diff --git a/crates/deno_task_shell/src/grammar.pest b/crates/deno_task_shell/src/grammar.pest
index 8a98850..59efe11 100644
--- a/crates/deno_task_shell/src/grammar.pest
+++ b/crates/deno_task_shell/src/grammar.pest
@@ -11,6 +11,7 @@ UNQUOTED_PENDING_WORD = ${
     (TILDE_PREFIX ~ (!(OPERATOR | WHITESPACE | NEWLINE) ~ (
         EXIT_STATUS | 
         UNQUOTED_ESCAPE_CHAR | 
+        ARITHMETIC_EXPRESSION |
         SUB_COMMAND | 
         ("$" ~ "{" ~ VARIABLE ~ "}" | "$" ~ VARIABLE) | 
         UNQUOTED_CHAR | 
@@ -20,6 +21,7 @@ UNQUOTED_PENDING_WORD = ${
     (!(OPERATOR | WHITESPACE | NEWLINE) ~ (
         EXIT_STATUS | 
         UNQUOTED_ESCAPE_CHAR | 
+        ARITHMETIC_EXPRESSION |
         SUB_COMMAND | 
         ("$" ~ "{" ~ VARIABLE ~ "}" | "$" ~ VARIABLE) | 
         UNQUOTED_CHAR | 
@@ -148,7 +150,7 @@ command = !{
 
 compound_command = {
     brace_group |
-    subshell |
+    // subshell |
     for_clause |
     case_clause |
     if_clause |
@@ -156,7 +158,16 @@ compound_command = {
     until_clause
 }
 
-subshell = !{ "(" ~ compound_list ~ ")" }
+ARITHMETIC_EXPRESSION = { "$(" ~ "(" ~ arithmetic_expr ~  ")" ~ ")" }
+
+arithmetic_expr = { arithmetic_term ~ (add_op ~ arithmetic_term)* }
+arithmetic_term = { arithmetic_factor ~ (mul_op ~ arithmetic_factor)* }
+arithmetic_factor = { number | "(" ~ arithmetic_expr ~ ")" }
+number = @{ ASCII_DIGIT+ }
+add_op = { "+" | "-" }
+mul_op = { "*" | "/" }
+
+// subshell = !{ "(" ~ compound_list ~ ")" }
 compound_list = !{ (newline_list? ~ term ~ separator?)+ }
 term = !{ and_or ~ (separator ~ and_or)* }
 
diff --git a/crates/deno_task_shell/src/parser.rs b/crates/deno_task_shell/src/parser.rs
index 16f3c31..7d542a9 100644
--- a/crates/deno_task_shell/src/parser.rs
+++ b/crates/deno_task_shell/src/parser.rs
@@ -111,7 +111,7 @@ pub struct BooleanList {
 
 #[cfg_attr(feature = "serialization", derive(serde::Serialize))]
 #[cfg_attr(feature = "serialization", serde(rename_all = "camelCase"))]
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Error)]
+#[derive(Debug, Clone, PartialEq, Eq, Error)]
 pub enum PipeSequenceOperator {
   #[error("Stdout pipe operator")]
   Stdout,
@@ -374,6 +374,8 @@ pub enum WordPart {
   Variable(String),
   #[error("Invalid command")]
   Command(SequentialList),
+  #[error("Invalid arithmetic expression")]
+  Arithmetic(ArithmeticExpr),
   #[error("Invalid quoted string")]
   Quoted(Vec<WordPart>),
   #[error("Invalid tilde prefix")]
@@ -774,7 +776,7 @@ fn parse_compound_command(pair: Pair<Rule>) -> Result<Command> {
     Rule::brace_group => {
       Err(miette!("Unsupported compound command brace_group"))
     }
-    Rule::subshell => parse_subshell(inner),
+    // Rule::subshell => parse_subshell(inner),
     Rule::for_clause => Err(miette!("Unsupported compound command for_clause")),
     Rule::case_clause => {
       Err(miette!("Unsupported compound command case_clause"))
@@ -1085,6 +1087,11 @@ fn parse_word(pair: Pair<Rule>) -> Result<Word> {
             let tilde_prefix = parse_tilde_prefix(part)?;
             parts.push(tilde_prefix);
           }
+          Rule::ARITHMETIC_EXPRESSION => {
+            let expr = part.into_inner().next().unwrap();
+            let result = parse_arithmetic_expression(expr).unwrap();
+            parts.push(WordPart::Arithmetic(result));
+          }
           _ => {
             return Err(miette!(
               "Unexpected rule in UNQUOTED_PENDING_WORD: {:?}",
@@ -1173,6 +1180,7 @@ fn parse_quoted_word(pair: Pair<Rule>) -> Result<WordPart> {
         match part.as_rule() {
           Rule::EXIT_STATUS => parts.push(WordPart::Text("$?".to_string())),
           Rule::QUOTED_ESCAPE_CHAR => {
+            println!("QUOTED_ESCAPE_CHAR: {:?}", part.as_str());
             if let Some(WordPart::Text(ref mut s)) = parts.last_mut() {
               s.push_str(part.as_str());
             } else {
@@ -1353,6 +1361,68 @@ fn parse_io_file(pair: Pair<Rule>) -> Result<(RedirectOp, IoFile)> {
   Ok((redirect_op, io_file))
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ArithmeticExpr {
+    Number(i64),
+    Variable(String),
+    Add(Box<ArithmeticExpr>, Box<ArithmeticExpr>),
+    Subtract(Box<ArithmeticExpr>, Box<ArithmeticExpr>),
+    Multiply(Box<ArithmeticExpr>, Box<ArithmeticExpr>),
+    Divide(Box<ArithmeticExpr>, Box<ArithmeticExpr>),
+}
+
+fn parse_arithmetic_expression(expr: Pair<Rule>) -> Result<ArithmeticExpr, String> {
+    println!("parse_arithmetic_expression: {:?}", expr.as_rule());
+    match expr.as_rule() {
+        Rule::arithmetic_expr => parse_add_sub(expr.into_inner()),
+        // Rule::arithmetic_term => parse_mul_div(expr.into_inner()),
+        // Rule::arithmetic_factor => parse_factor(expr.into_inner()),
+        _ => Err(format!("Unexpected rule: {:?}", expr.as_rule())),
+    }
+}
+
+fn parse_add_sub(mut pairs: pest::iterators::Pairs<Rule>) -> Result<ArithmeticExpr, String> {
+    let mut expr = parse_mul_div(pairs.next().unwrap())?;
+    while let Some(op) = pairs.next() {
+        let rhs = parse_mul_div(pairs.next().unwrap())?;
+        expr = match op.as_str() {
+            "+" => ArithmeticExpr::Add(Box::new(expr), Box::new(rhs)),
+            "-" => ArithmeticExpr::Subtract(Box::new(expr), Box::new(rhs)),
+            _ => return Err(format!("Invalid operator: {}", op.as_str())),
+        };
+    }
+    Ok(expr)
+}
+
+fn parse_mul_div(pair: Pair<Rule>) -> Result<ArithmeticExpr, String> {
+    match pair.as_rule() {
+        Rule::arithmetic_term => {
+            let mut pairs = pair.into_inner();
+            let mut expr = parse_factor(pairs.next().unwrap())?;
+            while let Some(op) = pairs.next() {
+                let rhs = parse_factor(pairs.next().unwrap())?;
+                expr = match op.as_str() {
+                    "*" => ArithmeticExpr::Multiply(Box::new(expr), Box::new(rhs)),
+                    "/" => ArithmeticExpr::Divide(Box::new(expr), Box::new(rhs)),
+                    _ => return Err(format!("Invalid operator: {}", op.as_str())),
+                };
+            }
+            Ok(expr)
+        }
+        _ => Err(format!("Unexpected rule: {:?}", pair.as_rule())),
+    }
+}
+
+fn parse_factor(pair: Pair<Rule>) -> Result<ArithmeticExpr, String> {
+    println!("parse_factor: {:?}", pair.as_rule());
+    match pair.as_rule() {
+        Rule::number => pair.as_str().parse::<i64>().map(ArithmeticExpr::Number).map_err(|e| e.to_string()),
+        Rule::arithmetic_expr => parse_add_sub(pair.into_inner()),
+        Rule::arithmetic_factor => parse_factor(pair.into_inner()),
+        _ => Err(format!("Unexpected rule: {:?}", pair.as_rule())),
+    }
+}
+
 #[cfg(test)]
 mod test {
   use super::*;
diff --git a/crates/deno_task_shell/src/shell/execute.rs b/crates/deno_task_shell/src/shell/execute.rs
index 13de4a4..6e175a7 100644
--- a/crates/deno_task_shell/src/shell/execute.rs
+++ b/crates/deno_task_shell/src/shell/execute.rs
@@ -12,6 +12,7 @@ use thiserror::Error;
 use tokio::task::JoinHandle;
 use tokio_util::sync::CancellationToken;
 
+use crate::parser::ArithmeticExpr;
 use crate::parser::BinaryOp;
 use crate::parser::Condition;
 use crate::parser::ConditionInner;
@@ -882,6 +883,8 @@ pub enum EvaluateWordTextError {
   NoFilesMatched { pattern: String },
   #[error("Failed to get home directory")]
   FailedToGetHomeDirectory(anyhow::Error),
+  #[error("Arithmetic error: {0}")]
+  ArithmeticError(String),
 }
 
 impl EvaluateWordTextError {
@@ -1041,6 +1044,11 @@ fn evaluate_word_parts(
             )
             .await,
           ),
+          WordPart::Arithmetic(expr) => {
+            let text = evaluate_arithmetic_expression(expr, &state).map_err(|e| EvaluateWordTextError::ArithmeticError(e.to_string()))?;
+            current_text.push(TextPart::Text(text.to_string()));
+            continue;
+          }
           WordPart::Quoted(parts) => {
             let text = evaluate_word_parts_inner(
               parts,
@@ -1125,6 +1133,42 @@ fn evaluate_word_parts(
   evaluate_word_parts_inner(parts, false, state, stdin, stderr)
 }
 
+fn evaluate_arithmetic_expression(expr: ArithmeticExpr, state: &ShellState) -> Result<i64, String> {
+    match expr {
+        ArithmeticExpr::Number(n) => Ok(n),
+        ArithmeticExpr::Variable(var) => {
+            state.get_var(&var)
+                .and_then(|v| v.parse::<i64>().ok())
+                .ok_or_else(|| format!("Variable '{}' not found or not a valid integer", var))
+        },
+        ArithmeticExpr::Add(left, right) => {
+            let l = evaluate_arithmetic_expression(*left, state)?;
+            let r = evaluate_arithmetic_expression(*right, state)?;
+            Ok(l + r)
+        },
+        ArithmeticExpr::Subtract(left, right) => {
+            let l = evaluate_arithmetic_expression(*left, state)?;
+            let r = evaluate_arithmetic_expression(*right, state)?;
+            Ok(l - r)
+        },
+        ArithmeticExpr::Multiply(left, right) => {
+            let l = evaluate_arithmetic_expression(*left, state)?;
+            let r = evaluate_arithmetic_expression(*right, state)?;
+            Ok(l * r)
+        },
+        ArithmeticExpr::Divide(left, right) => {
+            let l = evaluate_arithmetic_expression(*left, state)?;
+            let r = evaluate_arithmetic_expression(*right, state)?;
+            if r == 0 {
+                Err("Division by zero".to_string())
+            } else {
+                Ok(l / r)
+            }
+        },
+    }
+
+}
+
 async fn evaluate_command_substitution(
   list: SequentialList,
   state: &ShellState,