Pattern	Replacement
`eval`	Never — use arrays
Backticks `cmd`	`$(cmd)`
`for x in $(ls)`	`for x in */` or `mapfile`
`echo` for output	`printf '%s\n'`
`function foo()`	`foo(){ ... }`
`$(basename "$f")`	`${f##*/}`
`$(dirname "$f")`	`${f%/*}`
`$(cat file)`	`$(<file)`
`cat f	cmd`
`cat f	grep`

Required Idioms

# Command existence
has(){ command -v "$1" &>/dev/null; }

# Logging hierarchy
log(){ printf '%b\n' "$*"; }
warn(){ printf '%b\n' "${YLW}WARN:${DEF} $*"; }
err(){ printf '%b\n' "${RED}ERROR:${DEF} $*" >&2; }
die(){ err "$*"; exit "${2:-1}"; }
dbg(){ [[ ${DEBUG:-0} -eq 1 ]] && printf '[DBG] %s\n' "$*" || :; }

# Output params via nameref (no subshell)
get_name(){ local -n _out=$1; _out="${2##*/}"; }

# Array loading from file (strip comments + blank lines)
mapfile -t arr < <(grep -Ev '^\s*(#|$)' file.txt)

# Parallel execution
printf '%s\n' "${items[@]}" | xargs -r -P"$(nproc)" -I{} process {}

Trap Pattern

cleanup(){
  set +e
  [[ -n ${LOCK_FD:-} ]] && exec {LOCK_FD}>&- 2>/dev/null || :
  [[ -d ${WORKDIR:-} ]] && rm -rf "$WORKDIR" || :
}
trap 'cleanup' EXIT
trap 'err "failed at line $LINENO"' ERR
trap ':' INT TERM

Color Palette (trans flag)

LBLU=$'\e[38;5;117m'  # Light blue
PNK=$'\e[38;5;218m'   # Pink
BWHT=$'\e[97m'        # Bright white
DEF=$'\e[0m'          # Reset
BLD=$'\e[1m'          # Bold

Performance: Cost Table

❌ Expensive	✅ Cheap
`$(command)` subshell	`${var//pat/rep}`
`tr`	`${var,,}` / `${var^^}`
`basename`	`${f##*/}`
`dirname`	`${f%/*}`
`cat file`	`$(<file)`

Quoting Rules

Always quote variables: "$var", "${arr[@]}"
Exception: intentional word-split/glob, and $* in printf format
Use -- before user-supplied args to commands: rm -- "$file"

Input Validation

validate_path(){
  [[ $1 =~ ^[[:alnum:]/_.-]+$ ]] || die "invalid path: $1"
  [[ ! $1 =~ \.\. ]] || die "path traversal: $1"
}
validate_pkg(){
  [[ $1 =~ ^[a-z0-9@._+-]+$ ]] || die "invalid pkg: $1"
}

bash-idioms

Required Header

Forbidden Patterns