bash

name	bash
description	Full Bash development aid. Use when the user wants to create, edit, run, debug, or test Bash shell scripts. Scaffolds files with proper headers, follows Bash best practices, executes scripts, and assists with debugging.
allowed-tools	Read, Write, Edit, Grep, Glob, Bash
argument-hint	["action or filename"]

Bash Development Skill

Assist with all aspects of Bash script development including creating files, writing code, running scripts, debugging, and testing.

Creating New Files

When creating a new Bash script, always include the file header from CLAUDE.md using the Shell scripts (Bash) template. Every script must begin with:

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

After creating a file, make it executable: chmod +x <script.sh>

Running and Testing

• Run scripts with: bash <script.sh> or ./<script.sh>
• Check syntax without executing: bash -n <script.sh>
• Run with debug tracing: bash -x <script.sh>
• Use shellcheck <script.sh> for static analysis (if available)
• For test frameworks, use bats if available in the project

Code Quality

• Always use set -euo pipefail at the top of scripts:
  • -e: exit on error
  • -u: error on undefined variables
  • -o pipefail: catch errors in piped commands
• Quote all variable expansions: "${variable}" not $variable
• Use [[ ]] for conditionals instead of [ ]
• Use $(command) instead of backticks for command substitution
• Use local for variables inside functions
• Use readonly for constants
• Use snake_case for variable and function names
• Use UPPER_SNAKE_CASE for exported environment variables
• Prefer printf over echo for portable output
• Always handle the case where commands fail gracefully

Script Patterns

Argument parsing:

while [[ $# -gt 0 ]]; do
    case "$1" in
        -h|--help) usage; exit 0 ;;
        -v|--verbose) VERBOSE=true; shift ;;
        *) args+=("$1"); shift ;;
    esac
done

Cleanup on exit:

cleanup() {
    rm -f "${tmp_file:-}"
}
trap cleanup EXIT

Logging:

log() { printf '%s %s\n' "$(date '+%Y-%m-%d %H:%M:%S')" "$*" >&2; }

Debugging

Built-in Bash debugging

• Use set -x to trace execution (or bash -x script.sh)
• Use PS4='+(${BASH_SOURCE}:${LINENO}): ' for detailed trace output
• Use trap 'echo "Error on line $LINENO"' ERR for error location
• Check for common issues: unquoted variables, missing error handling, word splitting

ShellCheck (static analysis)

• Run shellcheck <script.sh> to catch bugs, style issues, and portability problems
• Use shellcheck -s bash to explicitly target Bash
• Use shellcheck -e SC2086 to exclude specific rules
• Use shellcheck -f diff to get machine-applicable fix suggestions
• Add inline directives to suppress warnings: # shellcheck disable=SC2086

bashdb (Bash debugger)

• Interactive debugger for Bash scripts, similar to gdb
• Launch with: bashdb <script.sh>
• Key commands:
  • n (next), s (step into), c (continue)
  • b <line> (set breakpoint), d <line> (delete breakpoint)
  • p <expr> (print expression), x <expr> (examine)
  • l (list source), w (where/backtrace)
  • q (quit)
• Install with: brew install bashdb

bats-core (Bash Automated Testing System)

• TAP-compliant testing framework for Bash
• Install with: brew install bats-core
• Test files use .bats extension
• Run tests with: bats test/ or bats test/script.bats
• Test structure:

  @test "description of test" {
      run my_function arg1 arg2
      [ "$status" -eq 0 ]
      [ "$output" = "expected output" ]
  }
  

• Helper libraries:
  • bats-support -- common assertions and output formatting
  • bats-assert -- advanced assertion functions (assert_success, assert_output, assert_line)
  • bats-file -- file system assertions (assert_file_exists, assert_dir_exists)

Argument Handling

• If $ARGUMENTS is a filename ending in .sh, work with that file
• If $ARGUMENTS is "new ", scaffold a new file with proper headers and make it executable
• If $ARGUMENTS is "run ", execute the script and report output
• If $ARGUMENTS is "check ", run shellcheck and syntax validation
• Otherwise, treat $ARGUMENTS as a general Bash development request