Bash

Introduction

This cheat sheet provides a quick reference for some common Bash scripting commands and concepts. Bash is a popular Unix shell used for writing and executing shell scripts.

Basic Script Structure

A typical Bash script has the following structure:

#!/bin/bash
# Comments and explanations
# ...

# Variables
variable_name="value"

# Command execution
command1
command2

# Conditional statements
if [ condition ]; then
  # Commands to execute if condition is true
fi

# Loops
for item in list; do
  # Commands to execute for each item
done

# Functions
function_name() {
  # Commands inside the function
}

Variables

• Declare and assign a value to a variable:

  variable_name="value"

• Access the value of a variable:

  echo $variable_name

• Use double quotes for variables containing spaces:

  greeting="Hello, world!"
  echo "$greeting"

Command Execution

• Run a command:

  command_name

• Capture the output of a command:

  result=$(command_name)

• Redirect output to a file:

  command_name > output.txt

Conditional Statements

• Use if statements for conditional execution:

  if [ condition ]; then
    # Commands to execute if condition is true
  fi

• Example: Check if a file exists:

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

Loops

• Use for loops to iterate over a list:

  for item in item1 item2 item3; do
    # Commands to execute for each item
  done

• Example: Iterate through files in a directory:

  for file in *; do
    echo "Processing $file"
  done

Functions

• Define a function:

  function_name() {
    # Commands inside the function
  }

• Call a function:

  function_name

• Pass arguments to a function:

  function_with_args() {
    arg1=$1
    arg2=$2
    echo "Arg1: $arg1, Arg2: $arg2"
  }
  function_with_args value1 value2

Comments

• Add comments to your script using #:

  # This is a comment

Special Variables

• $0: The name of the script.
• $1, $2, ...: Command-line arguments passed to the script.
• $#: The number of command-line arguments.
• $?: The exit status of the last command.
• $$: The process ID of the script.

Conclusion

This cheat sheet covers some common Bash scripting commands and concepts. Bash scripting provides extensive capabilities; refer to the Bash documentation for more in-depth information and advanced usage.