How to write better scripts

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Writing High-Quality Bash Scripts

Here's what separates solid bash scripts from fragile ones:

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Always Start with a Strict Header

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

• set -e — exit immediately on error

• set -u — treat unset variables as errors

• set -o pipefail — catch errors in pipelines (e.g., cmd1 | cmd2)

• IFS=$'\n\t' — safer word splitting (avoids space-splitting bugs)

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Quote Everything

Unquoted variables are a common source of bugs:

# Bad
cp $file $destination

# Good
cp "$file" "$destination"

This matters when filenames contain spaces or special characters.

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Use Functions

Break logic into named functions. It makes scripts readable and testable:

log() {
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" >&2
}

cleanup() {
  rm -f "$tmpfile"
  log "Cleaned up."
}

trap cleanup EXIT  # Always runs on exit

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Handle Errors Explicitly

Don't rely solely on set -e. Check critical commands:

if ! cp "$src" "$dst"; then
  echo "Error: failed to copy $src to $dst" >&2
  exit 1
fi

Print errors to stderr (>&2), not stdout.

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Use trap for Cleanup

tmpfile=$(mktemp)
trap 'rm -f "$tmpfile"' EXIT

This ensures temp files are removed even if the script crashes.

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Validate Inputs Early

if [[ $# -lt 2 ]]; then
  echo "Usage: $(basename "$0") <source> <destination>" >&2
  exit 1
fi

src="$1"
dst="$2"

[[ -f "$src" ]] || { echo "Error: $src not found" >&2; exit 1; }

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Use [[ ]] Instead of [ ]

[[ ]] is the modern bash conditional — it handles edge cases better:

# Safer string comparison
if [[ "$name" == "admin" ]]; then ...

# Safe file existence check (no issue with empty vars)
if [[ -f "$file" ]]; then ...

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Prefer $(...) Over Backticks

# Old style (hard to nest, hard to read)
result=`date`

# Modern style
result=$(date)

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Name Variables Clearly

# Bad
a="$1"
b="$2"

# Good
input_file="$1"
output_dir="$2"

Use UPPER_CASE for exported/global variables and lower_case for locals.

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Add a Usage/Help Function

usage() {
  cat <<EOF
Usage: $(basename "$0") [OPTIONS] <input>

Options:
  -h, --help     Show this help message
  -v, --verbose  Enable verbose output
EOF
}

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Use local in Functions

process_file() {
  local file="$1"
  local count=0
  # ...
}

Without local, variables leak into global scope.

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Lint Your Scripts

Use ShellCheck — it catches an enormous range of bugs:

shellcheck myscript.sh

It's available in most package managers (apt install shellcheck, brew install shellcheck) and has VS Code/Vim/Emacs plugins.

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Putting It Together — A Template

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

# ── Constants ──────────────────────────────────────────
SCRIPT_NAME="$(basename "$0")"

# ── Helpers ────────────────────────────────────────────
log()   { echo "[$SCRIPT_NAME] $*" >&2; }
die()   { echo "[$SCRIPT_NAME] ERROR: $*" >&2; exit 1; }
usage() {
  echo "Usage: $SCRIPT_NAME <input_file> <output_dir>"
  exit 0
}

# ── Cleanup ────────────────────────────────────────────
tmpfile=$(mktemp)
trap 'rm -f "$tmpfile"' EXIT

# ── Argument Parsing ───────────────────────────────────
[[ $# -lt 2 ]] && usage

input_file="$1"
output_dir="$2"

[[ -f "$input_file" ]] || die "Input file not found: $input_file"
[[ -d "$output_dir" ]] || die "Output directory not found: $output_dir"

# ── Main Logic ─────────────────────────────────────────
main() {
  log "Processing $input_file..."
  # your logic here
  log "Done."
}

main "$@"

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The single biggest improvement you can make is running ShellCheck on everything you write. It'll teach you more than almost anything else.

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