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Shell

Shell scripting best practices and conventions for bash, sh, zsh, and other shells

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Shell Scripting Guidelines

Instructions for writing clean, safe, and maintainable shell scripts for bash, sh, zsh, and other shells.

General Principles

  • Generate code that is clean, simple, and concise
  • Ensure scripts are easily readable and understandable
  • Add comments where helpful for understanding how the script works
  • Generate concise and simple echo outputs to provide execution status
  • Avoid unnecessary echo output and excessive logging
  • Use shellcheck for static analysis when available
  • Assume scripts are for automation and testing rather than production systems unless specified otherwise
  • Prefer safe expansions: double-quote variable references ("$var"), use ${var} for clarity, and avoid eval
  • Use modern Bash features ([[ ]], local, arrays) when portability requirements allow; fall back to POSIX constructs only when needed
  • Choose reliable parsers for structured data instead of ad-hoc text processing

Error Handling & Safety

  • Always enable set -euo pipefail to fail fast on errors, catch unset variables, and surface pipeline failures
  • Validate all required parameters before execution
  • Provide clear error messages with context
  • Use trap to clean up temporary resources or handle unexpected exits when the script terminates
  • Declare immutable values with readonly (or declare -r) to prevent accidental reassignment
  • Use mktemp to create temporary files or directories safely and ensure they are removed in your cleanup handler

Script Structure

  • Start with a clear shebang: #!/bin/bash unless specified otherwise
  • Include a header comment explaining the script's purpose
  • Define default values for all variables at the top
  • Use functions for reusable code blocks
  • Create reusable functions instead of repeating similar blocks of code
  • Keep the main execution flow clean and readable

Working with JSON and YAML

  • Prefer dedicated parsers (jq for JSON, yq for YAML—or jq on JSON converted via yq) over ad-hoc text processing with grep, awk, or shell string splitting
  • When jq/yq are unavailable or not appropriate, choose the next most reliable parser available in your environment, and be explicit about how it should be used safely
  • Validate that required fields exist and handle missing/invalid data paths explicitly (e.g., by checking jq exit status or using // empty)
  • Quote jq/yq filters to prevent shell expansion and prefer --raw-output when you need plain strings
  • Treat parser errors as fatal: combine with set -euo pipefail or test command success before using results
  • Document parser dependencies at the top of the script and fail fast with a helpful message if jq/yq (or alternative tools) are required but not installed
#!/bin/bash

# ============================================================================
# Script Description Here
# ============================================================================

set -euo pipefail

cleanup() {
    # Remove temporary resources or perform other teardown steps as needed
    if [[ -n "${TEMP_DIR:-}" && -d "$TEMP_DIR" ]]; then
        rm -rf "$TEMP_DIR"
    fi
}

trap cleanup EXIT

# Default values
RESOURCE_GROUP=""
REQUIRED_PARAM=""
OPTIONAL_PARAM="default-value"
readonly SCRIPT_NAME="$(basename "$0")"

TEMP_DIR=""

# Functions
usage() {
    echo "Usage: $SCRIPT_NAME [OPTIONS]"
    echo "Options:"
    echo "  -g, --resource-group   Resource group (required)"
    echo "  -h, --help            Show this help"
    exit 0
}

validate_requirements() {
    if [[ -z "$RESOURCE_GROUP" ]]; then
        echo "Error: Resource group is required"
        exit 1
    fi
}

main() {
    validate_requirements

    TEMP_DIR="$(mktemp -d)"
    if [[ ! -d "$TEMP_DIR" ]]; then
        echo "Error: failed to create temporary directory" >&2
        exit 1
    fi
    
    echo "============================================================================"
    echo "Script Execution Started"
    echo "============================================================================"
    
    # Main logic here
    
    echo "============================================================================"
    echo "Script Execution Completed"
    echo "============================================================================"
}

# Parse arguments
while [[ $# -gt 0 ]]; do
    case $1 in
        -g|--resource-group)
            RESOURCE_GROUP="$2"
            shift 2
            ;;
        -h|--help)
            usage
            ;;
        *)
            echo "Unknown option: $1"
            exit 1
            ;;
    esac
done

# Execute main function
main "$@"