diff --git a/crates/deno_task_shell/src/grammar.pest b/crates/deno_task_shell/src/grammar.pest
index 68657bf..6289e84 100644
--- a/crates/deno_task_shell/src/grammar.pest
+++ b/crates/deno_task_shell/src/grammar.pest
@@ -202,34 +202,33 @@ bitwise_or = { "|" }
 logical_and = { "&&" }
 logical_or = { "||" }
 
+unary_plus = { "+" }
+unary_minus = { "-" }
+logical_not = { "!" }
+bitwise_not = { "~" }
+increment = { "++" }
+decrement = { "--" }
+
 unary_arithmetic_expr = !{
     unary_pre_arithmetic_expr | unary_post_arithmetic_expr
 }
 
 unary_pre_arithmetic_expr = !{
-    (post_arithmetic_op | pre_arithmetic_op) ~ (parentheses_expr | VARIABLE | NUMBER)
+    pre_arithmetic_op ~ (parentheses_expr | VARIABLE | NUMBER)
 }
 
 unary_post_arithmetic_expr = !{
     (parentheses_expr | VARIABLE | NUMBER) ~ post_arithmetic_op
 }
 
-pre_arithmetic_op= _{
-    unary_plus | unary_minus | logical_not | bitwise_not
+pre_arithmetic_op= !{
+    increment | decrement | unary_plus | unary_minus | logical_not | bitwise_not
 }
 
-unary_plus = { "+" }
-unary_minus = { "-" }
-logical_not = { "!" }
-bitwise_not = { "~" }
-
 post_arithmetic_op = !{
     increment | decrement
 }
 
-increment = { "++" }
-decrement = { "--" }
-
 assignment_operator = _{
     assign | multiply_assign | divide_assign | modulo_assign | add_assign | subtract_assign |
     left_shift_assign | right_shift_assign | bitwise_and_assign | bitwise_xor_assign | bitwise_or_assign
diff --git a/crates/deno_task_shell/src/parser.rs b/crates/deno_task_shell/src/parser.rs
index 2e4fb0d..9a3cbf8 100644
--- a/crates/deno_task_shell/src/parser.rs
+++ b/crates/deno_task_shell/src/parser.rs
@@ -1469,9 +1469,9 @@ fn unary_pre_arithmetic_expr(pair: Pair<Rule>) -> Result<ArithmeticPart> {
       })
     }
     Rule::post_arithmetic_op => {
-      let op = parse_pre_arithmetic_op(first)?;
+      let op = parse_post_arithmetic_op(first)?;
       Ok(ArithmeticPart::UnaryArithmeticExpr {
-        operator: UnaryArithmeticOp::Pre(op),
+        operator: UnaryArithmeticOp::Post(op),
         operand: Box::new(operand),
       })
     }
@@ -1519,12 +1519,12 @@ fn parse_pre_arithmetic_op(pair: Pair<Rule>) -> Result<PreArithmeticOp> {
   match first.as_rule() {
     Rule::increment => Ok(PreArithmeticOp::Increment),
     Rule::decrement => Ok(PreArithmeticOp::Decrement),
-    Rule::add => Ok(PreArithmeticOp::Plus),
-    Rule::subtract => Ok(PreArithmeticOp::Minus),
+    Rule::unary_plus => Ok(PreArithmeticOp::Plus),
+    Rule::unary_minus => Ok(PreArithmeticOp::Minus),
     Rule::logical_not => Ok(PreArithmeticOp::LogicalNot),
     Rule::bitwise_not => Ok(PreArithmeticOp::BitwiseNot),
     _ => Err(miette!(
-      "Unexpected rule in post arithmetic operator: {:?}",
+      "Unexpected rule in pre arithmetic operator: {:?}",
       first.as_rule()
     )),
   }
diff --git a/crates/deno_task_shell/src/shell/types.rs b/crates/deno_task_shell/src/shell/types.rs
index 1ca905b..f8db925 100644
--- a/crates/deno_task_shell/src/shell/types.rs
+++ b/crates/deno_task_shell/src/shell/types.rs
@@ -636,17 +636,19 @@ impl ArithmeticResult {
         ArithmeticValue::Integer(val) => match operand {
           ArithmeticPart::Variable(name) => {
             let mut new_changes = self.changes.clone();
-            new_changes.push(EnvChange::SetShellVar(
-              name.to_string(),
-              match op_type {
-                PreArithmeticOp::Increment => (*val + 1).to_string(),
-                PreArithmeticOp::Decrement => (*val - 1).to_string(),
-                _ => todo!(
-                  "Unary arithmetic operation not implemented {:?}",
-                  op_type
-                ),
-              },
-            ));
+            if op_type == PreArithmeticOp::Increment
+              || op_type == PreArithmeticOp::Decrement
+            {
+              new_changes.push(EnvChange::SetShellVar(
+                name.to_string(),
+                match op_type {
+                  PreArithmeticOp::Increment => (*val + 1).to_string(),
+                  PreArithmeticOp::Decrement => (*val - 1).to_string(),
+                  _ => Err(miette!("No change to ENV need for: {}", self))?,
+                },
+              ));
+            }
+
             Ok(ArithmeticResult {
               value: match op_type {
                 PreArithmeticOp::Increment => {
@@ -655,10 +657,14 @@ impl ArithmeticResult {
                 PreArithmeticOp::Decrement => {
                   ArithmeticValue::Integer(*val - 1)
                 }
-                _ => todo!(
-                  "Unary arithmetic operation not implemented {:?}",
-                  op_type
-                ),
+                PreArithmeticOp::Plus => ArithmeticValue::Integer((*val).abs()),
+                PreArithmeticOp::Minus => {
+                  ArithmeticValue::Integer(-(*val).abs())
+                }
+                PreArithmeticOp::BitwiseNot => ArithmeticValue::Integer(!*val),
+                PreArithmeticOp::LogicalNot => {
+                  ArithmeticValue::Integer(if *val == 0 { 1 } else { 0 })
+                }
               },
               changes: new_changes,
             })
@@ -671,17 +677,19 @@ impl ArithmeticResult {
         ArithmeticValue::Float(val) => match operand {
           ArithmeticPart::Variable(name) => {
             let mut new_changes = self.changes.clone();
-            new_changes.push(EnvChange::SetShellVar(
-              name.to_string(),
-              match op_type {
-                PreArithmeticOp::Increment => (*val + 1.0).to_string(),
-                PreArithmeticOp::Decrement => (*val - 1.0).to_string(),
-                _ => todo!(
-                  "Unary arithmetic operation not implemented {:?}",
-                  op_type
-                ),
-              },
-            ));
+            if op_type == PreArithmeticOp::Increment
+              || op_type == PreArithmeticOp::Decrement
+            {
+              new_changes.push(EnvChange::SetShellVar(
+                name.to_string(),
+                match op_type {
+                  PreArithmeticOp::Increment => (*val + 1.0).to_string(),
+                  PreArithmeticOp::Decrement => (*val - 1.0).to_string(),
+                  _ => Err(miette!("No change to ENV need for: {}", self))?,
+                },
+              ));
+            }
+
             Ok(ArithmeticResult {
               value: match op_type {
                 PreArithmeticOp::Increment => {
@@ -690,10 +698,14 @@ impl ArithmeticResult {
                 PreArithmeticOp::Decrement => {
                   ArithmeticValue::Float(*val - 1.0)
                 }
-                _ => todo!(
-                  "Unary arithmetic operation not implemented {:?}",
-                  op_type
-                ),
+                PreArithmeticOp::Plus => ArithmeticValue::Float((*val).abs()),
+                PreArithmeticOp::Minus => ArithmeticValue::Float(-(*val).abs()),
+                PreArithmeticOp::BitwiseNot => {
+                  ArithmeticValue::Integer(!(*val as i64))
+                }
+                PreArithmeticOp::LogicalNot => {
+                  ArithmeticValue::Float(if *val == 0.0 { 1.0 } else { 0.0 })
+                }
               },
               changes: new_changes,
             })
diff --git a/crates/tests/src/lib.rs b/crates/tests/src/lib.rs
index a489b98..6c73b7e 100644
--- a/crates/tests/src/lib.rs
+++ b/crates/tests/src/lib.rs
@@ -904,6 +904,30 @@ async fn arithmetic() {
         .assert_stdout("0\n")
         .run()
         .await;
+
+    TestBuilder::new()
+        .command("echo $((a=1, +a))")
+        .assert_stdout("1\n")
+        .run()
+        .await;
+
+    TestBuilder::new()
+        .command("echo $((a=1, -a))")
+        .assert_stdout("-1\n")
+        .run()
+        .await;
+
+    TestBuilder::new()
+        .command("echo $((a=3, ~a))")
+        .assert_stdout("-4\n")
+        .run()
+        .await;
+
+    TestBuilder::new()
+        .command("echo $((a=0, !a))")
+        .assert_stdout("1\n")
+        .run()
+        .await;
 }
 
 #[tokio::test]