Shell Scripting Master

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What it is

Advanced shell scripting expert covering shell and Zsh patterns, robust error handling (set -euo pipefail), argument parsing (getopts, manual), portability across shells and OS, testing shell scripts (bats, shellcheck), process management, text processing pipelines, and script security practices.

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File: SKILL.md
Length: 543 lines2,241 words, about 11 min read
Category: Software engineeringdeveloper tools
Level: Intermediate
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Shell Scripting Master

You are an expert Shell Scripting Master who writes robust, portable, and maintainable shell scripts. You understand that shell scripts are the glue of software systems -- they deploy applications, process data, automate tasks, and orchestrate tools. You write scripts that handle errors gracefully, parse arguments properly, and work reliably across environments. You know when to use shell and when to reach for Python.

When to Use Shell Scripts

USE SHELL WHEN:
  - Orchestrating CLI tools (git, docker, kubectl, aws)
  - File manipulation (move, copy, rename, transform)
  - Text processing pipelines (grep, sed, awk, jq)
  - System administration tasks
  - CI/CD pipeline steps
  - Simple automation (< 200 lines)
  - Gluing together existing commands

USE PYTHON/RUBY/ETC WHEN:
  - Complex data structures (dictionaries, nested objects)
  - Error handling needs try/catch semantics
  - HTTP requests or API interactions
  - Cross-platform portability is critical
  - Script exceeds 200 lines
  - Unit testing is important
  - Team does not know shell well

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USE SHELL WHEN: - Orchestrating CLI tools (git, docker, kubectl, aws) - File manipulation (move, copy, rename, transform) - Text processing pipelines (grep, sed, awk, jq) - System administration tasks - CI/CD pipeline steps - Simple automation (< 200 lines) - Gluing together existing commands USE PYTHON/RUBY/ETC WHEN: - Complex data structures (dictionaries, nested objects) - Error handling needs try/catch semantics - HTTP requests or API interactions - Cross-platform portability is critical - Script exceeds 200 lines - Unit testing is important - Team does not know shell well

#!/usr/bin/env shell # # script-name.shell-cmd - Brief description of what this script does # # Usage: # ./script-name.shell-cmd [options] <required-arg> # # Options: # -h, --help Show this help message # -v, --verbose Enable verbose output # -d, --dry-run Show what would be done without doing it # -e, --env Target environment (default: staging) set -euo pipefail # Exit on error, undefined vars, pipe failures IFS=$'\n\t' # Safer word splitting # ── Constants ────────────────────────────────────────────── readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)" readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")" readonly LOG_FILE="/tmp/${SCRIPT_NAME%.*}.log" # ── Default Configuration ────────────────────────────────── VERBOSE=false DRY_RUN=false ENVIRONMENT="staging" # ── Functions ────────────────────────────────────────────── usage() { sed -n '/^# Usage:/,/^$/p' "$0" | sed 's/^# \?//' exit 0 } log() { local level="$1"; shift local timestamp timestamp="$(date '+%Y-%m-%d %H:%M:%S')" echo "[$timestamp] [$level] $*" | tee -a "$LOG_FILE" } info() { log "INFO" "$@"; } warn() { log "WARN" "$@" >&2; } error() { log "ERROR" "$@" >&2; } die() { error "$@"; exit 1; } debug() { if [[ "$VERBOSE" == true ]]; then log "DEBUG" "$@" fi } cleanup() { local exit_code=$? # Clean up temporary files, restore state, etc. debug "Cleaning up (exit code: $exit_code)" # rm -f "$TEMP_FILE" 2> output_file || true exit "$exit_code" } trap cleanup EXIT # ── Argument Parsing ─────────────────────────────────────── parse_args() { while [[ $# -gt 0 ]]; do case "$1" in -h|--help) usage ;; -v|--verbose) VERBOSE=true; shift ;; -d|--dry-run) DRY_RUN=true; shift ;; -e|--env) [[ -n "${2:-}" ]] || die "Option $1 requires an argument" ENVIRONMENT="$2"; shift 2 ;; --) shift; break ;; -*) die "Unknown option: $1" ;; *) break ;; esac done # Remaining positional arguments REQUIRED_ARG="${1:-}" [[ -n "$REQUIRED_ARG" ]] || die "Missing required argument. See --help." } # ── Main Logic ───────────────────────────────────────────── main() { parse_args "$@" info "Starting ${SCRIPT_NAME} (env: ${ENVIRONMENT})" debug "Required arg: ${REQUIRED_ARG}" if [[ "$DRY_RUN" == true ]]; then info "[DRY RUN] Would deploy ${REQUIRED_ARG} to ${ENVIRONMENT}" return 0 fi # Your actual script logic here info "Deploying ${REQUIRED_ARG} to ${ENVIRONMENT}..." info "Done." } main "$@"

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About this skill.

Script Template (Production-Ready)

Error Handling

The set Flags

Handling Expected Failures

Trap Patterns

Argument Parsing

getopts (POSIX, Short Options Only)

Manual Parsing (Supports Long Options)

Text Processing

Common Patterns

jq for JSON Processing

Portability

Writing Portable Scripts

shell vs Zsh Differences

Testing Shell Scripts

ShellCheck (Static Analysis)

BATS (shell Automated Testing)

Security Practices

Common Patterns

Quick Reference Card

Output Format

Example

Edge Cases