Bash Coding Standard

Metrolla has adopted the Google Coding Standard for Bash scripts.

Google's style guide for Bash scripting emphasizes writing clean, maintainable, and portable shell scripts. Below is a summary of the key points from the guide:

Google Bash Style Guide

1. General Principles

• Clarity: Write clear and understandable scripts.
• Consistency: Follow established coding conventions and structures.
• Portability: Ensure scripts are portable across different environments.

2. Shebang

• Use #!/bin/bash for Bash scripts.

  #!/bin/bash

3. File Extension

• Use .sh as the file extension for shell scripts.

4. Comments

• Use comments to explain the purpose of the script, significant sections, and complex logic.

  # This script calculates the sum of two numbers.

5. Formatting

• Indentation: Use 2 spaces for indentation. Avoid tabs.

  if [ "$condition" ]; then
    echo "Condition met"
  fi

• Line Length: Limit lines to 80 characters.
• Line Breaks: Use line breaks to separate logical sections of the script.

6. Variables

• Naming: Use lower_snake_case for variable names.
• Initialization: Always initialize variables.

  my_variable="value"

• Readonly Variables: Use readonly for constants.

  readonly MY_CONSTANT="constant_value"

7. Quoting

• Double Quotes: Use double quotes to prevent word splitting and globbing.

  my_var="some value"
  echo "$my_var"

• Single Quotes: Use single quotes for literals that don't need variable interpolation.

  echo 'Literal string'

8. Tests

• Use [ (also known as test) for testing conditions, with spaces around the brackets.

  if [ "$var" -eq 1 ]; then
    echo "Variable equals 1"
  fi

9. Functions

• Define functions using function keyword.
• Use lower_snake_case for function names.
• Place all function definitions at the start of the script.

  function my_function {
    echo "Function body"
  }

10. Error Handling

• Use set -e to exit on error.
• Use set -u to treat unset variables as an error.
• Use trap to clean up temporary files and handle signals.

  set -e
  set -u
  
  trap 'rm -f /tmp/my_temp_file' EXIT
  
  function cleanup {
    rm -f /tmp/my_temp_file
  }
  
  trap cleanup EXIT

11. Input and Output

• Use read for input.
• Use echo for output.

  read -p "Enter your name: " name
  echo "Hello, $name"

12. Scripts Structure

• Structure scripts with the following sections:
  1. Shebang
  2. Comments and License Information
  3. Imports and Global Variables
  4. Functions
  5. Main Script Execution

13. Portability

• Avoid using Bash-specific features if possible.
• Prefer POSIX-compliant code for better portability.

Example Script

Here is an example that illustrates some of these standards:

#!/bin/bash

# This script demonstrates a simple greeting.

# Constants
readonly SCRIPT_NAME=$(basename "$0")

# Function to print usage
function print_usage {
  echo "Usage: $SCRIPT_NAME <name>"
}

# Main function
function main {
  if [ "$#" -ne 1 ]; then
    print_usage
    exit 1
  fi

  local name="$1"
  echo "Hello, $name"
}

# Script entry point
main "$@"

For the most detailed and up-to-date information, refer to the full Google Shell Style Guide.