optimizing-bash-scripts

name	optimizing-bash-scripts
description	Analyzes bash scripts for performance bottlenecks, coding standards, and modern tool replacements. Use when optimizing shell scripts, consolidating scripts, or preparing for production. Triggers include "optimize bash", "shellcheck", "script performance", or "consolidate scripts".
allowed-tools	Bash, Read, Edit, Grep, Glob
user-invocable	true

Bash Script Optimizer

Analyze and optimize bash scripts according to strict standards: performance, modern tooling, consolidation patterns.

Quick Start

Analyze a script:

python3 scripts/analyze.py path/to/script.sh

Optimize workflow:

1. Run analyzer on target script(s)
2. Review issues by priority: critical → performance → optimization → standards
3. Apply fixes systematically
4. Validate with shellcheck
5. Test functionality
6. Measure improvement

Core Standards

Scripts must include:

#!/usr/bin/env bash
set -euo pipefail
shopt -s nullglob globstar
IFS=$'\n\t' LC_ALL=C

Style: 2-space indent, minimal blank lines, short CLI args, quoted variables

Native bash: arrays, [[ ]] tests, parameter expansion, process substitution

Modern tools (prefer → fallback):

• fd/fdfind → find
• rg → grep
• sd → sed
• fzf for interactive
• jaq → jq
• choose → cut/awk
• parallel → xargs -P
• gh → git
• aria2/axel → curl → wget

See references/standards.md for complete specification.

Analysis Categories

Critical: Must fix (security, correctness)

• Parsing ls output
• Unquoted variables
• eval usage
• Wrong shebang

Performance: Significant impact

• Unnecessary cat pipes
• Excessive subshells/forks
• Sequential vs parallel opportunities
• Uncached expensive operations

Optimization: Modern alternatives

• find → fd (3-5x faster)
• grep → rg (10x+ faster)
• sed → sd (cleaner syntax)
• Legacy tool replacement opportunities

Standards: Code quality

• vs [[ ]]
• echo vs printf
• Indentation (2-space)
• function syntax (prefer fn(){})

Consolidation Patterns

When to consolidate multiple scripts:

• Shared validation/setup logic
• Common function libraries
• Similar workflows with parameter variations
• Reduce maintenance burden

Unified entry point pattern:

mode=${1:-}
case $mode in
  action1) shift; action1_fn "$@";;
  action2) shift; action2_fn "$@";;
  *) die "Usage: $0 {action1|action2}";;
esac

Shared library extraction: Extract common functions to lib/common.sh, source in scripts.

Configuration-driven logic: Replace script proliferation with data structures (assoc arrays).

See references/patterns.md for detailed consolidation strategies.

Optimization Workflow

1. Baseline Analysis

Run analyzer on all target scripts. Prioritize by issue count/severity.

2. Quick Wins

• Replace cat pipes: cat f | grep → grep < f
• Convert tests: [ ] → [[ ]]
• Quote variables: $var → "$var"
• Add missing options: set -euo pipefail

3. Tool Modernization

Replace legacy tools where available:

# Check availability
command -v fd &>/dev/null && use_fd=1

# Fallback pattern
if [[ $use_fd ]]; then
  fd -tf '\.sh$'
else
  find . -type f -name '*.sh'
fi

4. Performance Optimization

• Batch operations: Collect items, process in parallel
• Cache results: Avoid repeated expensive calls
• Reduce forks: Use bash builtins vs external commands
• Process substitution: < <(cmd) vs cmd |

5. Consolidation

If analyzing multiple related scripts:

• Extract shared functions
• Unify entry points
• Create configuration-driven logic
• Document migration

6. Validation

• Shellcheck clean
• Bash execution test
• Functionality verification
• Performance measurement (time, profiling)

Common Refactorings

Remove unnecessary subshells:

# Before: count=$(cat file | wc -l)
# After: count=$(wc -l < file)
# Better: mapfile -t lines < file; count=${#lines[@]}

Parallel processing:

# Before: for f in *.txt; do process "$f"; done
# After: printf '%s\n' *.txt | rust-parallel -j"$(nproc)" process

Parameter expansion over sed:

# Before: echo "$file" | sed 's/\.txt$//'
# After: printf '%s\n' "${file%.txt}"

Batch I/O:

# Before: while read line; do echo "prefix $line" >> out; done < in
# After:
output=()
while read -r line; do output+=("prefix $line"); done < in
printf '%s\n' "${output[@]}" > out

Token Efficiency

Compress documentation:

• Cause → effect: ⇒ notation
• Lists: ≤7 items
• Minimize whitespace: Prefer compact over verbose

Example:

# Verbose (44 tokens)
# This function checks if the required tools are available
# in the system PATH and exits with an error if any are missing.
# It takes a list of tool names as arguments.

# Compact (16 tokens)
# Verify required tools exist ⇒ exit if missing

Tips

• Analyze before bulk edits
• Test incrementally, not all at once
• Keep shellcheck clean at each step
• Measure performance impact when optimizing
• Document consolidation rationale
• Maintain fallback chains for tools

Resources

• scripts/analyze.py - Automated script analyzer
• references/standards.md - Complete coding standards
• references/patterns.md - Optimization patterns and consolidation strategies