Bash Scripting Language Cheatsheet

Bash, short for “Bourne Again SHell,” is a powerful and widely used scripting language on Unix and Unix-like systems. It serves as a command processor, allowing users to interact with the operating system and automate tasks through scripts. Whether you’re a beginner or an experienced developer, having a cheatsheet handy can be incredibly useful for quick reference. In this blog post, we’ll provide a comprehensive Bash programming language cheatsheet to help you navigate the essentials.

1. Variables

# Declare a variable
variable_name="Hello, World!"

# Access variable value
echo $variable_name

# Concatenate strings
greeting="Hello"
name="John"
message="$greeting, $name!"
echo $message

2. Conditionals

# If statement
if [ condition ]; then
    # code to execute if the condition is true
fi

# If-else statement
if [ condition ]; then
    # code to execute if the condition is true
else
    # code to execute if the condition is false
fi

# Example
if [ $num -gt 10 ]; then
    echo "Greater than 10"
else
    echo "Less than or equal to 10"
fi

3. Loops

# For loop
for i in {1..5}; do
    echo $i
done

# While loop
counter=0
while [ $counter -lt 5 ]; do
    echo $counter
    ((counter++))
done

# Until loop
counter=0
until [ $counter -ge 5 ]; do
    echo $counter
    ((counter++))
done

4. Functions

# Declare a function
function_name() {
    # code for the function
}

# Call a function
function_name

# Function with parameters
greet() {
    echo "Hello, $1!"
}

# Call function with parameter
greet "John"

5. Input/Output

# Read input
echo "Enter your name:"
read name
echo "Hello, $name!"

# Command substitution
current_date=$(date)
echo "Current date: $current_date"

# Redirect output to a file
echo "Hello, World!" > output.txt

6. File Operations

# Check if a file exists
if [ -e file.txt ]; then
    echo "File exists"
fi

# Check if a directory exists
if [ -d directory ]; then
    echo "Directory exists"
fi

# Copy a file
cp source.txt destination.txt

# Move/Rename a file
mv oldname.txt newname.txt

# Remove/Delete a file
rm file.txt

7. Special Variables

# Positional parameters
echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
# and so on...

# Number of arguments
echo "Number of arguments: $#"

# Last command exit status
echo "Last command exit status: $?"

8. Miscellaneous

# Sleep for n seconds
sleep 5

# Case statement
case $variable in
    pattern1)
        # code for pattern1
        ;;
    pattern2)
        # code for pattern2
        ;;
    *)
        # default code
        ;;
esac

This cheatsheet covers the fundamental aspects of Bash programming. Keep it handy, and it will serve as a quick reference guide to help you write efficient and effective Bash scripts. Happy coding!

Refer to some more documents for in-dept knowledge on Bash Scripting.