Bash Script Generator

Bash Script Generator

Overview

This skill provides a comprehensive workflow for generating production-ready bash scripts with best practices built-in. Generate scripts for system administration, text processing, API clients, automation workflows, and more with robust error handling, logging, argument parsing, and validation.

When to Use This Skill

Invoke this skill when:

• Creating new bash scripts from scratch
• Implementing shell automation or system administration tasks
• Building command-line tools and utilities
• Creating text processing workflows (log analysis, data transformation, etc.)
• Converting manual command sequences into reusable scripts
• Implementing deployment or build automation scripts
• Creating cron jobs or scheduled tasks
• The user asks to "create", "generate", "build", or "write" a bash script
• Implementing scripts that use grep, awk, sed, or other text processing tools

Mandatory Steps (DO NOT SKIP)

The following steps are REQUIRED for every script generation. Skipping these steps will result in scripts that don't meet user needs or fail validation.

MANDATORY: Pre-Generation Requirements

BEFORE generating any script, you MUST complete these steps:

1. Clarify Requirements with User (REQUIRED)

Use AskUserQuestion tool if ANY of the following are unclear or unspecified:

DO NOT skip this step. Assumptions lead to scripts that don't meet user needs.

2. Explain Your Approach (REQUIRED)

Before writing code, explain to the user:

1. Script Architecture: What components and functions you'll create
2. Tool Selection: Why you're choosing grep/awk/sed/etc. for specific tasks
   • Reference: docs/text-processing-guide.md for tool selection rationale
3. Key Design Decisions: Any tradeoffs or assumptions you're making
4. Customization Points: What the user might want to modify

Example pre-generation explanation:

I'll create a log analyzer with these components:

**Architecture:**
- Main function with argument parsing (getopts pattern)
- 4 analysis functions: analyze_ips(), analyze_status_codes(), etc.
- Logging functions for INFO/DEBUG/ERROR output
- Cleanup trap for signal handling

**Tool Selection:**
- awk for status code analysis (single-pass counting, as recommended in
  docs/text-processing-guide.md)
- grep for date filtering (simple pattern matching)
- sort | uniq -c for frequency counting

**Customization Points:**
- LOG_FORMAT variable for different nginx configurations
- TOP_N constant for number of results to show

Shall I proceed with this design?

3. Consider Using the Template (RECOMMENDED)

When to use the template:

• Use template for quick starts on standard scripts with typical structure (CLI tools, automation scripts)
• Manual generation is better for highly customized scripts with unique requirements or non-standard architectures

For standard scripts, invoke the template generator:

bash scripts/generate_script_template.sh standard output-script.sh

This ensures consistent structure with all required components pre-configured. The template includes:

• Proper shebang and strict mode
• Logging functions (debug, info, warn, error)
• Error handling (die, check_command, validate_file)
• Argument parsing boilerplate
• Cleanup trap handlers

Then customize the generated template for your specific use case.

Script Generation Workflow

Follow this workflow when generating bash scripts. Adapt based on user needs:

Stage 1: Understand Requirements

Gather information about what the script needs to do:

1. Script purpose:

   • What problem does it solve?
   • What tasks does it automate?
   • Who will use it (developers, ops, cron, CI/CD)?

2. Functionality requirements:

   • Input sources (files, stdin, arguments, APIs)
   • Processing steps (text manipulation, system operations, etc.)
   • Output destinations (stdout, files, logs, APIs)
   • Expected data formats

3. Shell type:

   • Bash-specific (modern systems, can use arrays, associative arrays, etc.)
   • POSIX sh (maximum portability, limited features)
   • Default to bash unless portability is explicitly required

4. Argument parsing:

   • Command-line options needed
   • Required vs optional arguments
   • Help/usage text requirements

5. Error handling requirements:

   • How should errors be handled? (fail fast, retry, graceful degradation)
   • Logging verbosity levels needed?
   • Exit codes required?

6. Performance considerations:

   • Large file processing requirements
   • Parallel processing needs
   • Resource constraints

7. Security requirements:

   • Input validation needs
   • Credential handling
   • Privilege requirements

Use AskUserQuestion if information is missing or unclear.

Stage 2: Architecture Planning

Plan the script structure based on requirements:

1. Determine script components:

   • Functions needed
   • Configuration management approach
   • Logging strategy
   • Error handling approach

2. Select appropriate tools:

   • grep for pattern matching and filtering
   • awk for structured text processing (CSV, logs, columnar data)
   • sed for stream editing and substitution
   • find for file system operations
   • curl/wget for HTTP operations
   • Built-in bash features when possible

3. Plan error handling:

   • Use set -euo pipefail for strict mode (recommended)
   • Define error handling functions
   • Plan cleanup procedures (trap for EXIT, ERR signals)

4. Plan logging:

   • Log levels needed (DEBUG, INFO, WARN, ERROR)
   • Output destinations (stderr for logs, stdout for data)
   • Log formatting

Stage 3: Generate Script Structure

Create the basic script structure:

1. Shebang and header:

#!/usr/bin/env bash
#
# Script Name: script-name.sh
# Description: Brief description of what the script does
# Author: Your Name
# Created: YYYY-MM-DD
#

2. Strict mode (recommended for all scripts):

set -euo pipefail
IFS=$'\n\t'

Explanation:

• set -e: Exit on error
• set -u: Exit on undefined variable
• set -o pipefail: Exit if any command in pipeline fails
• IFS: Set safe Internal Field Separator

3. Script-level variables and constants:

# Script directory and name
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"

# Other constants
readonly DEFAULT_CONFIG_FILE="${SCRIPT_DIR}/config.conf"
readonly LOG_FILE="/var/log/myscript.log"

4. Signal handlers for cleanup:

# Cleanup function
cleanup() {
    local exit_code=$?
    # Add cleanup logic here
    # Remove temp files, release locks, etc.
    exit "${exit_code}"
}

# Set trap for cleanup
trap cleanup EXIT ERR INT TERM

Stage 4: Generate Core Functions

Generate essential functions based on requirements:

Logging Functions

# Logging functions
log_debug() {
    if [[ "${LOG_LEVEL:-INFO}" == "DEBUG" ]]; then
        echo "[DEBUG] $(date '+%Y-%m-%d %H:%M:%S') - $*" >&2
    fi
}

log_info() {
    echo "[INFO] $(date '+%Y-%m-%d %H:%M:%S') - $*" >&2
}

log_warn() {
    echo "[WARN] $(date '+%Y-%m-%d %H:%M:%S') - $*" >&2
}

log_error() {
    echo "[ERROR] $(date '+%Y-%m-%d %H:%M:%S') - $*" >&2
}

log_fatal() {
    echo "[FATAL] $(date '+%Y-%m-%d %H:%M:%S') - $*" >&2
    exit 1
}

Error Handling Functions

# Error handling
die() {
    log_error "$@"
    exit 1
}

# Check if command exists
check_command() {
    local cmd="$1"
    if ! command -v "${cmd}" &> /dev/null; then
        die "Required command '${cmd}' not found. Please install it and try again."
    fi
}

# Validate file exists and is readable
validate_file() {
    local file="$1"
    [[ -f "${file}" ]] || die "File not found: ${file}"
    [[ -r "${file}" ]] || die "File not readable: ${file}"
}

Argument Parsing Function

Using getopts for simple options:

# Parse command-line arguments
parse_args() {
    while getopts ":hvf:o:d" opt; do
        case ${opt} in
            h )
                usage
                exit 0
                ;;
            v )
                VERBOSE=true
                ;;
            f )
                INPUT_FILE="${OPTARG}"
                ;;
            o )
                OUTPUT_FILE="${OPTARG}"
                ;;
            d )
                LOG_LEVEL="DEBUG"
                ;;
            \? )
                echo "Invalid option: -${OPTARG}" >&2
                usage
                exit 1
                ;;
            : )
                echo "Option -${OPTARG} requires an argument" >&2
                usage
                exit 1
                ;;
        esac
    done
    shift $((OPTIND -1))
}

Usage/Help Function

# Display usage information
usage() {
    cat << EOF
Usage: ${SCRIPT_NAME} [OPTIONS] [ARGUMENTS]

Description:
    Brief description of what the script does

Options:
    -h          Show this help message and exit
    -v          Enable verbose output
    -f FILE     Input file path
    -o FILE     Output file path
    -d          Enable debug logging

Examples:
    ${SCRIPT_NAME} -f input.txt -o output.txt
    ${SCRIPT_NAME} -v -f data.log

EOF
}

Stage 5: Generate Business Logic

Implement the core functionality based on requirements:

1. For text processing tasks, use appropriate tools:

   • grep: Pattern matching, line filtering
   • awk: Field extraction, calculations, formatted output
   • sed: Stream editing, substitutions, deletions

2. For system administration, include:

   • Validation of prerequisites
   • Backup procedures
   • Rollback capabilities
   • Progress indicators

3. For API clients, include:

   • HTTP error handling
   • Retry logic
   • Authentication handling
   • Response parsing

Stage 6: Generate Main Function

Create the main execution flow:

# Main function
main() {
    # Parse arguments
    parse_args "$@"

    # Validate prerequisites
    check_command "grep"
    check_command "awk"

    # Validate inputs
    [[ -n "${INPUT_FILE:-}" ]] || die "Input file not specified. Use -f option."
    validate_file "${INPUT_FILE}"

    log_info "Starting processing..."

    # Main logic here
    # ...

    log_info "Processing completed successfully"
}

# Execute main function
main "$@"

Stage 7: Add Documentation and Comments

Add comprehensive comments:

1. Function documentation:

#######################################
# Brief description of what function does
# Globals:
#   VARIABLE_NAME
# Arguments:
#   $1 - Description of first argument
#   $2 - Description of second argument
# Outputs:
#   Writes results to stdout
# Returns:
#   0 if successful, non-zero on error
#######################################
function_name() {
    # Implementation
}

2. Inline comments for complex logic
3. Usage examples in the header or usage function

Stage 8: Validate Generated Script

ALWAYS validate the generated script using the devops-skills:bash-script-validator skill:

Steps:
1. Generate the bash script
2. Invoke devops-skills:bash-script-validator skill with the script file
3. Review validation results
4. Fix any issues identified (syntax, security, best practices, portability)
5. Re-validate until all checks pass
6. Provide summary of generated script and validation status

Validation checklist:

• Syntax is correct (bash -n passes)
• ShellCheck warnings addressed
• Security issues resolved (no command injection, eval with variables, etc.)
• Variables properly quoted
• Error handling implemented
• Functions follow single responsibility principle
• Script follows best practices from documentation

If validation fails, fix issues and re-validate until all checks pass.

Text Processing Tool Selection Guide

Choose the right tool for the job:

Use grep when:

• Searching for patterns in files
• Filtering lines that match/don't match patterns
• Counting matches
• Simple line extraction

Examples:

# Find error lines in log file
grep "ERROR" application.log

# Find lines NOT containing pattern
grep -v "DEBUG" application.log

# Case-insensitive search with line numbers
grep -in "warning" *.log

# Extended regex pattern
grep -E "(error|fail|critical)" app.log

Use awk when:

• Processing structured data (CSV, TSV, logs with fields)
• Performing calculations on data
• Extracting specific fields
• Generating formatted reports
• Complex conditional logic

Examples:

# Extract specific fields (e.g., 2nd and 4th columns)
awk '{print $2, $4}' data.txt

# Sum values in a column
awk '{sum += $3} END {print sum}' numbers.txt

# Process CSV with custom delimiter
awk -F',' '{print $1, $3}' data.csv

# Conditional processing
awk '$3 > 100 {print $1, $3}' data.txt

# Formatted output
awk '{printf "Name: %-20s Age: %d\n", $1, $2}' people.txt

Use sed when:

• Performing substitutions
• Deleting lines matching patterns
• In-place file editing
• Stream editing
• Simple transformations

Examples:

# Simple substitution (first occurrence)
sed 's/old/new/' file.txt

# Global substitution (all occurrences)
sed 's/old/new/g' file.txt

# In-place editing
sed -i 's/old/new/g' file.txt

# Delete lines matching pattern
sed '/pattern/d' file.txt

# Replace only on lines matching pattern
sed '/ERROR/s/old/new/g' log.txt

# Multiple commands
sed -e 's/foo/bar/g' -e 's/baz/qux/g' file.txt

Combining tools in pipelines:

# grep to filter, awk to extract
grep "ERROR" app.log | awk '{print $1, $5}'

# sed to clean, awk to process
sed 's/[^[:print:]]//g' data.txt | awk '{sum += $2} END {print sum}'

# Multiple stages
cat access.log \
    | grep "GET" \
    | sed 's/.*HTTP\/[0-9.]*" //' \
    | awk '$1 >= 200 && $1 < 300 {count++} END {print count}'

Best Practices for Generated Scripts

Security

1. Always quote variables:

# Good
rm "${file}"
grep "${pattern}" "${input_file}"

# Bad - prone to word splitting and globbing
rm $file
grep $pattern $input_file

2. Validate all inputs:

# Validate file paths
[[ "${input_file}" =~ ^[a-zA-Z0-9/_.-]+$ ]] || die "Invalid file path"

# Validate numeric inputs
[[ "${count}" =~ ^[0-9]+$ ]] || die "Count must be numeric"

3. Avoid eval with user input:

# Never do this
eval "${user_input}"

# Instead, use case statements or validated inputs
case "${command}" in
    start) do_start ;;
    stop) do_stop ;;
    *) die "Invalid command" ;;
esac

4. Use $() instead of backticks:

# Good - more readable, can nest
result=$(command)
outer=$(inner $(another_command))

# Bad - hard to read, can't nest
result=`command`

Performance

1. Use built-ins when possible:

# Good - uses bash built-in
if [[ -f "${file}" ]]; then

# Slower - spawns external process
if [ -f "${file}" ]; then

2. Avoid useless use of cat (UUOC):

# Good
grep "pattern" file.txt
awk '{print $1}' file.txt

# Bad - unnecessary cat
cat file.txt | grep "pattern"
cat file.txt | awk '{print $1}'

3. Process in a single pass when possible:

# Good - single awk call
awk '/ERROR/ {errors++} /WARN/ {warns++} END {print errors, warns}' log.txt

# Less efficient - multiple greps
errors=$(grep -c "ERROR" log.txt)
warns=$(grep -c "WARN" log.txt)

Maintainability

1. Use functions for reusable code
2. Keep functions focused (single responsibility)
3. Use meaningful variable names
4. Add comments for complex logic
5. Group related functionality
6. Use readonly for constants

Portability (when targeting POSIX sh)

1. Avoid bash-specific features:

# Bash-specific (arrays)
arr=(one two three)

# POSIX alternative
set -- one two three

# Bash-specific ([[ ]])
if [[ -f "${file}" ]]; then

# POSIX alternative
if [ -f "${file}" ]; then

2. Test with sh:

sh -n script.sh  # Syntax check

Common Script Patterns

Pattern 1: Simple Command-Line Tool

#!/usr/bin/env bash
set -euo pipefail

usage() {
    cat << EOF
Usage: ${0##*/} [OPTIONS] FILE

Process FILE and output results.

Options:
    -h        Show this help
    -v        Verbose output
    -o FILE   Output file (default: stdout)
EOF
}

main() {
    local verbose=false
    local output_file=""
    local input_file=""

    while getopts ":hvo:" opt; do
        case ${opt} in
            h) usage; exit 0 ;;
            v) verbose=true ;;
            o) output_file="${OPTARG}" ;;
            *) echo "Invalid option: -${OPTARG}" >&2; usage; exit 1 ;;
        esac
    done
    shift $((OPTIND - 1))

    input_file="${1:-}"
    [[ -n "${input_file}" ]] || { echo "Error: FILE required" >&2; usage; exit 1; }
    [[ -f "${input_file}" ]] || { echo "Error: File not found: ${input_file}" >&2; exit 1; }

    # Process file
    if [[ -n "${output_file}" ]]; then
        process_file "${input_file}" > "${output_file}"
    else
        process_file "${input_file}"
    fi
}

process_file() {
    local file="$1"
    # Processing logic here
    cat "${file}"
}

main "$@"

Pattern 2: Text Processing Script

#!/usr/bin/env bash
set -euo pipefail

# Process log file: extract errors, count by type
process_log() {
    local log_file="$1"

    echo "Error Summary:"
    echo "=============="

    # Extract errors and count by type
    grep "ERROR" "${log_file}" \
        | sed 's/.*ERROR: //' \
        | sed 's/ -.*//' \
        | sort \
        | uniq -c \
        | sort -rn \
        | awk '{printf "  %-30s %d\n", $2, $1}'

    echo ""
    echo "Total errors: $(grep -c "ERROR" "${log_file}")"
}

main() {
    [[ $# -eq 1 ]] || { echo "Usage: $0 LOG_FILE" >&2; exit 1; }
    [[ -f "$1" ]] || { echo "Error: File not found: $1" >&2; exit 1; }

    process_log "$1"
}

main "$@"

Pattern 3: Batch Processing with Parallel Execution

#!/usr/bin/env bash
set -euo pipefail

# Process a single file
process_file() {
    local file="$1"
    local output="${file}.processed"

    # Processing logic
    sed 's/old/new/g' "${file}" > "${output}"
    echo "Processed: ${file} -> ${output}"
}

# Export function for parallel execution
export -f process_file

main() {
    local input_dir="${1:-.}"
    local max_jobs="${2:-4}"

    # Find all files and process in parallel
    find "${input_dir}" -type f -name "*.txt" -print0 \
        | xargs -0 -P "${max_jobs}" -I {} bash -c 'process_file "$@"' _ {}
}

main "$@"

Helper Scripts

The scripts/ directory contains automation tools to assist with generation:

generate_script_template.sh

Generates a bash script from the standard template with proper structure, error handling, and logging.

Usage:

bash scripts/generate_script_template.sh standard [SCRIPT_NAME]

Example:
  bash scripts/generate_script_template.sh standard myscript.sh

The script will copy the standard template and make it executable. You can then customize it for your specific needs.

Documentation Resources

Core Bash Scripting

docs/bash-scripting-guide.md

• Comprehensive bash scripting guide
• Bash vs POSIX sh differences
• Strict mode and error handling strategies
• Functions, scope, and variable handling
• Arrays and associative arrays
• Parameter expansion techniques
• Process substitution and command substitution
• Best practices and modern patterns

docs/script-patterns.md

• Common bash script patterns and templates
• Argument parsing patterns (getopts, manual)
• Configuration file handling
• Logging frameworks and approaches
• Parallel processing patterns
• Lock file management
• Signal handling and cleanup
• Retry logic and backoff strategies

docs/generation-best-practices.md

• Guidelines for generating quality scripts
• Code organization principles
• Naming conventions
• Documentation standards
• Testing approaches for bash scripts
• Portability considerations
• Security best practices
• Performance optimization techniques

Text Processing Tools

docs/text-processing-guide.md

• When to use grep vs awk vs sed
• Combining tools effectively in pipelines
• Performance optimization for large files
• Common text processing patterns
• Real-world examples and use cases

Tool-Specific References

Note: The following references are available in the devops-skills:bash-script-validator skill and are referenced by this skill:

• bash-reference.md - Bash features and syntax
• grep-reference.md - grep patterns and usage
• awk-reference.md - AWK text processing
• sed-reference.md - sed stream editing
• regex-reference.md - Regular expressions (BRE vs ERE)

Example Scripts

Located in examples/ directory:

log-analyzer.sh

Demonstrates grep, awk, and sed usage for log file analysis. Shows pattern matching, field extraction, and statistical analysis. This example illustrates:

• Using grep to filter log entries
• Using awk for field extraction and formatting
• Using sed for text transformations
• Generating summary reports with proper error handling

Template

Located in assets/templates/ directory:

standard-template.sh

Production-ready template with comprehensive features:

• Proper shebang (#!/usr/bin/env bash) and strict mode
• Logging functions (debug, info, warn, error)
• Error handling (die, check_command, validate_file)
• Argument parsing with getopts
• Cleanup trap handlers
• Usage documentation

Use this template as a starting point and customize based on your specific requirements.

Integration with devops-skills:bash-script-validator

After generating any bash script, automatically invoke the devops-skills:bash-script-validator skill to ensure quality:

Steps:
1. Generate the bash script following the workflow above
2. Invoke devops-skills:bash-script-validator skill with the script file
3. Review validation results (syntax, ShellCheck, security, performance)
4. Fix any issues identified
5. Re-validate until all checks pass
6. Provide summary of generated script and validation status

This ensures all generated scripts:

• Have correct syntax
• Follow bash best practices
• Avoid common security issues
• Are optimized for performance
• Include proper error handling
• Are well-documented

Communication Guidelines (MANDATORY)

These are NOT optional. Follow these guidelines for every script generation:

Before Generation (see "MANDATORY: Pre-Generation Requirements" above)

1. ✅ Ask clarifying questions using AskUserQuestion
2. ✅ Explain your approach and get user confirmation
3. ✅ Consider using the standard template

During Generation (REQUIRED)

You MUST explicitly cite documentation when using patterns or making tool selections. This helps users understand the rationale and learn best practices.

1. In the approach explanation, cite documentation for:

   • Tool selection rationale: "Using awk for field extraction (recommended in docs/text-processing-guide.md for structured data)"
   • Pattern choices: "Using getopts pattern from docs/script-patterns.md"
   • Best practices: "Following strict mode guidelines from docs/bash-scripting-guide.md"

2. In generated code comments, reference documentation:

   # Using single-pass awk processing (per docs/text-processing-guide.md)
   awk '{ip[$1]++} END {for (i in ip) print ip[i], i}' "${log_file}"
   

3. Minimum citation requirement: At least 2 documentation references must appear in:

   • The approach explanation (before code generation)
   • The Post-Generation Summary

After Generation (REQUIRED)

Provide a Post-Generation Summary that includes:

## Generated Script Summary

**File:** path/to/script.sh

**Architecture:**
- [List main functions and their purposes]

**Tool Selection:**
- grep: [why used]
- awk: [why used]
- sed: [why used, or "not needed"]

**Key Features:**
- [Feature 1]
- [Feature 2]

**Customization Points:**
- `VARIABLE_NAME`: [what to change]
- `function_name()`: [when to modify]

**Usage Examples:**
```bash
./script.sh --help
./script.sh -v input.log
./script.sh -o report.txt input.log

Validation Status: ✅ Passed ShellCheck / ❌ Issues found (fixing...)

Documentation References:

• docs/text-processing-guide.md (tool selection)
• docs/script-patterns.md (argument parsing)

This summary ensures users understand what was generated and how to use it.

## Resources

### Official Documentation
- [GNU Bash Manual](https://www.gnu.org/software/bash/manual/bash.html)
- [GNU grep Manual](https://www.gnu.org/software/grep/manual/grep.html)
- [GNU awk Manual](https://www.gnu.org/software/gawk/manual/gawk.html)
- [GNU sed Manual](https://www.gnu.org/software/sed/manual/sed.html)
- [POSIX Shell Specification](https://pubs.opengroup.org/onlinepubs/9699919799/)
- [ShellCheck](https://www.shellcheck.net/)

### Best Practices Guides
- [Google Shell Style Guide](https://google.github.io/styleguide/shellguide.html)
- [Bash Best Practices](https://bertvv.github.io/cheat-sheets/Bash.html)
- [Minimal Safe Bash Script Template](https://betterdev.blog/minimal-safe-bash-script-template/)

### Internal References
All documentation is included in the `docs/` directory for offline reference and context loading.

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**Note**: This skill automatically validates generated scripts using the devops-skills:bash-script-validator skill, providing Claude with comprehensive feedback to ensure high-quality, production-ready bash scripts.