docs: move extensions and incompatibilities to docs/src/extensions.md

Start an mdBook under docs/, laid out as in coreutils, and move the list of
extensions and incompatibilities out of the README into it. The README keeps
a pointer.

A Documentation workflow builds the book with mdbook 0.5.0, the version the
uutils website uses, whenever docs/ changes, and uploads it as an artifact.
mdbook 0.5 rejects the `multilingual` field coreutils still carries (the
website strips it before building), so the book leaves it out.

.github/workflows/GnuTests.yml

@@ -49,6 +49,19 @@ jobs:
 
     # Omit installing part of https://github.com/actions/runner-images/tree/main/images/ubuntu
 
+    ### Locales
+    # Several testsuite scripts guard themselves with require_*_locale_ and
+    # silently skip when the locale is missing, which hides both regressions
+    # and improvements in the multibyte code paths.
+    - name: Generate the locales required by the testsuite
+      shell: bash
+      run: |
+        ## Generate the locales required by the testsuite
+        sudo localedef -i en_US -f UTF-8 en_US.UTF-8
+        sudo localedef -i ru_RU -f UTF-8 ru_RU.UTF-8
+        sudo localedef -i el_GR -f ISO-8859-7 el_GR.iso88597
+        locale -a
+
     ### Build
     - name: Build Rust sed binary
       shell: bash
@@ -134,7 +147,7 @@ jobs:
         persist-credentials: false
 
     - name: Retrieve reference artifacts
-      uses: dawidd6/action-download-artifact@v21
+      uses: dawidd6/action-download-artifact@v25
       continue-on-error: true
       with:
         workflow: GnuTests.yml

.github/workflows/documentation.yml

@@ -0,0 +1,41 @@
+name: Documentation
+
+on:
+  pull_request:
+    paths:
+      - 'docs/**'
+      - '.github/workflows/documentation.yml'
+  push:
+    branches:
+      - main
+    paths:
+      - 'docs/**'
+      - '.github/workflows/documentation.yml'
+
+permissions:
+  contents: read
+
+jobs:
+  build-doc:
+    name: Build the mdBook documentation
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+
+      - name: Install mdbook
+        uses: taiki-e/install-action@v2
+        with:
+          tool: mdbook@0.5.0
+
+      - name: Build documentation
+        run: mdbook build docs
+
+      - name: Upload documentation
+        uses: actions/upload-artifact@v7
+        with:
+          name: documentation
+          path: docs/book

.github/workflows/release.yml

@@ -64,7 +64,7 @@ jobs:
         # we specify bash to get pipefail; it guards against the `curl` command
         # failing. otherwise `sh` won't catch that `curl` returned non-0
         shell: bash
-        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.30.3/cargo-dist-installer.sh | sh"
+        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.33.0/cargo-dist-installer.sh | sh"
       - name: Cache dist
         uses: actions/upload-artifact@v7
         with:

Cargo.toml

@@ -20,6 +20,19 @@ rust-version = "1.88"
 
 build = "build.rs"
 
+# cargo-binstall: fetch the archives published by `dist` in the GitHub releases
+# instead of building from source. The layout below has to stay in sync with
+# `dist-workspace.toml` (targets) and the archives it produces:
+#   sed-<target>.tar.xz (zip on Windows), containing a sed-<target>/ directory.
+# Note that the release tags carry no `v` prefix, hence `{ version }`.
+[package.metadata.binstall]
+pkg-url = "{ repo }/releases/download/{ version }/{ name }-{ target }.{ archive-suffix }"
+bin-dir = "{ name }-{ target }/{ bin }{ binary-ext }"
+pkg-fmt = "txz"
+
+[package.metadata.binstall.overrides.x86_64-pc-windows-msvc]
+pkg-fmt = "zip"
+
 [features]
 default = ["feat_common_core"]
 
@@ -45,11 +58,11 @@ phf_codegen = "0.14.0"
 predicates = "3.1.3"
 rand = { version = "0.10.0" }
 regex = "1.10.4"
-sha2 = "0.11"
+sha2 = { version = "0.11.0", default-features = false, features = ["alloc"] }
 tempfile = "3.10.1"
 terminal_size = "0.4.2"
 textwrap = { version = "0.16.1", features = ["terminal_size"] }
-uucore = { version = "0.10.0", features = ["libc"] }
+uucore = { version = "0.12.0", features = ["libc"] }
 rustix = "1.1.4"
 xattr = "1.3.1"
 
@@ -83,7 +96,7 @@ regex = { workspace = true }
 sha2 = { workspace = true }
 tempfile = { workspace = true }
 uucore = { workspace = true, features = ["entries", "process", "signals", "benchmark"] }
-uutests = "0.10.0"
+uutests = "0.12.0"
 
 [target.'cfg(unix)'.dev-dependencies]
 xattr = { workspace = true }
@@ -117,6 +130,10 @@ inherits = "release"
 opt-level = "z"
 strip = true
 
+# The profile that 'dist' will build with
+[profile.dist]
+inherits = "release"
+
 [lints.clippy]
 all = { level = "warn", priority = -1 }
 

README.md

@@ -15,22 +15,30 @@ and other extensions.
 ## Status
 
 At this state _sed_ implements all [POSIX features](https://pubs.opengroup.org/onlinepubs/9799919799/)
-and can run correctly the two complex scripts of its integration tests:
-[hanoi.sed](https://github.com/uutils/sed/blob/main/tests/fixtures/sed/script/hanoi.sed) (solves the Towers of Hanoi puzzle) and
+and can run correctly the three complex scripts of its integration tests:
+[hanoi.sed](https://github.com/uutils/sed/blob/main/tests/fixtures/sed/script/hanoi.sed) (solves the Towers of Hanoi puzzle),
+[mandelbrot.sed](https://github.com/uutils/sed/blob/main/tests/fixtures/sed/script/mandelbrot.sed), (draws the Mandelbrot set) and
 [math.sed](https://github.com/uutils/sed/blob/main/tests/fixtures/sed/script/math.sed)  (implements an arbitrary precision integer math calculator).
 
 The performance of this Rust implementation is now better than the GNU and FreeBSD implementations for most benchmarked cases.
 
 Further work aims to:
-* Adjust buffering on terminal output to match current implementations,
-* Implement more GNU extensions,
-* Improve performance where possible.
+* improve GNU _sed_ compatibility, especially on the regular expression front,
+* implement more GNU extensions, and
+* improve performance where possible.
 
 ## Installation and Use
 
 We provide a Linux x86_64 binary archive from the main branch at
 https://github.com/uutils/sed/releases/tag/latest-commit .
 
+If you have [cargo-binstall](https://github.com/cargo-bins/cargo-binstall),
+the released binaries can be installed directly with:
+
+```bash
+cargo binstall sed
+```
+
 For other platforms, ensure you have Rust installed on your system. You can install Rust through [rustup](https://rustup.rs/).
 
 Clone the repository and build the project using Cargo:
@@ -80,65 +88,8 @@ cargo test
 ```
 
 ## Extensions and incompatibilities
-### Supported GNU extensions
-* Command-line arguments can be specified in long (`--`) form.
-* Spaces can precede a regular expression modifier.
-* `I` can be used in as a synonym for the `i` (case insensitive) substitution
-  flag.
-* `M` and `m` substitution flags allow multi-line matching.
-* In addition to `\n`, other escape sequences (octal, hex, C) are supported
-  in the strings of the `y` command.
-  Under POSIX these yield undefined behavior.
-* The `a`, `c`, and `i` commands do not require an initial backslash,
-  allow text to appear on the same line, and support escape sequences
-  in the specified text.
-* The `a`, `i`, `=`, `l`, `q` and `r` commands support address range as an extension to POSIX.
-* The substitution command replacement group `\0` is a synonym for &.
-* A `Q` command (optionally followed by an exit code) quits immediately.
-* The `q` command can be optionally followed by an exit code.
-* The `l` command can be optionally followed by the output width.
-* The `--follow-symlinks` option for in-place editing.
-* The `--sandbox` option that limits potentially destructive commands.
-* Address 0 can be used to specify an address range that is already
-  active on line 1 and can finish with the specified regular expression.
-* Address steps can be specified in the form of start~step and start,~step
-  ranges.
-* Address 0 can be used in the `r` command to prepend a file.
-
-### Supported BSD and GNU extensions
-* The second address in a range can be specified as a relative address with +N.
-* In-place editing of file with the `-i` flag.
-
-### New extensions
-* Unicode characters can be specified in regular expression pattern, replacement
-  and transliteration sequences using `\uXXXX` or `\UXXXXXXXX` sequences.
-* The `l` command lists Unicode characters using the `\uXXXX` and `\UXXXXXXXX`
-  sequences.
-
-### Incompatibilities
-* Similarly to GNU _sed_, input is processed as raw bytes or as valid UTF-8
-  (this includes 7-bit ASCII) based on the locale as specified by the
-  `LC_ALL`, `LC_CTYPE`, and `LANG` environment variables,
-  with the default being byte processing.
-  However, in contrast with GNU _sed_, other locales (e.g. ISO-8859-1)
-  are not supported. If the input is in another code page or encoding
-  and requires locale-specific processing (e.g. ignore/map case,
-  character classes), consider converting it through UTF-8 to ensure
-  the correct handling of locale-specific regular expressions.
-  This _sed_ program can also handle arbitrary byte sequences
-  if no part of the input requires treating it as a Rust String.
-* Back-references aren't supported when input is processed as bytes
-  (`LC_ALL=C`).
-* The command will report an error and fail if duplicate labels are found
-  in the script.
-  This matches the BSD behavior. The GNU version accepts duplicate labels.
-* The last line (`$`) address is interpreted as the last non-empty line of
-  the last file.  If files specified in subsequent arguments until the last
-  one are empty, then the last line condition will never be triggered.
-  This behavior is consistent with the
-  [original implementation](https://github.com/dspinellis/unix-history-repo/blob/Research-V7/usr/src/cmd/sed/sed1.c#L665).
-* Labels are parsed for alphanumeric characters. The BSD version parses them
-  until the end of the line, preventing ; to be used as a separator.
+The GNU, BSD and new extensions _sed_ supports, and where it differs from GNU
+_sed_, are listed in [docs/src/extensions.md](docs/src/extensions.md).
 
 ## GNU test suite compatibility
 

dist-workspace.toml

@@ -4,7 +4,7 @@ members = ["cargo:."]
 # Config for 'dist'
 [dist]
 # The preferred dist version to use in CI (Cargo.toml SemVer syntax)
-cargo-dist-version = "0.30.3"
+cargo-dist-version = "0.33.0"
 # CI backends to support
 ci = "github"
 # The installers to generate for each app
@@ -13,5 +13,5 @@ installers = []
 targets = ["aarch64-apple-darwin", "aarch64-unknown-linux-gnu", "x86_64-apple-darwin", "x86_64-unknown-linux-gnu", "x86_64-unknown-linux-musl", "x86_64-pc-windows-msvc"]
 # Which actions to run on pull requests
 pr-run-mode = "plan"
-# Allow dirty workflows to ignore out-of-date contents
+# Skip checking whether the specified configuration files are up to date
 allow-dirty = ["ci"]

docs/.gitignore

@@ -0,0 +1 @@
+book

docs/book.toml

@@ -0,0 +1,7 @@
+[book]
+language = "en"
+src = "src"
+title = "uutils sed Documentation"
+
+[output.html]
+git-repository-url = "https://github.com/uutils/sed/tree/main/docs/src"

docs/src/SUMMARY.md

@@ -0,0 +1,5 @@
+# Summary
+
+[Introduction](index.md)
+
+* [Extensions and incompatibilities](extensions.md)

docs/src/extensions.md

@@ -0,0 +1,73 @@
+# Extensions and incompatibilities
+
+The main goal of the project is compatibility with GNU _sed_, but _sed_ also
+supports features that GNU _sed_ does not, and differs from it in a few places.
+Below is a list of these extensions and incompatibilities.
+
+## Supported GNU extensions
+* Command-line arguments can be specified in long (`--`) form.
+* Spaces can precede a regular expression modifier.
+* `I` can be used in as a synonym for the `i` (case insensitive) substitution
+  flag.
+* `M` and `m` substitution flags allow multi-line matching.
+* In addition to `\n`, other escape sequences (octal, hex, C) are supported
+  in the strings of the `y` command.
+  Under POSIX these yield undefined behavior.
+* The `a`, `c`, and `i` commands do not require an initial backslash,
+  allow text to appear on the same line, and support escape sequences
+  in the specified text.
+* The `a`, `i`, `=`, `l`, `q` and `r` commands support address range as an extension to POSIX.
+* The substitution command replacement group `\0` is a synonym for &.
+* An `F` command outputs the name of the file currently being processed.
+* A `Q` command (optionally followed by an exit code) quits immediately.
+* The `q` command can be optionally followed by an exit code.
+* A `W` command writes to a file the pattern's first line.
+* An `R` command reads one line at a time from a file.
+* The `l` command can be optionally followed by the output width.
+* The `--follow-symlinks` option for in-place editing.
+* The `--sandbox` option that limits potentially destructive commands.
+* Address 0 can be used to specify an address range that is already
+  active on line 1 and can finish with the specified regular expression.
+* Address steps can be specified in the form of start~step and start,~step
+  ranges.
+* Address 0 can be used in the `r` command to prepend a file.
+
+## Supported BSD and GNU extensions
+* The second address in a range can be specified as a relative address with +N.
+* In-place editing of file with the `-i` flag.
+
+## New extensions
+* Unicode characters can be specified in regular expression pattern, replacement
+  and transliteration sequences using `\uXXXX` or `\UXXXXXXXX` sequences.
+
+## Incompatible extensions
+The `-U` or `--uutil-extensions` option enables useful extensions or bug fixes
+that aren't compatible with GNU sed or POSIX.
+
+* The `l` command lists Unicode characters using the `\uXXXX` and `\UXXXXXXXX`
+  escapes rather than as octal UTF-8 byte sequences.
+
+## Incompatibilities
+* Similarly to GNU _sed_, input is processed as raw bytes or as valid UTF-8
+  (this includes 7-bit ASCII) based on the locale as specified by the
+  `LC_ALL`, `LC_CTYPE`, and `LANG` environment variables,
+  with the default being byte processing.
+  However, in contrast with GNU _sed_, other locales (e.g. ISO-8859-1)
+  are not supported. If the input is in another code page or encoding
+  and requires locale-specific processing (e.g. ignore/map case,
+  character classes), consider converting it through UTF-8 to ensure
+  the correct handling of locale-specific regular expressions.
+  This _sed_ program can also handle arbitrary byte sequences
+  if no part of the input requires treating it as a Rust String.
+* Back-references aren't supported when input is processed as bytes
+  (`LC_ALL=C`).
+* The command will report an error and fail if duplicate labels are found
+  in the script.
+  This matches the BSD behavior. The GNU version accepts duplicate labels.
+* The last line (`$`) address is interpreted as the last non-empty line of
+  the last file.  If files specified in subsequent arguments until the last
+  one are empty, then the last line condition will never be triggered.
+  This behavior is consistent with the
+  [original implementation](https://github.com/dspinellis/unix-history-repo/blob/Research-V7/usr/src/cmd/sed/sed1.c#L665).
+* Labels are parsed for alphanumeric characters. The BSD version parses them
+  until the end of the line, preventing ; to be used as a separator.

docs/src/index.md

@@ -0,0 +1,10 @@
+# uutils sed
+
+_sed_ is a Rust reimplementation of the
+[sed utility](https://pubs.opengroup.org/onlinepubs/9799919799/utilities/sed.html)
+with some [GNU sed](https://www.gnu.org/software/sed/manual/sed.html),
+[FreeBSD sed](https://man.freebsd.org/cgi/man.cgi?sed(1)),
+and other extensions.
+
+It is part of the [uutils](https://uutils.github.io/) project. The source code
+is on [GitHub](https://github.com/uutils/sed).

fuzz/Cargo.lock

@@ -245,9 +245,9 @@ checksum = "1d07550c9036bf2ae0c684c4297d503f838287c83c53686d05370d0e139ae570"
 
 [[package]]
 name = "console"
-version = "0.16.4"
+version = "0.16.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4fe5f465a4f6fee88fad41b85d990f84c835335e85b5d9e6e63e0d06d28cba7c"
+checksum = "e96a4956774c13c126a8b5af4daa79384f4d826534c95a02d76afb39e2ab64e3"
 dependencies = [
  "encode_unicode",
  "libc",
@@ -820,9 +820,9 @@ checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
 
 [[package]]
 name = "rand"
-version = "0.10.2"
+version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c7f5fa3a058cd35567ef9bfa5e75732bee0f9e4c55fa90477bef2dfcdbc4be80"
+checksum = "65c9fb96cbc91e3478eaae79a69fcd3f1ae4ad052e471fe6732fff548984b4af"
 dependencies = [
  "chacha20",
  "getrandom 0.4.2",
@@ -897,7 +897,7 @@ checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
 [[package]]
 name = "sed"
-version = "0.1.1"
+version = "0.2.0"
 dependencies = [
  "clap",
  "clap_complete",
@@ -985,9 +985,9 @@ checksum = "703d5c7ef118737c72f1af64ad2f6f8c5e1921f818cdcb97b8fe6fc69bf66214"
 
 [[package]]
 name = "similar"
-version = "3.1.2"
+version = "3.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "85ee016af5d736b69fc89e19254540fa4b5f5492853fb5503920f084011c78b6"
+checksum = "4f66ca1f7aca2474dc10c942eb22feffc897735f54cd1db90138c2fddb490987"
 dependencies = [
  "bstr",
 ]
@@ -1034,7 +1034,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
 dependencies = [
  "fastrand",
- "getrandom 0.4.2",
+ "getrandom 0.3.4",
  "once_cell",
  "rustix",
  "windows-sys",
@@ -1152,9 +1152,9 @@ checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
 
 [[package]]
 name = "uucore"
-version = "0.10.0"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e97dd0fd8bb2ed12affba9f956c3b94b8ad3f9432746717475420e916ae0b8d4"
+checksum = "f24a5910ebbf2c0baf486a9125705f8e026a8f7741a3ea8cf5eca3c9257c9bdf"
 dependencies = [
  "bigdecimal",
  "clap",
@@ -1167,7 +1167,6 @@ dependencies = [
  "os_display",
  "procfs",
  "rustc-hash",
- "rustix",
  "thiserror",
  "unic-langid",
  "unicode-width",
@@ -1192,9 +1191,9 @@ dependencies = [
 
 [[package]]
 name = "uucore_procs"
-version = "0.10.0"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "907f1b828046ea42cdb4bd898f05b48ab873a41937bf75ebe12f09a5bf411f58"
+checksum = "50aa1f3bba55168888ae6f1f2714ce58897d8020d742d21f474f01e86468fedd"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1202,9 +1201,9 @@ dependencies = [
 
 [[package]]
 name = "uufuzz"
-version = "0.10.0"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72d4c5bac0f8ccabaa8e8ccbf2724446f8b007c06ad343fabfe1a1525a4ff4f2"
+checksum = "7147da7bd2de08e6647116e005b0992cc602e34c34972793844a45c4e8648dd9"
 dependencies = [
  "console",
  "rand",

fuzz/Cargo.toml

@@ -14,8 +14,8 @@ libc = "0.2.153"
 tempfile = "3.15.0"
 rand = { version = "0.10.0" }
 similar = "3.0.0"
-uucore = { version = "0.10.0", features = ["libc"] }
-uufuzz = "0.10.0"
+uucore = { version = "0.12.0", features = ["libc"] }
+uufuzz = "0.12.0"
 
 sed = { path = ".." }
 

src/sed/command.rs

@@ -10,6 +10,7 @@
 
 use crate::sed::error_handling::{ScriptLocation, runtime_error};
 use crate::sed::fast_regex::{Captures, Match, Regex};
+use crate::sed::named_reader::NamedReader;
 use crate::sed::named_writer::NamedWriter;
 use crate::sed::script_char_provider::ScriptCharProvider;
 use crate::sed::script_line_provider::ScriptLineProvider;
@@ -38,10 +39,11 @@ pub struct ProcessingContext {
     pub sandbox: bool,
     pub unbuffered: bool,
     pub null_data: bool,
+    pub uutil_extensions: bool,
 
     // Other context
-    /// Currently processed input file name (not script) in quoted form
-    pub input_name: String,
+    /// Currently processed input file name (not script)
+    pub input_name: PathBuf,
     /// Current input line number
     pub line_number: usize,
     /// True if this is the last address of a range
@@ -66,6 +68,9 @@ pub struct ProcessingContext {
     pub parsed_block_nesting: usize,
     /// Command associated with each label
     pub label_to_command_map: HashMap<String, Rc<RefCell<Command>>>,
+    /// Shared `R` readers keyed by file path, so that all `R` commands naming
+    /// the same file advance a single cursor, matching GNU sed.
+    pub named_readers: HashMap<PathBuf, Rc<RefCell<NamedReader>>>,
     /// Commands with a (latchable and resetable) address range
     pub range_commands: Vec<Rc<RefCell<Command>>>,
     /// True if a substitution was made as specified in the t command
@@ -367,6 +372,7 @@ pub enum CommandData {
     BranchTarget(Option<Rc<RefCell<Command>>>), // Commands for 'b', 't', 'T', '{'
     Label(Option<String>),                      // Label name for 'b', 't', 'T', ':'
     Path(PathBuf),                              // File path for 'r'
+    NamedReader(Rc<RefCell<NamedReader>>),      // Successive file lines for 'R'
     NamedWriter(Rc<RefCell<NamedWriter>>),      // File output for 'w'
     Number(usize),                              // Number for 'l', 'q', 'Q' (GNU)
     Substitution(Box<Substitution>),            // Substitute command 's'

src/sed/compiler.rs

@@ -18,6 +18,7 @@ use crate::sed::delimited_parser::{
 };
 use crate::sed::error_handling::{ScriptLocation, compilation_error, semantic_error};
 use crate::sed::fast_regex::Regex;
+use crate::sed::named_reader::NamedReader;
 use crate::sed::named_writer::NamedWriter;
 use crate::sed::script_char_provider::ScriptCharProvider;
 use crate::sed::script_line_provider::{ScriptLineProvider, ScriptValue};
@@ -1122,6 +1123,28 @@ fn compile_read_file_command(
     Ok(CommandHandling::Continue)
 }
 
+// Handles R
+fn compile_read_line_command(
+    lines: &mut ScriptLineProvider,
+    line: &mut ScriptCharProvider,
+    cmd: &mut Command,
+    context: &mut ProcessingContext,
+) -> UResult<CommandHandling> {
+    if context.sandbox {
+        return compilation_error(lines, line, ERR_SANDBOX);
+    }
+    let path = read_file_path(lines, line)?;
+    // Reuse a reader keyed by path so all `R` commands on the same file share
+    // one cursor (see `ProcessingContext::named_readers`).
+    let reader = context
+        .named_readers
+        .entry(path.clone())
+        .or_insert_with(|| NamedReader::new(path))
+        .clone();
+    cmd.data = CommandData::NamedReader(reader);
+    Ok(CommandHandling::Continue)
+}
+
 // Handles w
 fn compile_write_file_command(
     lines: &mut ScriptLineProvider,
@@ -1632,6 +1655,14 @@ fn get_cmd_spec(
             n_addr: 2,
             handler: compile_execute_command,
         }),
+        'F' if !posix => Ok(CommandSpec {
+            n_addr: 2,
+            handler: compile_empty_command,
+        }),
+        'R' if !posix => Ok(CommandSpec {
+            n_addr: 2,
+            handler: compile_read_line_command,
+        }),
         'r' => Ok(CommandSpec {
             n_addr: if posix { 1 } else { 2 },
             handler: compile_read_file_command,
@@ -1644,6 +1675,10 @@ fn get_cmd_spec(
             n_addr: 2,
             handler: compile_label_command,
         }),
+        'W' if !posix => Ok(CommandSpec {
+            n_addr: 2,
+            handler: compile_write_file_command,
+        }),
         'w' => Ok(CommandSpec {
             n_addr: 2,
             handler: compile_write_file_command,
@@ -3013,6 +3048,31 @@ mod tests {
         assert!(err.to_string().contains(ERR_SANDBOX));
     }
 
+    // compile_read_line_command (R)
+    #[test]
+    fn test_compile_read_line_command_rejected_under_sandbox() {
+        let (mut lines, mut chars) = make_providers("R input.txt");
+        let mut cmd = Command::default();
+        let mut context = ctx();
+        context.sandbox = true;
+
+        let err =
+            compile_read_line_command(&mut lines, &mut chars, &mut cmd, &mut context).unwrap_err();
+        assert!(err.to_string().contains(ERR_SANDBOX));
+    }
+
+    #[test]
+    fn test_compile_read_line_command_sets_named_reader() {
+        let (mut lines, mut chars) = make_providers("R input.txt");
+        let mut cmd = Command::default();
+        let mut context = ctx();
+
+        let handling =
+            compile_read_line_command(&mut lines, &mut chars, &mut cmd, &mut context).unwrap();
+        assert!(matches!(handling, CommandHandling::Continue));
+        assert!(matches!(cmd.data, CommandData::NamedReader(_)));
+    }
+
     // compile_write_file_command
     #[test]
     fn test_compile_write_file_command_rejected_under_sandbox() {

src/sed/error_handling.rs

@@ -14,6 +14,7 @@ use crate::sed::script_line_provider::ScriptLineProvider;
 
 use std::rc::Rc;
 
+use uucore::display::Quotable;
 use uucore::error::{UResult, USimpleError};
 
 #[derive(Clone, Debug)]
@@ -108,7 +109,7 @@ pub fn input_runtime_error<T>(
             location.input_name,
             location.line_number,
             location.column_number,
-            context.input_name,
+            context.input_name.quote(),
             context.line_number,
             msg.to_string()
         ),

src/sed/mod.rs

@@ -15,6 +15,7 @@ pub mod error_handling;
 pub mod fast_io;
 pub mod fast_regex;
 pub mod in_place;
+pub mod named_reader;
 pub mod named_writer;
 pub mod processor;
 pub mod script_char_provider;
@@ -114,6 +115,11 @@ pub fn uu_app() -> Command {
             arg!(-s --separate "Consider files as separate rather than as a long stream."),
             arg!(--sandbox "Operate in a sandbox by disabling e/r/w commands."),
             arg!(-u --unbuffered "Load minimal input data and flush output buffers regularly."),
+            Arg::new("uutil-extensions")
+                .short('U')
+                .long("uutil-extensions")
+                .help("Enable incompatible extensions.")
+                .action(clap::ArgAction::SetTrue),
             Arg::new("null-data")
                 .short('z')
                 .long("null-data")
@@ -239,16 +245,17 @@ fn build_context(matches: &ArgMatches) -> UResult<ProcessingContext> {
         length: matches.get_one::<u32>("length").map_or(70, |v| *v as usize),
         quiet: matches.get_flag("quiet"),
         posix: matches.get_flag("posix"),
-        separate: matches.get_flag("separate"),
+        separate: matches.get_flag("separate") || matches.contains_id("in-place"),
         sandbox: matches.get_flag("sandbox"),
         unbuffered: matches.get_flag("unbuffered"),
         null_data: matches.get_flag("null-data"),
+        uutil_extensions: matches.get_flag("uutil-extensions"),
 
         // Environment
         character_mode: character_mode_for_locale(&locale)?,
 
         // Other context
-        input_name: "<stdin>".to_string(),
+        input_name: PathBuf::from("-"),
         line_number: 0,
         last_address: false,
         last_line: false,
@@ -262,6 +269,7 @@ fn build_context(matches: &ArgMatches) -> UResult<ProcessingContext> {
         },
         parsed_block_nesting: 0,
         label_to_command_map: HashMap::new(),
+        named_readers: HashMap::new(),
         range_commands: Vec::new(),
         substitution_made: false,
         append_elements: Vec::new(),
@@ -389,6 +397,7 @@ mod tests {
         assert!(!ctx.sandbox);
         assert!(!ctx.unbuffered);
         assert!(!ctx.null_data);
+        assert!(!ctx.uutil_extensions);
     }
 
     #[test]
@@ -406,6 +415,7 @@ mod tests {
             "-s",
             "--sandbox",
             "-u",
+            "-U",
             "-z",
         ]);
 
@@ -424,6 +434,7 @@ mod tests {
         assert!(ctx.sandbox);
         assert!(ctx.unbuffered);
         assert!(ctx.null_data);
+        assert!(ctx.uutil_extensions);
     }
 
     #[test]

src/sed/named_reader.rs

@@ -0,0 +1,101 @@
+// An abstraction for input files read one line at a time by the `R` command
+//
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2025 Diomidis Spinellis
+//
+// This file is part of the uutils sed package.
+// It is licensed under the MIT License.
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
+use std::cell::RefCell;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::path::PathBuf;
+use std::rc::Rc;
+
+#[derive(Debug)]
+/// State of the file backing an `R` command, opened lazily on first use.
+enum State {
+    Unopened,
+    Open(BufReader<File>),
+    Exhausted,
+}
+
+#[derive(Debug)]
+/// Reader that yields successive lines of a file for the GNU `R` command.
+/// The file is opened on first use; a file that cannot be opened or read is
+/// treated as having no more lines, matching GNU sed (no error is raised).
+pub struct NamedReader {
+    path: PathBuf,
+    state: State,
+}
+
+impl NamedReader {
+    /// Create a reader for `path` without opening it yet.
+    pub fn new(path: PathBuf) -> Rc<RefCell<Self>> {
+        Rc::new(RefCell::new(NamedReader {
+            path,
+            state: State::Unopened,
+        }))
+    }
+
+    /// Return the next line of the file, including its trailing newline if
+    /// present, or `None` once the file is exhausted or could not be read.
+    pub fn next_line(&mut self) -> Option<Vec<u8>> {
+        if matches!(self.state, State::Unopened) {
+            self.state = match File::open(&self.path) {
+                Ok(file) => State::Open(BufReader::new(file)),
+                Err(_) => State::Exhausted,
+            };
+        }
+
+        let State::Open(reader) = &mut self.state else {
+            return None;
+        };
+
+        let mut line = Vec::new();
+        match reader.read_until(b'\n', &mut line) {
+            Ok(0) | Err(_) => {
+                self.state = State::Exhausted;
+                None
+            }
+            Ok(_) => Some(line),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+    use tempfile::NamedTempFile;
+
+    #[test]
+    fn yields_successive_lines_then_none() {
+        let mut file = NamedTempFile::new().unwrap();
+        file.write_all(b"one\ntwo\n").unwrap();
+        let reader = NamedReader::new(file.path().to_path_buf());
+
+        assert_eq!(reader.borrow_mut().next_line(), Some(b"one\n".to_vec()));
+        assert_eq!(reader.borrow_mut().next_line(), Some(b"two\n".to_vec()));
+        assert_eq!(reader.borrow_mut().next_line(), None);
+        assert_eq!(reader.borrow_mut().next_line(), None);
+    }
+
+    #[test]
+    fn last_line_without_newline_is_preserved() {
+        let mut file = NamedTempFile::new().unwrap();
+        file.write_all(b"abc").unwrap();
+        let reader = NamedReader::new(file.path().to_path_buf());
+
+        assert_eq!(reader.borrow_mut().next_line(), Some(b"abc".to_vec()));
+        assert_eq!(reader.borrow_mut().next_line(), None);
+    }
+
+    #[test]
+    fn missing_file_yields_no_lines() {
+        let reader = NamedReader::new(PathBuf::from("/nonexistent/xyzzy-42-does-not-exist"));
+        assert_eq!(reader.borrow_mut().next_line(), None);
+    }
+}

src/sed/named_writer.rs

@@ -55,16 +55,22 @@ impl NamedWriter {
         Ok(writer)
     }
 
-    /// Write a line to the file with a newline, returning descriptive errors.
-    pub fn write_line(&mut self, line: &str) -> UResult<()> {
-        self.write_line_bytes(line.as_bytes())
+    /// Write String to the file, possibly with a newline, returning errors.
+    pub fn write_line(&mut self, line: &str, newline: bool) -> UResult<()> {
+        self.write_line_bytes(line.as_bytes(), newline)
     }
 
-    /// Write bytes to the file with a newline, returning descriptive errors.
-    pub fn write_line_bytes(&mut self, line: &[u8]) -> UResult<()> {
+    /// Write bytes to the file, possibly with a newline, returning errors.
+    pub fn write_line_bytes(&mut self, line: &[u8], newline: bool) -> UResult<()> {
         self.writer
             .write_all(line)
-            .and_then(|()| self.writer.write_all(b"\n"))
+            .and_then(|()| {
+                if newline {
+                    self.writer.write_all(b"\n")
+                } else {
+                    Ok(())
+                }
+            })
             .map_err(|e| {
                 runtime_error::<()>(
                     &self.location,
@@ -109,9 +115,27 @@ mod tests {
         let path = file.path().to_path_buf();
         let writer = NamedWriter::new(path.clone(), ScriptLocation::default()).unwrap();
 
-        writer.borrow_mut().write_line_bytes(b"a\xE9").unwrap();
+        writer
+            .borrow_mut()
+            .write_line_bytes(b"a\xE9", true)
+            .unwrap();
         writer.borrow_mut().flush().unwrap();
 
         assert_eq!(fs::read(path).unwrap(), b"a\xE9\n");
     }
+
+    #[test]
+    fn test_write_line_bytes_appends_no_newline() {
+        let file = NamedTempFile::new().unwrap();
+        let path = file.path().to_path_buf();
+        let writer = NamedWriter::new(path.clone(), ScriptLocation::default()).unwrap();
+
+        writer
+            .borrow_mut()
+            .write_line_bytes(b"a\xE9", false)
+            .unwrap();
+        writer.borrow_mut().flush().unwrap();
+
+        assert_eq!(fs::read(path).unwrap(), b"a\xE9");
+    }
 }