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fix(interpreter): special params $0, $-, BASH_SUBSHELL, positional slices #2586

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Merged
chaliy merged 1 commit into from
Oct 7, 2026
Merged

fix(interpreter): special params $0, $-, BASH_SUBSHELL, positional slices #2586

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14 changes: 8 additions & 6 deletions crates/bashkit/src/builtins/read.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -213,15 +213,13 @@ impl Builtin for Read {
let mut fields: Vec<ReadField<'_>> = Vec::new();
let mut field_start = 0usize;
let mut i = 0usize;
let mut last_delim_was_non_ws = false;

while i < line.len() {
let mut iter = line[i..].char_indices();
let (_, ch) = iter.next().expect("valid char boundary");
let ch_len = ch.len_utf8();
if !ifs.contains(ch) {
i += ch_len;
last_delim_was_non_ws = false;
continue;
}

Expand All @@ -241,7 +239,6 @@ impl Builtin for Read {
}
}
field_start = i;
last_delim_was_non_ws = true;
} else {
let pushed_field = field_start != i;
if pushed_field {
Expand Down Expand Up @@ -281,11 +278,12 @@ impl Builtin for Read {
}

field_start = i;
last_delim_was_non_ws = false;
}
}

if field_start < line.len() || last_delim_was_non_ws {
// A single trailing delimiter ends the last field; it does
// not start an empty one (`a,b,` is two fields).
if field_start < line.len() {
fields.push(ReadField {
text: &line[field_start..],
start: field_start,
Expand Down Expand Up @@ -331,7 +329,11 @@ impl Builtin for Read {
if is_internal_variable(var_name) {
continue;
}
let value = if i == var_names.len() - 1 {
let value = if i == var_names.len() - 1 && words.len() == i + 1 {
// Only one field left: it is the value, without the
// delimiter that ended it (`IFS=, read x y <<< a,b,` gives `b`).
unprotect(words[i].text)
} else if i == var_names.len() - 1 {
// Bash gives the final variable the unsplit remaining input,
// then strips trailing IFS whitespace. Preserve original
// separators without keeping whitespace Bash trims.
Expand Down
50 changes: 50 additions & 0 deletions crates/bashkit/src/interpreter/expansion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -404,6 +404,19 @@ impl Interpreter {
Self::append_expansion_for_word(&mut result, word, &index_strs.join(" "));
}
}
WordPart::Substring {
name,
offset,
length,
} if name == "@" || name == "*" => {
let items = self.positional_slice(offset, length.as_deref());
let sep = if name == "*" {
self.get_ifs_separator()
} else {
" ".to_string()
};
Self::append_expansion_for_word(&mut result, word, &items.join(&sep));
}
WordPart::Substring {
name,
offset,
Expand Down Expand Up @@ -1389,11 +1402,48 @@ impl Interpreter {
}
(name, out)
}
WordPart::Substring {
name,
offset,
length,
} if name == "@" || name == "*" => {
let items = self.positional_slice(offset, length.as_deref());
(name, items)
}
_ => return None,
};
Some((results, name == "*" || name.ends_with("[*]")))
}

/// `${@:offset:length}`: positional parameters counted from `$0`
/// (offset 0 includes it); a negative offset counts back from the last.
fn positional_slice(&mut self, offset: &str, length: Option<&str>) -> Vec<String> {
let positional = self
.call_stack
.last()
.map(|f| f.positional.clone())
.unwrap_or_default();
let mut all = Vec::with_capacity(positional.len() + 1);
all.push(self.expand_variable("0"));
all.extend(positional);
let off = self.evaluate_arithmetic(offset);
let start = if off < 0 {
let back = usize::try_from(off.unsigned_abs()).unwrap_or(usize::MAX);
match all.len().checked_sub(back) {
Some(s) => s,
None => return Vec::new(),
}
} else {
usize::try_from(off).unwrap_or(usize::MAX).min(all.len())
};
let mut items: Vec<String> = all.into_iter().skip(start).collect();
if let Some(len) = length {
let n = self.evaluate_arithmetic(len);
items.truncate(usize::try_from(n.max(0)).unwrap_or(usize::MAX));
}
items
}

fn is_elementwise_op(operator: &ParameterOp) -> bool {
matches!(
operator,
Expand Down
75 changes: 61 additions & 14 deletions crates/bashkit/src/interpreter/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -992,6 +992,9 @@ struct CallFrame {
local_assoc_arrays: HashMap<String, Option<HashMap<String, String>>>,
/// Positional parameters ($1, $2, etc.)
positional: Vec<String>,
/// A function or `source` frame: `$0` comes from the nearest frame below
/// it that is not (the script or shell), as in bash.
keeps_arg0: bool,
}

/// A snapshot of shell state (variables, env, cwd, options).
Expand Down Expand Up @@ -1333,6 +1336,7 @@ struct SubshellSnapshot {
getopts_char_idx: usize,
last_bg_pid: Option<String>,
seconds_base: (crate::time_compat::Instant, i64),
bash_subshell: u32,
}

/// Interpreter state.
Expand Down Expand Up @@ -1425,6 +1429,8 @@ pub struct Interpreter {
builtin_stdout_pipe: Option<Arc<pipe::Pipe>>,
/// Input pipe handed to a streaming filter's `Context` (taken at dispatch).
builtin_stdin_pipe: Option<Arc<pipe::Pipe>>,
/// `$BASH_SUBSHELL`: subshell nesting (`( )`, `$( )`, pipeline stages, jobs).
bash_subshell: u32,
/// Position within the current argument while `getopts` walks a clustered
/// short-option group (e.g. `-abc`). Interpreter-internal working state for
/// `execute_getopts`; `0` means "at the start of the next option group".
Expand Down Expand Up @@ -2002,6 +2008,7 @@ impl Interpreter {
stream_stdout_command: None,
builtin_stdout_pipe: None,
builtin_stdin_pipe: None,
bash_subshell: 0,
getopts_char_idx: 0,
last_bg_pid: None,
output_callback: None,
Expand Down Expand Up @@ -2160,6 +2167,7 @@ impl Interpreter {
stream_stdout_command: None,
builtin_stdout_pipe: None,
builtin_stdin_pipe: None,
bash_subshell: self.bash_subshell + 1,
getopts_char_idx: self.getopts_char_idx,
last_bg_pid: self.last_bg_pid.clone(),
output_callback: None,
Expand Down Expand Up @@ -2512,6 +2520,7 @@ impl Interpreter {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional,
keeps_arg0: false,
});
}

Expand Down Expand Up @@ -3525,6 +3534,7 @@ impl Interpreter {
// bump; only mutations inside the subshell pay a clone.
let snap = self.snapshot_subshell_state();
let saved_call_stack = self.call_stack.clone();
self.bash_subshell += 1;
let saved_exit = self.last_exit_code;
let saved_coproc = self.coproc_buffers.clone();

Expand Down Expand Up @@ -5357,6 +5367,8 @@ impl Interpreter {
}
self.child_shell_depth += 1;
let child_snapshot = self.snapshot_subshell_state();
// A new shell starts at subshell level 0.
self.bash_subshell = 0;
self.reset_state_for_child_shell();

// Push call frame, apply options, execute, restore, pop
Expand All @@ -5366,6 +5378,7 @@ impl Interpreter {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: positional_args,
keeps_arg0: false,
});

let mut saved_opt_names: HashSet<&'static str> = HashSet::new();
Expand Down Expand Up @@ -5909,6 +5922,14 @@ impl Interpreter {
let write_end = pipe::WriteEnd(Arc::clone(&pipe));
let read_end = input.take().map(pipe::ReadEnd);
let command = command.clone();
if matches!(
command,
Command::Simple(_) | Command::Compound(CompoundCommand::Subshell(_), _)
) {
// Simple-command stages do not count as a subshell level; a
// `( )` stage counts itself once.
child.bash_subshell = self.bash_subshell;
}
stages.push(Box::pin(async move {
let _read_end = read_end;
if let Command::Simple(simple) = &command
Expand Down Expand Up @@ -6073,6 +6094,17 @@ impl Interpreter {
self.coproc_buffers.clone(),
)
});
// bash counts compound stages, not simple commands (`echo
// $BASH_SUBSHELL | cat` prints 0, `{ echo $BASH_SUBSHELL; } | cat` 1).
// A `( )` stage reuses the stage fork, so it is counted once.
if subshell
&& !matches!(
command,
Command::Simple(_) | Command::Compound(CompoundCommand::Subshell(_), _)
)
{
self.bash_subshell += 1;
}
let mut scope = PipelineStageScope {
saved,
prev_pipeline_stdin: None,
Expand Down Expand Up @@ -8079,6 +8111,7 @@ impl Interpreter {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: args.to_vec(),
keeps_arg0: false,
}];

// Set up BASH_SOURCE for the subprocess
Expand Down Expand Up @@ -8221,6 +8254,7 @@ impl Interpreter {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: source_args,
keeps_arg0: true,
});
} else if let Some(frame) = self.call_stack.last_mut() {
frame.positional = source_args;
Expand Down Expand Up @@ -8624,6 +8658,7 @@ impl Interpreter {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: args,
keeps_arg0: true,
});

// Set FUNCNAME array from call stack (index 0 = current, 1 = caller, ...)
Expand Down Expand Up @@ -10077,10 +10112,9 @@ impl Interpreter {
match effect {
builtins::BuiltinSideEffect::SetArray { name, elements } => {
let mut arr = HashMap::new();
// Empty fields are elements too (`IFS=, read -ra a <<< 'a,,b'`).
for (i, word) in elements.iter().enumerate() {
if !word.is_empty() {
arr.insert(i, word.clone());
}
arr.insert(i, word.clone());
}
self.insert_array_checked(name.clone(), arr);
}
Expand Down Expand Up @@ -10116,6 +10150,7 @@ impl Interpreter {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: new_positional.clone(),
keeps_arg0: false,
});
}
}
Expand Down Expand Up @@ -10207,6 +10242,7 @@ impl Interpreter {
getopts_char_idx: self.getopts_char_idx,
last_bg_pid: self.last_bg_pid.clone(),
seconds_base: self.seconds_base,
bash_subshell: self.bash_subshell,
}
}

Expand All @@ -10221,6 +10257,7 @@ impl Interpreter {
self.getopts_char_idx = snap.getopts_char_idx;
self.last_bg_pid = snap.last_bg_pid;
self.seconds_base = snap.seconds_base;
self.bash_subshell = snap.bash_subshell;
}

/// Perform the redirections of a null command (no command word) and
Expand Down Expand Up @@ -10364,6 +10401,7 @@ impl Interpreter {
// Command substitution runs in a subshell: snapshot all
// mutable state so mutations don't leak to the parent.
let snapshot = self.snapshot_subshell_state();
self.bash_subshell += 1;
// THREAT[TM-DOS-111]: Expansion happens before top-level output caps,
// so reserve every byte before growing the substitution buffer.
let mut stdout = BudgetedString::new(Some(&self.execution_budget))?;
Expand Down Expand Up @@ -11214,16 +11252,17 @@ impl Interpreter {
"-" => {
// $- - Current option flags as a string
// Build from SHOPT_* variables
// In bash's order; `h` (hashall) and `B` (braceexpand) are
// on by default and cannot be turned off here.
let mut flags = String::new();
for opt in ['e', 'x', 'u', 'f', 'n', 'v', 'a', 'b', 'h', 'm'] {
let opt_name = format!("SHOPT_{}", opt);
if self
.scoped
.variables
.get(&opt_name)
.map(|v| v == "1")
.unwrap_or(false)
{
for opt in ['a', 'b', 'e', 'f', 'h', 'm', 'n', 'u', 'v', 'x', 'B', 'C'] {
let on = matches!(opt, 'h' | 'B')
|| self
.scoped
.variables
.get(&format!("SHOPT_{opt}"))
.is_some_and(|v| v == "1");
if on {
flags.push(opt);
}
}
Expand Down Expand Up @@ -11267,6 +11306,9 @@ impl Interpreter {
"BASH_VERSION" => {
return COMPAT_BASH_VERSION.to_string();
}
"BASH_SUBSHELL" => {
return self.bash_subshell.to_string();
}
"SECONDS" => {
let (start, base) = self.seconds_base;
let elapsed = i64::try_from(start.elapsed().as_secs()).unwrap_or(i64::MAX);
Expand All @@ -11278,8 +11320,9 @@ impl Interpreter {
// Check for numeric positional parameter ($1, $2, etc.)
if let Ok(n) = name.parse::<usize>() {
if n == 0 {
// $0 is the script/function name
if let Some(frame) = self.call_stack.last() {
// $0 is the script/shell name; functions and `source`
// do not change it.
if let Some(frame) = self.call_stack.iter().rev().find(|f| !f.keeps_arg0) {
return frame.name.clone();
}
return Self::DEFAULT_ARG0.to_string();
Expand Down Expand Up @@ -11519,6 +11562,7 @@ mod tests {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: vec!["x".to_string(); 6000],
keeps_arg0: false,
});

let value = interp.resolve_param_expansion_name("@").1;
Expand Down Expand Up @@ -11636,6 +11680,7 @@ mod tests {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: Vec::new(),
keeps_arg0: false,
});
let baseline_call_stack_len = interp.call_stack.len();
let baseline_bash_source_len = interp.bash_source_stack.len();
Expand All @@ -11647,6 +11692,7 @@ mod tests {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: Vec::new(),
keeps_arg0: false,
});
interp.bash_source_stack.push("script.sh".to_string());

Expand Down Expand Up @@ -11815,6 +11861,7 @@ mod tests {
local_arrays: HashMap::new(),
local_assoc_arrays: HashMap::new(),
positional: Vec::new(),
keeps_arg0: false,
});
interp
.memory_budget
Expand Down
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