            break;
+
+        if (file1->is_eof() || file2->is_eof()) {
+            report_eof(file1->is_eof() ? filename1 : filename2);
+            break;
+        }
+
+        if (buffer1[0] != buffer2[0]) {
+            report_mismatch();
+            if (!verbose)
+                break;
+        }
+
+        if (buffer1[0] == '\n')
+            ++line_number;
+        ++byte_number;
+    }
+
+    return files_match ? 0 : 1;
+}