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Catalog / Bash Scripting Cheatsheet

Bash Scripting Cheatsheet

A concise reference for Bash scripting, covering essential syntax, commands, and best practices.

Bash Basics

Script Structure

#!/bin/bash - Shebang, specifies the interpreter.
It’s important to include this at the beginning of your bash scripts.

# Comments - Use # for single-line comments.

exit 0 - Exit the script with a success code (0).

Variables

variable="value"

Assign a value to a variable. No spaces around =.

$variable or ${variable}

Access the value of a variable. Use ${} for clarity.

readonly variable

Make a variable read-only.

unset variable

Unset a variable.

export variable

Export a variable to the environment.

Input/Output

echo "message"

Print a message to standard output.

read variable

Read input from standard input into a variable.

cat file

Display the contents of a file.

> file

Redirect output to a file (overwrite).

>> file

Redirect output to a file (append).

Control Flow

Conditional Statements 

if [ condition ]; then
  # commands
elif [ condition ]; then
  # more commands
else
  # default commands
fi

Example:

if [ "$1" == "start" ]; then
  echo "Starting service..."
elif [ "$1" == "stop" ]; then
  echo "Stopping service..."
else
  echo "Invalid command"
fi

Looping

For loop:

for variable in item1 item2 ... itemN; do
  # commands
done

Example:

for i in 1 2 3 4 5; do
  echo "Number: $i"
done

While loop:

while [ condition ]; do
  # commands
done

Example:

count=0
while [ $count -lt 5 ]; do
  echo "Count: $count"
  count=$((count + 1))
done

Until loop:

until [ condition ]; do
  # commands
done

Case Statements 

case variable in
  pattern1 )
    # commands
    ;;
  pattern2 )
    # commands
    ;;
  * )
    # default commands
    ;;
esac

Example:

case "$1" in
  start )
    echo "Starting service..."
    ;;
  stop )
    echo "Stopping service..."
    ;;
  * )
    echo "Invalid command"
    ;;
esac

Functions

Defining Functions 

function function_name() {
  # commands
}

Or:

function_name() {
  # commands
}

Defines a function named function_name.

return value

Returns a value from the function. The value must be between 0 and 255.

Calling Functions

function_name arg1 arg2

Calls the function function_name with arguments arg1 and arg2.

$1, $2, etc.

Access the arguments passed to the function.

$#

Number of arguments passed to the function.

$@

All arguments passed to the function.

Example Function 

function greet() {
  echo "Hello, $1!"
  return 0
}

greet "World"

Command Line Arguments

Accessing Arguments

$0

The name of the script.

$1, $2, etc.

The first, second, etc., command-line argument.

$#

The number of command-line arguments.

$@

All the command-line arguments as a list.

$*

All the command-line arguments as a single string.

Argument Parsing 

while [[ $# -gt 0 ]]; do
  case "$1" in
    -a|--argument1 )
      argument1_value="$2"
      shift 2
      ;;
    -b|--argument2 )
      argument2_value="$2"
      shift 2
      ;;
    * )
      echo "Unknown argument: $1"
      exit 1
      ;;
  esac
done

A common pattern for parsing command-line arguments.
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