fix(builtins): xargs and empty pipes give stdin at EOF; printf %q keeps UTF-8 text

crates/bashkit/src/builtins/generated/format_support.rs

@@ -104,14 +104,17 @@ fn shell_quote(s: &str) -> String {
         return "''".to_string();
     }
 
-    let needs_quoting = s
-        .chars()
-        .any(|c| !c.is_ascii_alphanumeric() && !"_/.:-=+@,%^".contains(c));
+    // Under UTF-8, bash leaves printable non-ASCII characters as they are
+    // (`printf %q 'com espaço'` is `com\ espaço`).
+    let safe = |c: char| {
+        c.is_ascii_alphanumeric() || "_/.:-=+@,%^".contains(c) || (!c.is_ascii() && !c.is_control())
+    };
+    let needs_quoting = s.chars().any(|c| !safe(c));
     if !needs_quoting {
         return s.to_string();
     }
 
-    let has_control = s.chars().any(|c| (c as u32) < 32 || c as u32 == 127);
+    let has_control = s.chars().any(char::is_control);
     if has_control {
         let mut out = String::from("$'");
         for ch in s.chars() {
@@ -124,6 +127,12 @@ fn shell_quote(s: &str) -> String {
                 c if (c as u32) < 32 || c as u32 == 127 => {
                     out.push_str(&format!("\\x{:02x}", c as u32));
                 }
+                c if c.is_control() => {
+                    let mut buf = [0u8; 4];
+                    for b in c.encode_utf8(&mut buf).bytes() {
+                        out.push_str(&format!("\\{b:03o}"));
+                    }
+                }
                 c => out.push(c),
             }
         }
@@ -133,7 +142,7 @@ fn shell_quote(s: &str) -> String {
 
     let mut out = String::new();
     for ch in s.chars() {
-        if ch.is_ascii_alphanumeric() || "_/.:-=+@,%^".contains(ch) {
+        if safe(ch) {
             out.push(ch);
         } else {
             out.push('\\');

crates/bashkit/src/builtins/pipeline.rs

@@ -536,7 +536,10 @@ impl XargsOptions {
                 SubCommand {
                     name,
                     args: cmd,
-                    stdin: None,
+                    // GNU xargs gives each command /dev/null as stdin: the
+                    // items are already consumed (`printf '' | xargs wc -l`
+                    // prints 0).
+                    stdin: Some(crate::StreamData::new()),
                     assignments: match self.process_slot_var {
                         Some(ref var) => vec![(var.clone(), (idx % slot_count).to_string())],
                         None => Vec::new(),

crates/bashkit/src/interpreter/mod.rs

@@ -7227,7 +7227,9 @@ impl Interpreter {
             let stdin = if stdin.is_some() {
                 stdin
             } else if let Some(ref ps) = self.pipeline_stdin {
-                if !ps.is_empty() {
+                // An empty pipe is still stdin at EOF: `printf '' | { wc -l; }`
+                // prints 0, not nothing.
+                {
                     if name == "read" {
                         // Consume one record (line, `-d` delimiter, `-n` count,
                         // `\<newline>` continuation) from pipeline stdin.
@@ -7239,8 +7241,6 @@ impl Interpreter {
                     } else {
                         Some(ps.clone())
                     }
-                } else {
-                    None
                 }
             } else {
                 None

crates/bashkit/tests/spec_cases/bash/bash-stdin-pipe.test.sh

@@ -20,3 +20,11 @@ echo "test input" | bash /tmp/read_test.sh
 ### expect
 line: test input
 ### end
+
+### empty_pipe_is_stdin_at_eof_for_compound_commands
+printf '' | { wc -l; }
+f() { wc -l; }; printf '' | f
+### expect
+0
+0
+### end

crates/bashkit/tests/spec_cases/bash/printf.test.sh

@@ -282,3 +282,10 @@ printf '\xff\xfe' | od -An -tx1
 ### expect
  ff fe
 ### end
+
+### printf_q_keeps_printable_non_ascii
+printf '%q\n' 'com espaço' 'a€b'
+### expect
+com\ espaço
+a€b
+### end

crates/bashkit/tests/spec_cases/bash/xargs.test.sh

@@ -95,3 +95,13 @@ printf "x\n" | xargs -r echo got
 ### expect
 got x
 ### end
+
+### xargs_empty_input_runs_command_once_with_empty_stdin
+# GNU xargs without -r runs the command once; its stdin is at EOF
+printf '' | xargs wc -l
+printf '' | xargs -r wc -l
+echo done
+### expect
+0
+done
+### end

knowledge/log.md

@@ -91,6 +91,7 @@
 * **Fix**: Declaration builtins and local scope match bash. `declare`/`typeset`/`local`/`export`/`readonly` share one engine with bash's option sets, errors and `declare -p` format (quoting, assoc hash order); locals use shallow binding saved in the call frame, so nested functions, `unset` of a caller's local, `declare -g` past a local, and `local -n` behave as in bash. Compound operands stay one `CompoundAssignment` word part (keyed `[k]="v w"` and `` [k]=`cmd` `` elements lex as one word). Readonly assignment and circular namerefs abandon the line. See [Builtins](foundations/builtins.md#declaration-builtins-and-variable-scope).
 * **Fix**: Arithmetic follows bash's grammar and error model. New tokenizer + precedence-climbing evaluator (`interpreter/arithmetic.rs`): comma lists, chained/compound assignment, `**` right-assoc, `base#n` up to base 64, `noeval` short-circuit. `$((1/0))`, syntax errors and bad subscripts now print bash's message and abort the rest of the line (status 1) instead of yielding 0; `((...))` and `let` return 1. `((z <<= 65))` is read as raw text, not a heredoc. Bounds unchanged (`MAX_ARITHMETIC_DEPTH`, fuel; TM-DOS-026). See [Parser](foundations/parser.md#arithmetic-expressions).
 * **Fix**: Named file descriptors follow bash. `{var}>file` (and `<`, `>>`, `<>`, `<<<`, `<<`, `>&N`, `<&N`) allocates the lowest free fd >= 10 into `var` (local, array element; readonly fails) on any command, simple or compound, and the fd stays open as bash never undoes `{var}` redirections; `{var}>&-` closes it and a closed fd is reused. `>&N`/`<&N` to a closed fd is `Bad file descriptor` (status 1), a dup to a word is `ambiguous redirect`. The lexer accepts multi-digit fds (`10>x`), `<>` and `N<<<w`; `exec` applies its redirects in order and no longer re-applies them. Descriptors stay virtual per interpreter (no host fds); `cmd {v}>f` in a loop is capped by `max_file_descriptors` (TM-DOS-063 tests updated: a prior `$v` value is ignored). Gaps in [Limitations](operations/limitations.md) ("Named fds / `<>`").
+* **Fix**: xargs runs its command with stdin at EOF (`printf '' | xargs wc -l` prints 0); an empty pipe now reaches compound commands and functions as stdin at EOF; `printf %q` leaves printable non-ASCII unescaped under UTF-8.
 
 ## 2026-10-06