Sure, here's a comprehensive shell (Bash) scripting standards document, aligned with the principles and structure we established for the HTML standards.

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# Shell (Bash) Scripting Standards Documentation

## Introduction

This document outlines our conventions and best practices for writing **Shell (Bash) scripts**. Adhering to these standards ensures our scripts are **consistent, readable, maintainable, and robust**. By following these guidelines, we'll foster **easier collaboration**, **reduce debugging time**, and **improve script reliability**.

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## Script Structure and Headers

Consistent script structure and informative headers are crucial for immediate understanding and maintainability.

  * **Shebang Line**: Always start with the shebang line specifying the interpreter.
      * **Description**: Ensures the script runs with Bash, regardless of the user's default shell.
      * **Usage**: `#!/bin/bash`
  * **Script Header Comments**: Include a standardized block at the top of each script.
      * **Description**: Provides essential metadata for quick reference.
      * **Usage**:
        ```bash
        #!/bin/bash

        # Script Name:     myscript.sh
        # Description:     This script automates the backup of project files.
        # Author:          Your Name <your.email@example.com>
        # Date:            2025-06-30
        # Version:         1.0.0
        # Usage:           ./myscript.sh [--options] <arguments>
        # Dependencies:    rsync, tar
        # License:         MIT (or your chosen license)
        ```
  * **Error Handling (Immediate Exit)**:
      * **Description**: Always include `set -e` and `set -u`.
          * `set -e`: Exit immediately if a command exits with a non-zero status. This prevents scripts from continuing in an error state.
          * `set -u`: Treat unset variables as an error and exit immediately. This helps catch typos and uninitialized variables.
          * `set -o pipefail`: (Optional but recommended) Causes a pipeline to return the exit status of the last command in the pipe that exited with a non-zero status, rather than just the last command.
      * **Usage**:
        ```bash
        #!/bin/bash
        set -euo pipefail # All three combined
        ```

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## Naming Conventions

Consistent naming makes variables, functions, and files easy to identify and understand.

### 1\. Variables

  * **Lowercase with Underscores (snake\_case)**:
      * **Description**: For general script variables.
      * **Usage**: `file_name`, `user_input`, `temp_directory`
  * **Uppercase with Underscores (SCREAMING\_SNAKE\_CASE)**:
      * **Description**: For **constants** (values that should not change) and **environment variables**.
      * **Usage**: `MAX_RETRIES=5`, `LOG_FILE="/var/log/app.log"`, `PATH`
  * **Positional Parameters**:
      * **Description**: Refer to script arguments using `$1`, `$2`, etc., and use `$@` for all arguments.
      * **Usage**: `echo "First arg: $1"`, `for arg in "$@"; do ... done`

### 2\. Functions

  * **Lowercase with Underscores (snake\_case)**:
      * **Description**: For function names. Verb-noun structure is often helpful.
      * **Usage**: `display_help`, `process_file`, `cleanup_temp_files`

### 3\. Files

  * **Lowercase with Hyphens (kebab-case)**:
      * **Description**: For script filenames. Avoid spaces.
      * **Usage**: `backup-database.sh`, `deploy-app.sh`, `monitor-logs.sh`

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## Formatting and Readability

Clean formatting significantly improves readability and navigability.

### 1\. Indentation

  * **Spaces over Tabs**:
      * **Description**: Use **4 spaces** for indentation. Configure your editor to convert tabs to spaces.
  * **Consistent Indentation**:
      * **Description**: Indent blocks of code within `if`, `for`, `while`, `function`, etc. consistently.

### 2\. Spacing

  * **Operators and Assignments**:
      * **Description**: Use spaces around operators (`=`, `==`, `!=`, `<`, `>`) and assignments.
      * **Usage**: `variable = "value"`, `if [[ $a -eq $b ]]`, `count=$((count + 1))`
  * **Function Calls**:
      * **Description**: No space between function name and parentheses.
      * **Usage**: `my_function arg1 arg2` (not `my_function(arg1, arg2)`)
  * **Command Separators**:
      * **Description**: Use semicolons `;` only for multiple commands on one line, or for simple `if` statements. Prefer new lines.
      * **Usage**: `command1; command2` (less common), `if [ "$1" == "--help" ]; then display_help; exit 0; fi`

### 3\. Comments

  * **Descriptive Comments**:
      * **Description**: Use `#` for single-line comments. Add comments to explain **why** a piece of code exists, not just **what** it does. Complex logic or non-obvious steps should be commented.
      * **Usage**:
        ```bash
        # Validate that the log file exists before proceeding.
        if [[ ! -f "$LOG_FILE" ]]; then
            echo "Error: Log file not found at $LOG_FILE" >&2
            exit 1
        fi
        ```
  * **Block Comments**:
      * **Description**: For larger explanations or section headers.
      * **Usage**:
        ```bash
        #############################################
        # Function: cleanup_old_backups
        # Description: Deletes backups older than N days.
        #############################################
        ```

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## Best Practices and Principles

These principles guide our overall approach to writing effective and maintainable Bash scripts.

### 1\. Modularity and Functions

  * **Description**: Break down complex scripts into smaller, focused functions. Each function should perform a single, well-defined task.
  * **Benefit**: Improves readability, reusability, and makes debugging easier.
  * **Usage**:
    ```bash
    function validate_input() {
        if [[ -z "$1" ]]; then
            echo "Error: Argument is missing." >&2
            exit 1
        fi
    }

    validate_input "$@"
    ```

### 2\. Argument Parsing

  * **Description**: For scripts that accept options or arguments, use `getopts` for simple options or manual parsing for more complex scenarios. Avoid simple positional checks for multiple options.
  * **Benefit**: Provides a user-friendly interface and robust argument handling.
  * **Usage (`getopts` example)**:
    ```bash
    while getopts "hv:d:" opt; do
        case $opt in
            h) display_help; exit 0 ;;
            v) VERBOSE=true ;;
            d) DEST_DIR="$OPTARG" ;;
            \?) echo "Invalid option: -$OPTARG" >&2; exit 1 ;;
        esac
    done
    shift $((OPTIND - 1)) # Shift positional parameters
    ```

### 3\. Error Handling and Logging

  * **Description**: Beyond `set -e` and `set -u`, implement explicit error checks for critical commands. Redirect error messages to `stderr` (`>&2`) and informative messages to `stdout`. Consider logging to a file for long-running scripts.
  * **Benefit**: Makes scripts more robust and easier to diagnose issues.
  * **Usage**:
    ```bash
    # Command that might fail
    cp source_file.txt dest_dir/ || { echo "Error: Failed to copy file." >&2; exit 1; }

    log_message() {
        echo "$(date '+%Y-%m-%d %H:%M:%S') - $1" >> "$LOG_FILE"
    }

    log_message "Script started."
    ```

### 4\. Quoting Variables

  * **Description**: **Always quote variables** when they contain spaces or special characters to prevent word splitting and globbing. This is one of the most common Bash pitfalls.
  * **Benefit**: Prevents unexpected behavior and ensures commands receive arguments as intended.
  * **Usage**:
    ```bash
    # BAD: May cause issues if file has spaces
    # rm $FILE_PATH

    # GOOD: Safely handles spaces
    rm "$FILE_PATH"

    # For arrays
    for item in "${my_array[@]}"; do
        echo "$item"
    done
    ```

### 5\. Using `[[ ... ]]` over `[ ... ]` (where appropriate)

  * **Description**: Prefer the `[[ ... ]]` (Bash's extended test command) for conditional expressions over the older `[ ... ]` (POSIX `test` command).
  * **Benefit**: `[[ ... ]]` offers more features (like regex matching `==~`, logical operators `&&`, `||`), is less prone to word splitting issues, and provides better readability.
  * **Usage**:
    ```bash
    if [[ "$variable" == "expected value" ]]; then ... fi
    if [[ "$string" =~ ^[0-9]+$ ]]; then echo "Is a number"; fi
    if [[ -f "$file" && -r "$file" ]]; then ... fi
    ```

### 6\. Avoid `ls` Parsing

  * **Description**: Do not parse the output of `ls` (e.g., using `grep` or `awk` on `ls` output) for processing filenames. `ls` output is for human readability, not programmatic use, and can be ambiguous with special characters.
  * **Benefit**: Prevents subtle bugs when dealing with filenames containing spaces, newlines, or other special characters.
  * **Instead**: Use globbing or `find -print0 | xargs -0` for safe file processing.
  * **Usage**:
    ```bash
    # BAD: Don't do this!
    # for file in $(ls *.txt); do ... fi

    # GOOD: Use globbing
    for file in *.txt; do
        echo "Processing '$file'"
    done

    # GOOD: For complex find operations
    find . -name "*.log" -print0 | while IFS= read -r -d $'\0' file; do
        echo "Found log: $file"
    done
    ```

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## Conclusion

By diligently applying these **Bash scripting standards**, we ensure our scripts are not only functional but also **highly readable, maintainable, and robust**. This commitment to quality coding practices promotes a more efficient development workflow and strengthens the reliability of our automated tasks.