2 files changed, 104 insertions, 0 deletions
diff --git a/Userland/Utilities/CMakeLists.txt b/Userland/Utilities/CMakeLists.txt
index 52e67a629d..3cf14b4a39 100644
--- a/Userland/Utilities/CMakeLists.txt
+++ b/Userland/Utilities/CMakeLists.txt
@@ -112,6 +112,7 @@ target_link_libraries(pkill PRIVATE LibRegex)
 target_link_libraries(pls PRIVATE LibCrypt)
 target_link_libraries(pro PRIVATE LibProtocol LibHTTP)
 target_link_libraries(run-tests PRIVATE LibRegex LibCoredump LibDebug)
+target_link_libraries(sed PRIVATE LibRegex)
 target_link_libraries(shot PRIVATE LibGfx LibGUI LibIPC)
 target_link_libraries(sql PRIVATE LibLine LibSQL LibIPC)
 target_link_libraries(su PRIVATE LibCrypt)
diff --git a/Userland/Utilities/sed.cpp b/Userland/Utilities/sed.cpp
new file mode 100644
index 0000000000..ebb814bd52
--- /dev/null
+++ b/Userland/Utilities/sed.cpp
@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2022, Eli Youngs <eli.m.youngs@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/GenericLexer.h>
+#include <AK/Vector.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/Stream.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <LibRegex/RegexMatcher.h>
+#include <LibRegex/RegexOptions.h>
+
+struct SubstitutionCommand {
+    Regex<PosixExtended> regex;
+    StringView replacement;
+    PosixOptions options;
+};
+
+static ErrorOr<SubstitutionCommand> parse_command(StringView command)
+{
+    auto generic_error_message = "Incomplete substitution command"sv;
+
+    auto lexer = GenericLexer(command);
+
+    auto address = lexer.consume_until('s');
+    if (!address.is_empty())
+        warnln("sed: Addresses are currently ignored");
+
+    if (!lexer.consume_specific('s'))
+        return Error::from_string_view(generic_error_message);
+
+    if (lexer.is_eof())
+        return Error::from_string_view(generic_error_message);
+
+    auto delimiter = lexer.consume();
+    if (delimiter == '\n' || delimiter == '\\')
+        return Error::from_string_literal("\\n and \\ cannot be used as delimiters.");
+
+    auto pattern = lexer.consume_until(delimiter);
+    if (pattern.is_empty())
+        return Error::from_string_literal("Substitution patterns cannot be empty.");
+
+    if (!lexer.consume_specific(delimiter))
+        return Error::from_string_view(generic_error_message);
+
+    auto replacement = lexer.consume_until(delimiter);
+
+    // According to Posix, "s/x/y" is an invalid substitution command.
+    // It must have a closing delimiter: "s/x/y/"
+    if (!lexer.consume_specific(delimiter))
+        return Error::from_string_literal("The substitution command was not properly terminated.");
+
+    PosixOptions const options = PosixOptions(PosixFlags::Global | PosixFlags::SingleMatch);
+
+    auto flags = lexer.consume_all();
+    if (!flags.is_empty())
+        warnln("sed: Flags are currently ignored");
+
+    return SubstitutionCommand { Regex<PosixExtended> { pattern }, replacement, options };
+}
+
+ErrorOr<int> serenity_main(Main::Arguments args)
+{
+    TRY(Core::System::pledge("stdio rpath"));
+
+    Core::ArgsParser args_parser;
+
+    StringView command_input;
+    Vector<StringView> filepaths;
+
+    args_parser.add_positional_argument(command_input, "Command", "command_input", Core::ArgsParser::Required::Yes);
+    args_parser.add_positional_argument(filepaths, "File", "file", Core::ArgsParser::Required::No);
+
+    args_parser.parse(args);
+
+    auto command = TRY(parse_command(command_input));
+
+    if (filepaths.is_empty())
+        filepaths = { "-"sv };
+
+    Array<u8, PAGE_SIZE> buffer {};
+    for (auto const& filepath : filepaths) {
+        auto file_unbuffered = TRY(Core::Stream::File::open_file_or_standard_stream(filepath, Core::Stream::OpenMode::Read));
+        auto file = TRY(Core::Stream::BufferedFile::create(move(file_unbuffered)));
+
+        while (!file->is_eof()) {
+            auto line = TRY(file->read_line(buffer));
+
+            // Substitutions can apply to blank lines in the middle of a file,
+            // but not to the trailing newline that marks the end of a file.
+            if (line.is_empty() && file->is_eof())
+                break;
+
+            auto result = command.regex.replace(line, command.replacement, command.options);
+            outln(result);
+        }
+    }
+
+    return 0;
+}