Shell/Bash Standards

#!/bin/bash
set -euo pipefail
# -e: Exit on error
# -u: Error on undefined variables
# -o pipefail: Pipe fails if any command fails

#!/bin/bash
set -euo pipefail
 
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"
 
cleanup() {
    rm -f "$SCRIPT_DIR"/*.tmp 2>/dev/null || true
}
trap cleanup EXIT
 
error_handler() {
    echo "Error on line $1" >&2
    exit 1
}
trap 'error_handler $LINENO' ERR
 
main() {
    echo "Running $SCRIPT_NAME"
}
 
main "$@"

# Always quote variables
echo "$var"                     # Good
echo $var                       # Bad - word splitting
 
# Use [[ ]] for conditionals
if [[ -f "$file" ]]; then       # Good (Bash)
if [ -f "$file" ]; then         # POSIX only
 
# Local variables in functions
get_user_name() {
    local user_id=$1
    local name
    name=$(grep "^${user_id}:" /etc/passwd | cut -d: -f5)
    echo "$name"
}
 
# Parameter expansion
${var:-default}             # Use default if unset
${var:?error message}       # Error if unset
${file%%.*}                 # Remove extension

# Read file line by line
while IFS= read -r line; do
    echo "Line: $line"
done < "input.txt"
 
# Safe temp files
temp_file=$(mktemp)
trap 'rm -f "$temp_file"' EXIT
 
# Process files with spaces
find . -name "*.txt" -print0 | while IFS= read -r -d '' file; do
    echo "Processing: $file"
done

usage() {
    echo "Usage: $0 [-v] [-o output] [-h]"
    exit 1
}
 
verbose=false
output_file=""
 
while getopts "vo:h" opt; do
    case $opt in
        v) verbose=true ;;
        o) output_file="$OPTARG" ;;
        h) usage ;;
        *) usage ;;
    esac
done
shift $((OPTIND - 1))

# Run ShellCheck
shellcheck script.sh
 
# Disable specific warning (sparingly)
# shellcheck disable=SC2086
echo $UNQUOTED_VAR