shell-scripting

# Shell Scripting

Write reliable, maintainable bash scripts. Covers argument parsing, error handling, portability, temp files, parallel execution, process management, and self-documenting scripts.

## When to Use

- Writing scripts that others (or future you) will run
- Automating multi-step workflows
- Parsing command-line arguments with flags and options
- Handling errors and cleanup properly
- Running tasks in parallel
- Making scripts portable across Linux and macOS
- Wrapping complex commands with a simpler interface

## Script Template

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

# Description: What this script does (one line)
# Usage: script.sh [options] <required-arg>

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "$0")"

# Defaults
VERBOSE=false
OUTPUT_DIR="./output"

usage() {
    cat <<EOF
Usage: $SCRIPT_NAME [options] <input-file>

Description:
  Process the input file and generate output.

Options:
  -o, --output DIR    Output directory (default: $OUTPUT_DIR)
  -v, --verbose       Enable verbose output
  -h, --help          Show this help message

Examples:
  $SCRIPT_NAME data.csv
  $SCRIPT_NAME -v -o /tmp/results data.csv
EOF
}

log() { echo "[$(date '+%H:%M:%S')] $*" >&2; }
debug() { $VERBOSE && log "DEBUG: $*" || true; }
die() { log "ERROR: $*"; exit 1; }

# Parse arguments
while [[ $# -gt 0 ]]; do
    case "$1" in
        -o|--output) OUTPUT_DIR="$2"; shift 2 ;;
        -v|--verbose) VERBOSE=true; shift ;;
        -h|--help) usage; exit 0 ;;
        --) shift; break ;;
        -*) die "Unknown option: $1" ;;
        *) break ;;
    esac
done

INPUT_FILE="${1:?$(usage >&2; echo "Error: input file required")}"
[[ -f "$INPUT_FILE" ]] || die "File not found: $INPUT_FILE"

# Main logic
main() {
    debug "Input: $INPUT_FILE"
    debug "Output: $OUTPUT_DIR"
    mkdir -p "$OUTPUT_DIR"

    log "Processing $INPUT_FILE..."
    # ... do work ...
    log "Done. Output in $OUTPUT_DIR"
}

main "$@"
```...