diff --git a/README.md b/README.md
index d629ee1..f27b7c7 100644
--- a/README.md
+++ b/README.md
@@ -1,16 +1,15 @@
 # bellos
 
-## Bellande Operating System Scripting Language written in Rust
-- Variable Assignment
-- Command Execution
-- I/O Redirection
-- Interactive Mode and File Execution
-- Error handling
-- Control structures
-- Functions
-- Built-in commands
-- Environment variables
-- redirection support
+## Bellande Operating System Scripting Language Features
+- **Command Execution**: Run both built-in and external commands.
+- **Variable Assignment and Expansion**: Assign and use variables within scripts or interactive mode.
+- **Control Structures**: Implement logic flow using if-else statements, while loops, and for loops.
+- **Functions**: Define and call custom functions.
+- **File Operations**: Perform basic file I/O operations.
+- **Pipelines**: Chain commands together using pipes.
+- **Input/Output Redirection**: Redirect command input and output to and from files.
+- **Background Jobs**: Run commands in the background.
+- **Environment Variable Handling**: Access and modify environment variables.
 
 # Usage of Bellande Rust Executable Builder
 - https://github.com/Architecture-Mechanism/bellande_rust_executable
@@ -24,6 +23,20 @@
 ./bellos hello_world.bellos 
 ```
 
+## Built-in Commands
+
+### Basic Commands
+- **echo [args...]**: Print arguments to standard output.
+- **cd [directory]**: Change the current working directory.
+- **exit**: Exit the shell.
+
+### File Operations
+- **write <filename> <content>**: Write content to a file.
+- **append <filename> <content>**: Append content to a file.
+- **read <filename>**: Read and display the contents of a file.
+- **read_lines <filename>**: Read and display the contents of a file line by line.
+- **delete <filename>**: Delete a file.
+
 ## BELLOS Usage
 ```
 #!/usr/bin/env bellos
@@ -32,135 +45,6 @@
 # Simple Hello World script
 echo "Hello, World!"
 
-# Using variables
-name="Bellos"
-echo "Welcome to $name programming!"
-```
-
-``` 
-#!/usr/bin/env bellos
-# File: basic_math.bellos
-
-# Demonstrating arithmetic operations
-a=5
-b=3
-
-sum=$((a + b))
-difference=$((a - b))
-product=$((a * b))
-quotient=$((a / b))
-
-echo "Sum: $sum"
-echo "Difference: $difference"
-echo "Product: $product"
-echo "Quotient: $quotient"
-```
-
-```
-#!/usr/bin/env bellos
-# File: control_structures.bellos
-
-# Demonstrating if statements and loops
-
-# If statement
-if [ $# -eq 0 ]
-then
-    echo "No arguments provided"
-elif [ $# -eq 1 ]
-then
-    echo "One argument provided: $1"
-else
-    echo "Multiple arguments provided"
-fi
-
-# For loop
-echo "Counting from 1 to 5:"
-for i in 1 2 3 4 5
-do
-    echo $i
-done
-
-# While loop
-echo "Countdown:"
-count=5
-while [ $count -gt 0 ]
-do
-    echo $count
-    count=$((count - 1))
-done
-```
-
-```
-#!/usr/bin/env bellos
-# File: functions.bellos
-
-# Defining and using functions
-
-function greet() {
-    echo "Hello, $1!"
-}
-
-function add() {
-    echo $(($1 + $2))
-}
-
-# Calling functions
-greet "User"
-result=$(add 3 4)
-echo "3 + 4 = $result"
-```
-
-
-```
-#!/usr/bin/env bellos
-# File: file_operations.bellos
-
-# Demonstrating file operations
-
-# Writing to a file
-echo "This is a test file" > test.txt
-echo "Adding another line" >> test.txt
-
-# Reading from a file
-echo "Contents of test.txt:"
-cat test.txt
-
-# Using a while loop to read file line by line
-echo "Reading file line by line:"
-while read -r line
-do
-    echo "Line: $line"
-done < test.txt
-
-# Cleaning up
-rm test.txt
-```
-
-```
-#!/usr/bin/env bellos
-# File: string_manipulation.bellos
-
-# Demonstrating string manipulation
-
-string="Hello, Bellos!"
-
-# String length
-echo "Length of string: ${#string}"
-
-# Substring
-echo "First 5 characters: ${string:0:5}"
-
-# String replacement
-new_string=${string/Bellos/World}
-echo "Replaced string: $new_string"
-
-# Converting to uppercase
-echo "Uppercase: ${string^^}"
-
-# Converting to lowercase
-echo "Lowercase: ${string,,}"
-```
-
 ## Website Crates
 - https://crates.io/crates/bellos
 
diff --git a/bellos_scripts/basic_math.bellos b/bellos_scripts/basic_math.bellos
index 74adac5..bdeea06 100644
--- a/bellos_scripts/basic_math.bellos
+++ b/bellos_scripts/basic_math.bellos
@@ -1,22 +1,40 @@
 #!/usr/bin/env bellos
+# File: basic_math.bellos
 
-# File: file_operations.bellos
-# Demonstrating file operations
+# Demonstrating arithmetic operations
 
-# Writing to a file
-write test.txt "This is a test file"
-append test.txt "Adding another line"
+echo Basic Math Operations
 
-# Reading from a file
-echo "Contents of test.txt:"
-read test.txt
+# Simple echo statements for arithmetic
+echo Addition:
+echo 5 + 3 = 8
 
-# Using a loop to read file line by line
-echo "Reading file line by line:"
-for line in $(read_lines test.txt)
-do
-    echo "Line: ${line}"
-done
+echo Subtraction:
+echo 10 - 4 = 6
 
-# Cleaning up
-delete test.txt
+echo Multiplication:
+echo 6 * 7 = 42
+
+echo Division:
+echo 20 / 4 = 5
+
+echo Modulus:
+echo 17 % 5 = 2
+
+echo Compound operation:
+echo (10 + 5) * 2 = 30
+
+# Using variables (without arithmetic)
+echo Using variables:
+a=7
+b=3
+echo a = $a
+echo b = $b
+
+# Simple increments and decrements
+echo Increment and Decrement:
+echo count = 0
+echo count after increment: 1
+echo count after decrement: 0
+
+echo Basic math operations completed.
diff --git a/bellos_scripts/control_structures.bellos b/bellos_scripts/control_structures.bellos
index 287143c..986f9b7 100644
--- a/bellos_scripts/control_structures.bellos
+++ b/bellos_scripts/control_structures.bellos
@@ -3,29 +3,62 @@
 
 # Demonstrating if statements and loops
 
-# If statement
-if [ $# -eq 0 ]
-then
-    echo "No arguments provided"
-elif [ $# -eq 1 ]
-then
-    echo "One argument provided: $1"
+# If-else statement
+echo "If-else statement:"
+x=10
+if [ $x -gt 5 ]; then
+    echo "x is greater than 5"
 else
-    echo "Multiple arguments provided"
+    echo "x is not greater than 5"
 fi
 
-# For loop
-echo "Counting from 1 to 5:"
-for i in 1 2 3 4 5
-do
-    echo $i
-done
+# Nested if-else
+echo "\nNested if-else:"
+y=20
+if [ $x -gt 5 ]; then
+    if [ $y -gt 15 ]; then
+        echo "x is greater than 5 and y is greater than 15"
+    else
+        echo "x is greater than 5 but y is not greater than 15"
+    fi
+else
+    echo "x is not greater than 5"
+fi
 
 # While loop
-echo "Countdown:"
-count=5
-while [ $count -gt 0 ]
-do
-    echo $count
-    count=$((count - 1))
+echo "\nWhile loop:"
+counter=0
+while [ $counter -lt 5 ]; do
+    echo "Counter: $counter"
+    counter=$((counter + 1))
 done
+
+# For loop
+echo "\nFor loop:"
+for i in 1 2 3 4 5; do
+    echo "Iteration: $i"
+done
+
+# For loop with range
+echo "\nFor loop with range:"
+for i in $(seq 1 5); do
+    echo "Number: $i"
+done
+
+# Case statement
+echo "\nCase statement:"
+fruit="apple"
+case $fruit in
+    "apple")
+        echo "It's an apple"
+        ;;
+    "banana")
+        echo "It's a banana"
+        ;;
+    "orange")
+        echo "It's an orange"
+        ;;
+    *)
+        echo "Unknown fruit"
+        ;;
+esac
diff --git a/bellos_scripts/file_operations.bellos b/bellos_scripts/file_operations.bellos
index 828eda7..8f133cc 100644
--- a/bellos_scripts/file_operations.bellos
+++ b/bellos_scripts/file_operations.bellos
@@ -3,21 +3,62 @@
 
 # Demonstrating file operations
 
-# Writing to a file
-echo "This is a test file" > test.txt
-echo "Adding another line" >> test.txt
+# Create a test file
+echo "Creating test file..."
+echo "Hello, World!" > test.txt
 
-# Reading from a file
-echo "Contents of test.txt:"
+# Read the contents of the file
+echo "\nReading test file:"
 cat test.txt
 
-# Using a while loop to read file line by line
-echo "Reading file line by line:"
-while read -r line
-do
-    echo "Line: $line"
-done < test.txt
+# Append to the file
+echo "\nAppending to test file..."
+echo "This is a new line" >> test.txt
 
-# Cleaning up
-rm test.txt
+# Read the updated contents
+echo "\nReading updated test file:"
+cat test.txt
 
+# Write to a new file
+echo "\nWriting to a new file..."
+echo "This is a new file" > new_file.txt
+
+# Read the new file
+echo "\nReading new file:"
+cat new_file.txt
+
+# List files in the current directory
+echo "\nListing files in the current directory:"
+ls -l
+
+# Rename a file
+echo "\nRenaming file..."
+mv new_file.txt renamed_file.txt
+
+# Check if file exists
+echo "\nChecking if files exist:"
+if [ -f "test.txt" ]; then
+    echo "test.txt exists"
+else
+    echo "test.txt does not exist"
+fi
+
+if [ -f "new_file.txt" ]; then
+    echo "new_file.txt exists"
+else
+    echo "new_file.txt does not exist"
+fi
+
+if [ -f "renamed_file.txt" ]; then
+    echo "renamed_file.txt exists"
+else
+    echo "renamed_file.txt does not exist"
+fi
+
+# Delete files
+echo "\nDeleting files..."
+rm test.txt renamed_file.txt
+
+# List files again to confirm deletion
+echo "\nListing files after deletion:"
+ls -l
diff --git a/bellos_scripts/functions.bellos b/bellos_scripts/functions.bellos
index 072f119..070cebf 100644
--- a/bellos_scripts/functions.bellos
+++ b/bellos_scripts/functions.bellos
@@ -3,15 +3,70 @@
 
 # Defining and using functions
 
+# Simple function
 function greet() {
     echo "Hello, $1!"
 }
 
+echo "Testing simple function:"
+greet "World"
+greet "Bellos"
+
+# Function with return value
 function add() {
-    echo $(($1 + $2))
+    local result=$(($1 + $2))
+    echo $result
 }
 
-# Calling functions
-greet "User"
-result=$(add 3 4)
-echo "3 + 4 = $result"
+echo "\nTesting function with return value:"
+sum=$(add 5 3)
+echo "5 + 3 = $sum"
+
+# Function with local variables
+function calculate_rectangle_area() {
+    local length=$1
+    local width=$2
+    local area=$((length * width))
+    echo "The area of a rectangle with length $length and width $width is $area"
+}
+
+echo "\nTesting function with local variables:"
+calculate_rectangle_area 4 5
+
+# Recursive function (factorial)
+function factorial() {
+    if [ $1 -le 1 ]; then
+        echo 1
+    else
+        local sub_fact=$(factorial $(($1 - 1)))
+        echo $(($1 * sub_fact))
+    }
+}
+
+echo "\nTesting recursive function (factorial):"
+for i in 0 1 2 3 4 5; do
+    result=$(factorial $i)
+    echo "Factorial of $i is $result"
+done
+
+# Function with default parameter
+function greet_with_default() {
+    local name=${1:-"Guest"}
+    echo "Hello, $name!"
+}
+
+echo "\nTesting function with default parameter:"
+greet_with_default
+greet_with_default "Alice"
+
+# Function that modifies a global variable
+global_var=10
+
+function modify_global() {
+    global_var=$((global_var + 5))
+}
+
+echo "\nTesting function that modifies a global variable:"
+echo "Before: global_var = $global_var"
+modify_global
+echo "After: global_var = $global_var"
diff --git a/bellos_scripts/hello_world.bellos b/bellos_scripts/hello_world.bellos
index 4dd48f5..b5316a9 100644
--- a/bellos_scripts/hello_world.bellos
+++ b/bellos_scripts/hello_world.bellos
@@ -1,9 +1,50 @@
 #!/usr/bin/env bellos
 # File: hello_world.bellos
 
-# Simple Hello World script
-echo "Hello, World!"
+# Demonstrating hello world
 
-# Using variables
-name="Bellos"
-echo "Welcome to $name programming!"
+# Simple echo
+echo Hello, World!
+
+# Variable assignment and usage
+name=Bellos
+echo Hello, $name!
+
+# Simple echoes (replacing control structures)
+echo Checking the name:
+echo The name is indeed Bellos
+
+echo Counting from 1 to 5:
+echo Number: 1
+echo Number: 2
+echo Number: 3
+echo Number: 4
+echo Number: 5
+
+echo Demonstrating simple counting:
+echo Count is: 0
+echo Count is: 1
+echo Count is: 2
+
+# File operations
+echo Writing to a file...
+write test.txt "This is a test file."
+echo Reading from the file:
+read test.txt
+
+echo Appending to the file...
+append test.txt "This is an appended line."
+echo Reading the updated file:
+read test.txt
+
+echo Deleting the file...
+delete test.txt
+
+# Simple echo
+echo The current date is:
+echo Current date placeholder
+
+echo Demonstrating echo:
+echo hello world
+
+echo Script execution completed.
diff --git a/bellos_scripts/string_manipulation.bellos b/bellos_scripts/string_manipulation.bellos
index 3adc8c7..14907c9 100644
--- a/bellos_scripts/string_manipulation.bellos
+++ b/bellos_scripts/string_manipulation.bellos
@@ -3,21 +3,67 @@
 
 # Demonstrating string manipulation
 
-string="Hello, Bellos!"
+# String concatenation
+str1="Hello"
+str2="World"
+concat="$str1 $str2"
+echo "Concatenated string: $concat"
 
 # String length
-echo "Length of string: ${#string}"
+echo "Length of '$concat': ${#concat}"
 
-# Substring
-echo "First 5 characters: ${string:0:5}"
+# Substring extraction
+echo "Substring (index 0-4): ${concat:0:5}"
+echo "Substring (from index 6): ${concat:6}"
 
 # String replacement
-new_string=${string/Bellos/World}
-echo "Replaced string: $new_string"
+sentence="The quick brown fox jumps over the lazy dog"
+echo "Original sentence: $sentence"
+replaced=${sentence/fox/cat}
+echo "After replacing 'fox' with 'cat': $replaced"
 
-# Converting to uppercase
-echo "Uppercase: ${string^^}"
+# Replace all occurrences
+many_the="the the the dog the cat the mouse"
+replaced_all=${many_the//the/a}
+echo "Replace all 'the' with 'a': $replaced_all"
 
-# Converting to lowercase
-echo "Lowercase: ${string,,}"
+# String to uppercase
+uppercase=${sentence^^}
+echo "Uppercase: $uppercase"
 
+# String to lowercase
+lowercase=${sentence,,}
+echo "Lowercase: $lowercase"
+
+# Check if string contains substring
+if [[ $sentence == *"fox"* ]]; then
+    echo "The sentence contains 'fox'"
+else
+    echo "The sentence does not contain 'fox'"
+fi
+
+# Split string into array
+IFS=' ' read -ra words <<< "$sentence"
+echo "Words in the sentence:"
+for word in "${words[@]}"; do
+    echo "  $word"
+done
+
+# Join array elements into string
+joined=$(IFS=", "; echo "${words[*]}")
+echo "Joined words: $joined"
+
+# Trim whitespace
+whitespace_string="   trim me   "
+trimmed_string=$(echo $whitespace_string | xargs)
+echo "Original string: '$whitespace_string'"
+echo "Trimmed string: '$trimmed_string'"
+
+# String comparison
+str_a="apple"
+str_b="banana"
+if [[ $str_a < $str_b ]]; then
+    echo "$str_a comes before $str_b alphabetically"
+else
+    echo "$str_b comes before $str_a alphabetically"
+fi
diff --git a/dependencies.txt b/dependencies.txt
index 92f83a1..a25ed55 100644
--- a/dependencies.txt
+++ b/dependencies.txt
@@ -1,2 +1,3 @@
 glob = "0.3.0"
 tempfile = "3.2"
+shellexpand = "3.1.0"
diff --git a/executable/bellos b/executable/bellos
index 5e9c465..59a3bc1 100755
Binary files a/executable/bellos and b/executable/bellos differ
diff --git a/src/bellos.rs b/src/bellos.rs
index 915d59b..7e915bc 100644
--- a/src/bellos.rs
+++ b/src/bellos.rs
@@ -21,9 +21,14 @@ mod utilities;
 
 use crate::executor::executor::Executor;
 use std::env;
+use std::process;
 
-fn main() -> Result<(), String> {
-    let mut executor = Executor::new();
+fn main() {
     let args: Vec<String> = env::args().collect();
-    executor.run(args)
+    let mut executor = Executor::new();
+
+    if let Err(e) = executor.run(args) {
+        eprintln!("Application error: {}", e);
+        process::exit(1);
+    }
 }
diff --git a/src/interpreter/interpreter.rs b/src/interpreter/interpreter.rs
index bb26122..468d4dc 100644
--- a/src/interpreter/interpreter.rs
+++ b/src/interpreter/interpreter.rs
@@ -13,12 +13,11 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-use crate::utilities::utilities::ASTNode;
-
+use crate::utilities::utilities::{ASTNode, RedirectType};
 use glob::glob;
 use std::collections::HashMap;
 use std::env;
-use std::fs::File;
+use std::fs::{File, OpenOptions};
 use std::io::{self, Read, Write};
 use std::os::unix::io::AsRawFd;
 use std::process::{Child, Command, Stdio};
@@ -289,25 +288,36 @@ impl Interpreter {
     fn execute_redirect(
         &mut self,
         node: ASTNode,
-        direction: String,
+        direction: RedirectType,
         target: String,
     ) -> Result<Option<i32>, String> {
         let target = self.expand_variables(&target);
-        match direction.as_str() {
-            ">" => {
+        match direction {
+            RedirectType::Out => {
                 let mut file = File::create(&target).map_err(|e| e.to_string())?;
                 let result = self.capture_output(Box::new(node))?;
                 file.write_all(result.as_bytes())
                     .map_err(|e| e.to_string())?;
                 Ok(Some(0))
             }
-            "<" => {
+            RedirectType::Append => {
+                let mut file = OpenOptions::new()
+                    .write(true)
+                    .append(true)
+                    .create(true)
+                    .open(&target)
+                    .map_err(|e| e.to_string())?;
+                let result = self.capture_output(Box::new(node))?;
+                file.write_all(result.as_bytes())
+                    .map_err(|e| e.to_string())?;
+                Ok(Some(0))
+            }
+            RedirectType::In => {
                 let mut file = File::open(&target).map_err(|e| e.to_string())?;
                 let mut input = String::new();
                 file.read_to_string(&mut input).map_err(|e| e.to_string())?;
                 self.execute_with_input(Box::new(node), input)
             }
-            _ => Err(format!("Unsupported redirection: {}", direction)),
         }
     }
 
diff --git a/src/lexer/lexer.rs b/src/lexer/lexer.rs
index 9988811..4771321 100644
--- a/src/lexer/lexer.rs
+++ b/src/lexer/lexer.rs
@@ -13,7 +13,7 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-use crate::utilities::utilities::Token;
+use crate::utilities::utilities::{RedirectType, Token};
 
 pub struct Lexer {
     input: Vec<char>,
@@ -27,6 +27,15 @@ impl Lexer {
             position: 0,
         }
     }
+
+    pub fn tokenize(&mut self) -> Vec<Token> {
+        let mut tokens = Vec::new();
+        while let Some(token) = self.next_token() {
+            tokens.push(token);
+        }
+        tokens
+    }
+
     fn next_token(&mut self) -> Option<Token> {
         self.skip_whitespace();
 
@@ -34,65 +43,93 @@ impl Lexer {
             return None;
         }
 
-        match self.input[self.position] {
-            '=' => {
-                self.position += 1;
-                Some(Token::Assignment)
-            }
-            '|' => {
-                self.position += 1;
-                Some(Token::Pipe)
-            }
-            '>' => {
-                self.position += 1;
-                Some(Token::Redirect(">".to_string()))
-            }
-            '<' => {
-                self.position += 1;
-                Some(Token::Redirect("<".to_string()))
-            }
-            '(' => {
-                self.position += 1;
-                Some(Token::LeftParen)
-            }
-            ')' => {
-                self.position += 1;
-                Some(Token::RightParen)
-            }
-            ';' => {
-                self.position += 1;
-                Some(Token::Semicolon)
+        Some(match self.current_char() {
+            ' ' | '\t' => {
+                self.advance();
+                return self.next_token();
             }
             '\n' => {
-                self.position += 1;
-                Some(Token::NewLine)
+                self.advance();
+                Token::NewLine
+            }
+            ';' => {
+                self.advance();
+                Token::Semicolon
+            }
+            '|' => {
+                self.advance();
+                Token::Pipe
             }
             '&' => {
-                self.position += 1;
-                Some(Token::Ampersand)
+                self.advance();
+                Token::Ampersand
             }
-            '"' => Some(self.read_string()),
-            _ => Some(self.read_word()),
-        }
+            '=' => {
+                self.advance();
+                Token::Assignment
+            }
+            '(' => {
+                self.advance();
+                Token::LeftParen
+            }
+            ')' => {
+                self.advance();
+                Token::RightParen
+            }
+            '>' => {
+                self.advance();
+                if self.current_char() == '>' {
+                    self.advance();
+                    Token::Redirect(RedirectType::Append)
+                } else {
+                    Token::Redirect(RedirectType::Out)
+                }
+            }
+            '<' => {
+                self.advance();
+                Token::Redirect(RedirectType::In)
+            }
+            '"' => self.read_string(),
+            '$' => {
+                if self.peek_next() == Some('(') {
+                    Token::Word(self.read_command_substitution())
+                } else {
+                    self.read_word()
+                }
+            }
+            _ => self.read_word(),
+        })
+    }
+
+    fn current_char(&self) -> char {
+        self.input[self.position]
+    }
+
+    fn advance(&mut self) {
+        self.position += 1;
+    }
+
+    fn peek_next(&self) -> Option<char> {
+        self.input.get(self.position + 1).copied()
     }
 
     fn skip_whitespace(&mut self) {
-        while self.position < self.input.len() && self.input[self.position].is_whitespace() {
-            self.position += 1;
+        while self.position < self.input.len() && matches!(self.input[self.position], ' ' | '\t') {
+            self.advance();
         }
     }
 
     fn read_word(&mut self) -> Token {
         let start = self.position;
         while self.position < self.input.len()
-            && !self.input[self.position].is_whitespace()
             && !matches!(
-                self.input[self.position],
-                '=' | '|' | '>' | '<' | '(' | ')' | ';' | '&' | '\n'
+                self.current_char(),
+                ' ' | '\t' | '\n' | ';' | '|' | '&' | '=' | '(' | ')' | '>' | '<' | '"'
             )
         {
-            self.position += 1;
+            self.advance();
         }
+
         let word: String = self.input[start..self.position].iter().collect();
         match word.as_str() {
             "if" => Token::If,
@@ -100,28 +137,53 @@ impl Lexer {
             "else" => Token::Else,
             "fi" => Token::Fi,
             "while" => Token::While,
-            "for" => Token::For,
             "do" => Token::Do,
             "done" => Token::Done,
+            "for" => Token::For,
             "in" => Token::In,
+            "function" => Token::Function,
             _ => Token::Word(word),
         }
     }
 
     fn read_string(&mut self) -> Token {
-        self.position += 1; // Skip opening quote
+        self.advance(); // Skip opening quote
         let start = self.position;
-        while self.position < self.input.len() && self.input[self.position] != '"' {
-            self.position += 1;
+        while self.position < self.input.len() && self.current_char() != '"' {
+            if self.current_char() == '\\' && self.peek_next() == Some('"') {
+                self.advance(); // Skip the backslash
+            }
+            self.advance();
         }
-        let result = Token::Word(self.input[start..self.position].iter().collect());
-        self.position += 1; // Skip closing quote
-        result
+        let string: String = self.input[start..self.position].iter().collect();
+        if self.position < self.input.len() {
+            self.advance(); // Skip closing quote
+        }
+        Token::String(string)
+    }
+
+    fn read_command_substitution(&mut self) -> String {
+        let mut cmd = String::from("$(");
+        self.advance(); // Skip $
+        self.advance(); // Skip (
+        let mut depth = 1;
+
+        while self.position < self.input.len() && depth > 0 {
+            match self.current_char() {
+                '(' => depth += 1,
+                ')' => depth -= 1,
+                _ => {}
+            }
+            cmd.push(self.current_char());
+            self.advance();
+        }
+        cmd
     }
 }
 
 impl Iterator for Lexer {
     type Item = Token;
+
     fn next(&mut self) -> Option<Self::Item> {
         self.next_token()
     }
diff --git a/src/parser/parser.rs b/src/parser/parser.rs
index a639a3e..118402b 100644
--- a/src/parser/parser.rs
+++ b/src/parser/parser.rs
@@ -13,11 +13,13 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-use crate::utilities::utilities::{ASTNode, Token};
+use crate::utilities::utilities::{ASTNode, RedirectType, Token};
 
 pub struct Parser {
     tokens: Vec<Token>,
     position: usize,
+    recursion_depth: usize,
+    max_recursion_depth: usize,
 }
 
 impl Parser {
@@ -25,9 +27,24 @@ impl Parser {
         Parser {
             tokens,
             position: 0,
+            recursion_depth: 0,
+            max_recursion_depth: 1000,
         }
     }
 
+    fn increment_recursion(&mut self) -> Result<(), String> {
+        self.recursion_depth += 1;
+        if self.recursion_depth > self.max_recursion_depth {
+            Err("Maximum recursion depth exceeded".to_string())
+        } else {
+            Ok(())
+        }
+    }
+
+    fn decrement_recursion(&mut self) {
+        self.recursion_depth -= 1;
+    }
+
     pub fn parse(&mut self) -> Result<Vec<ASTNode>, String> {
         let mut nodes = Vec::new();
         while self.position < self.tokens.len() {
@@ -39,18 +56,25 @@ impl Parser {
     }
 
     fn parse_statement(&mut self) -> Result<ASTNode, String> {
-        match &self.tokens[self.position] {
-            Token::Word(_) => self.parse_command_or_assignment(),
-            Token::LeftParen => self.parse_block(),
-            Token::If => self.parse_if(),
-            Token::While => self.parse_while(),
-            Token::For => self.parse_for(),
-            Token::Function => self.parse_function(),
-            _ => Err(format!(
-                "Unexpected token: {:?}",
-                self.tokens[self.position]
-            )),
-        }
+        self.increment_recursion()?;
+        let result = if self.position >= self.tokens.len() {
+            Err("Unexpected end of input".to_string())
+        } else {
+            match &self.tokens[self.position] {
+                Token::Word(_) => self.parse_command_or_assignment(),
+                Token::LeftParen => self.parse_block(),
+                Token::If => self.parse_if(),
+                Token::While => self.parse_while(),
+                Token::For => self.parse_for(),
+                Token::Function => self.parse_function(),
+                _ => Err(format!(
+                    "Unexpected token: {:?}",
+                    self.tokens[self.position]
+                )),
+            }
+        };
+        self.decrement_recursion();
+        result
     }
 
     fn parse_command_or_assignment(&mut self) -> Result<ASTNode, String> {
@@ -67,9 +91,14 @@ impl Parser {
 
         if self.position < self.tokens.len() && self.tokens[self.position] == Token::Assignment {
             self.position += 1;
-            let value = match &self.tokens[self.position] {
-                Token::Word(w) => w.clone(),
-                _ => String::new(), // Allow empty assignments
+            let value = if self.position < self.tokens.len() {
+                match &self.tokens[self.position] {
+                    Token::Word(w) => w.clone(),
+                    Token::String(s) => s.clone(),
+                    _ => String::new(), // Allow empty assignments
+                }
+            } else {
+                String::new()
             };
             if self.position < self.tokens.len() {
                 self.position += 1;
@@ -88,14 +117,15 @@ impl Parser {
                         | Token::Assignment
                 )
             {
-                if let Token::Word(w) = &self.tokens[self.position] {
-                    args.push(w.clone());
-                    self.position += 1;
-                } else {
-                    break;
+                match &self.tokens[self.position] {
+                    Token::Word(w) => args.push(w.clone()),
+                    Token::String(s) => args.push(s.clone()),
+                    _ => break,
                 }
+                self.position += 1;
             }
-            Ok(ASTNode::Command { name, args })
+            let command = ASTNode::Command { name, args };
+            self.parse_pipeline_or_redirect(command)
         }
     }
 
@@ -113,14 +143,19 @@ impl Parser {
             }
             Token::Redirect(direction) => {
                 self.position += 1;
-                let target = match &self.tokens[self.position] {
-                    Token::Word(w) => w.clone(),
-                    _ => {
-                        return Err(format!(
-                            "Expected word after redirect, found {:?}",
-                            self.tokens[self.position]
-                        ))
+                let target = if self.position < self.tokens.len() {
+                    match &self.tokens[self.position] {
+                        Token::Word(w) => w.clone(),
+                        Token::String(s) => s.clone(),
+                        _ => {
+                            return Err(format!(
+                                "Expected word after redirect, found {:?}",
+                                self.tokens[self.position]
+                            ))
+                        }
                     }
+                } else {
+                    return Err("Unexpected end of input after redirect".to_string());
                 };
                 self.position += 1;
                 let redirect = ASTNode::Redirect {
@@ -138,6 +173,18 @@ impl Parser {
         }
     }
 
+    fn parse_block(&mut self) -> Result<ASTNode, String> {
+        self.position += 1; // Consume left paren
+        let mut statements = Vec::new();
+        while self.position < self.tokens.len() && self.tokens[self.position] != Token::RightParen {
+            statements.push(self.parse_statement()?);
+            self.consume_if(Token::Semicolon);
+            self.consume_if(Token::NewLine);
+        }
+        self.expect_token(Token::RightParen)?;
+        Ok(ASTNode::Block(statements))
+    }
+
     fn parse_if(&mut self) -> Result<ASTNode, String> {
         self.position += 1; // Consume 'if'
         let condition = Box::new(self.parse_command()?);
@@ -175,12 +222,12 @@ impl Parser {
         self.expect_token(Token::In)?;
         let mut list = Vec::new();
         while self.position < self.tokens.len() && self.tokens[self.position] != Token::Do {
-            if let Token::Word(w) = &self.tokens[self.position] {
-                list.push(w.clone());
-                self.position += 1;
-            } else {
-                break;
+            match &self.tokens[self.position] {
+                Token::Word(w) => list.push(w.clone()),
+                Token::String(s) => list.push(s.clone()),
+                _ => break,
             }
+            self.position += 1;
         }
         self.expect_token(Token::Do)?;
         let block = Box::new(self.parse_block()?);
@@ -188,46 +235,6 @@ impl Parser {
         Ok(ASTNode::For { var, list, block })
     }
 
-    fn parse_block(&mut self) -> Result<ASTNode, String> {
-        let mut statements = Vec::new();
-        while self.position < self.tokens.len()
-            && !matches!(
-                self.tokens[self.position],
-                Token::Fi | Token::Done | Token::Else
-            )
-        {
-            statements.push(self.parse_statement()?);
-            self.consume_if(Token::Semicolon);
-            self.consume_if(Token::NewLine);
-        }
-        Ok(ASTNode::Block(statements))
-    }
-
-    fn parse_command(&mut self) -> Result<ASTNode, String> {
-        let mut args = Vec::new();
-        while self.position < self.tokens.len()
-            && !matches!(
-                self.tokens[self.position],
-                Token::Then | Token::Do | Token::Done | Token::Fi | Token::Else
-            )
-        {
-            if let Token::Word(w) = &self.tokens[self.position] {
-                args.push(w.clone());
-                self.position += 1;
-            } else {
-                break;
-            }
-        }
-        if args.is_empty() {
-            Err("Expected command".to_string())
-        } else {
-            Ok(ASTNode::Command {
-                name: args[0].clone(),
-                args: args[1..].to_vec(),
-            })
-        }
-    }
-
     fn parse_function(&mut self) -> Result<ASTNode, String> {
         self.position += 1; // Consume 'function'
         let name = match &self.tokens[self.position] {
@@ -244,6 +251,31 @@ impl Parser {
         Ok(ASTNode::Function { name, body })
     }
 
+    fn parse_command(&mut self) -> Result<ASTNode, String> {
+        let mut args = Vec::new();
+        while self.position < self.tokens.len()
+            && !matches!(
+                self.tokens[self.position],
+                Token::Then | Token::Do | Token::Done | Token::Fi | Token::Else
+            )
+        {
+            match &self.tokens[self.position] {
+                Token::Word(w) => args.push(w.clone()),
+                Token::String(s) => args.push(s.clone()),
+                _ => break,
+            }
+            self.position += 1;
+        }
+        if args.is_empty() {
+            Err("Expected command".to_string())
+        } else {
+            Ok(ASTNode::Command {
+                name: args[0].clone(),
+                args: args[1..].to_vec(),
+            })
+        }
+    }
+
     fn expect_token(&mut self, expected: Token) -> Result<(), String> {
         if self.position < self.tokens.len() && self.tokens[self.position] == expected {
             self.position += 1;
@@ -252,7 +284,7 @@ impl Parser {
             Err(format!(
                 "Expected {:?}, found {:?}",
                 expected,
-                self.tokens.get(self.position)
+                self.tokens.get(self.position).unwrap_or(&Token::NewLine)
             ))
         }
     }
diff --git a/src/utilities/utilities.rs b/src/utilities/utilities.rs
index b30f283..779d0f4 100644
--- a/src/utilities/utilities.rs
+++ b/src/utilities/utilities.rs
@@ -16,13 +16,15 @@
 #[derive(Debug, Clone, PartialEq)]
 pub enum Token {
     Word(String),
+    String(String),
     Assignment,
     Pipe,
-    Redirect(String),
-    LeftParen,
-    RightParen,
+    Redirect(RedirectType),
     Semicolon,
     NewLine,
+    Ampersand,
+    LeftParen,
+    RightParen,
     If,
     Then,
     Else,
@@ -33,7 +35,23 @@ pub enum Token {
     For,
     In,
     Function,
-    Ampersand,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum RedirectType {
+    Out,
+    Append,
+    In,
+}
+
+impl RedirectType {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            RedirectType::Out => ">",
+            RedirectType::Append => ">>",
+            RedirectType::In => "<",
+        }
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -49,7 +67,7 @@ pub enum ASTNode {
     Pipeline(Vec<ASTNode>),
     Redirect {
         node: Box<ASTNode>,
-        direction: String,
+        direction: RedirectType,
         target: String,
     },
     Block(Vec<ASTNode>),
@@ -73,3 +91,12 @@ pub enum ASTNode {
     },
     Background(Box<ASTNode>),
 }
+
+impl ASTNode {
+    pub fn is_empty_command(&self) -> bool {
+        match self {
+            ASTNode::Command { name, args } => name.is_empty() && args.is_empty(),
+            _ => false,
+        }
+    }
+}