Bash Master

Expert bash/shell scripting across environments where Bash is available (Linux, macOS, Git Bash on Windows, WSL, containers). This is a Bash-focused skill - it does not provide PowerShell parity; on Windows the target is the Bash interpreter (Git Bash / WSL), not native PowerShell. PROACTIVELY activate for: (1) ANY bash/shell script task, (2) System automation, (3) DevOps/CI/CD scripts, (4) Build/deployment automation, (5) Script review/debugging, (6) Converting commands to scripts. Provides: Google Shell Style Guide compliance, ShellCheck validation, Bash portability across Linux/macOS/WSL/Git Bash/containers, POSIX compliance, security hardening, error handling, performance optimization, testing with BATS, and production-ready patterns. Ensures professional-grade, secure, portable Bash scripts every time.

Bash 5.3 new features and modern patterns (2025). PROACTIVELY activate for: (1) Bash 5.3 specific features (BASH_TRAPSIG, in-shell command substitution, ${|} REPLY syntax), (2) checking bash version compatibility, (3) migrating scripts to take advantage of 5.3 additions, (4) C23 conformance changes in bash 5.3, (5) new shopt and bind options, (6) trap handling improvements, (7) wait -p enhancements, (8) READLINE_ARGUMENT and history expansion changes. Provides: complete 5.3 feature reference, version-detection snippets, compatibility shims for older bash, migration recipes, and POSIX.1-2024 alignment notes.

Security-first bash scripting patterns for 2025 (mandatory validation, zero-trust). PROACTIVELY activate for: (1) reviewing or writing security-sensitive bash scripts, (2) preventing command injection via input validation, (3) safely handling untrusted input (URLs, filenames, env vars), (4) protecting HISTFILE and avoiding secret leakage, (5) safe temporary file creation (mktemp), (6) absolute paths and PATH hardening, (7) avoiding eval and dynamic command construction, (8) signal handling for cleanup, (9) ShellCheck SC2068 / SC2086 compliance. Provides: mandatory-validation patterns, secret-handling rules, mktemp recipes, signal-safe cleanup, and a security review checklist.

ShellCheck validation as a non-negotiable 2025 workflow practice. PROACTIVELY activate for: (1) running ShellCheck on bash scripts, (2) interpreting and fixing ShellCheck warnings (SC2086, SC2068, SC2155, SC2295, SC2327, SC2328, SC2294), (3) integrating ShellCheck into CI (GitHub Actions, Azure DevOps, pre-commit), (4) per-line and per-file disable directives (when justified), (5) shellcheck-rc and project configuration, (6) ShellCheck v0.11.0 new checks, (7) suppressing false positives correctly. Provides: ShellCheck install/CI setup, common warning catalog with fixes, CI workflow templates, and a quality gate pattern that fails builds on regressions.

Advanced bash array patterns including indexed and associative arrays, mapfile/readarray, slicing, and array manipulation (2025). PROACTIVELY activate for: (1) using bash arrays effectively, (2) reading file contents into an array via mapfile/readarray, (3) authoring associative arrays (declare -A), (4) iterating arrays safely under set -u, (5) deleting/inserting array elements, (6) joining and splitting arrays, (7) passing arrays to functions via nameref (declare -n), (8) array slicing and parameter expansion, (9) sorting and deduplicating arrays in pure bash. Provides: indexed and associative array reference, mapfile and readarray recipes, nameref-based pass-by-reference, slicing/expansion patterns, and gotchas for unset variables and word splitting.

Modern DevOps and CI/CD bash automation patterns with containers and cloud (2025). PROACTIVELY activate for: (1) writing CI/CD scripts (GitHub Actions, GitLab CI, Azure DevOps), (2) container-aware shell scripting (detecting containers, Kubernetes pods), (3) cloud provider helpers (AWS CLI, Azure CLI, gcloud), (4) blue-green and canary deployments via bash, (5) writing idempotent rollback scripts, (6) integrating with Docker/Compose from bash, (7) cross-environment variable management, (8) build matrix orchestration. Provides: copy-pasteable CI snippets, container detection helpers, cloud CLI wrappers, deployment orchestration patterns, and idempotent rollback templates.

Process substitution, named pipes (FIFOs), and advanced IPC patterns for efficient bash data streaming (2025). PROACTIVELY activate for: (1) using process substitution with <(cmd) and >(cmd), (2) creating named pipes (mkfifo) for inter-process streaming, (3) avoiding intermediate temp files in pipelines, (4) tee-ing into multiple consumers, (5) feeding diff/comm with command output, (6) building shell-only producers and consumers, (7) reading from a FIFO with timeout, (8) signal-safe FIFO cleanup. Provides: process substitution patterns, mkfifo recipes, multi-consumer tee patterns, and signal-safe cleanup with trap.

Advanced bash string manipulation including parameter expansion, pattern matching, regex, and text processing (2025). PROACTIVELY activate for: (1) parameter expansion (prefix/suffix removal, search/replace, substring), (2) regex matching with [[ =~ ]] and BASH_REMATCH, (3) case modification (uppercase/lowercase), (4) substring extraction without sed/awk, (5) splitting strings into arrays via IFS, (6) escaping for safe interpolation, (7) URL encoding and decoding in pure bash, (8) trimming whitespace, (9) avoiding subshell overhead in tight loops. Provides: parameter-expansion cheat sheet, regex patterns with BASH_REMATCH examples, case-conversion recipes, and IFS-based splitting/joining patterns.

Parallel and concurrent processing patterns in bash including GNU Parallel, xargs -P, job pools, and async patterns (2025). PROACTIVELY activate for: (1) running tasks in parallel from bash, (2) xargs -P for parallel command execution, (3) GNU parallel for complex distribution, (4) background jobs with & and wait, (5) implementing a concurrency cap (job pool of N workers), (6) collecting exit codes from parallel children, (7) preventing race conditions in shared output files, (8) parallel file processing across many cores. Provides: xargs -P recipes, GNU parallel quick reference, job-pool implementations in pure bash, exit-code aggregation patterns, and FIFO-based work queues.

Comprehensive bash script debugging and troubleshooting techniques for 2025. PROACTIVELY activate for: (1) debugging a misbehaving bash script, (2) using set -x, set -e, set -u, set -o pipefail (strict mode), (3) customizing PS4 for richer trace output, (4) trap DEBUG, ERR, and EXIT for diagnostics, (5) bashdb and other interactive debuggers, (6) profiling slow scripts (timing, BASH_REMATCH overhead), (7) reproducing CI-only failures locally, (8) resolving unbound variable or command not found errors, (9) understanding subshell vs current-shell variable scope. Provides: strict-mode template, PS4 patterns, trap recipes for instrumentation, profiling techniques, and a step-by-step debugging playbook.