Zsh Mastery

Write idiomatic zsh. If the user wanted bash, they'd ask for bash. If they wanted portable sh, they'd ask for sh. When they say zsh, use the full power of the language.

Core Principle

If it spawns a subprocess, there's a zsh builtin for it. Every grep, sed, awk, cut, tr, wc, cat, stat, date, and find invocation in a zsh script is a missed opportunity. Zsh has native equivalents that are faster and compose better.

The Anti-Pattern Table

Stop writing bash with a zsh shebang. These are the most common mistakes:

Instead of (bash-ism)	Use (idiomatic zsh)	Why
echo "text"	print "text"	print has -P (prompt colors), -f (printf), -l (per-line), -C (columns)
echo "$str" | tr '[:lower:]' '[:upper:]'	${(U)str}	Parameter expansion flag, no subprocess
echo "$str" | sed 's/foo/bar/g'	${str//foo/bar}	Native substitution
echo "$str" | grep -o 'pattern'	${(M)str:#pattern} or [[ $str =~ pattern ]] && print $MATCH	Pattern matching, no subprocess
echo "$str" | cut -d, -f2	${${(s:,:)str}[2]}	Split + index
echo "$str" | wc -l	${#${(f)str}}	Split on newlines + count
cat file.txt	$(<file.txt)	No subprocess at all
declare -A assoc	typeset -A assoc or local -A assoc	typeset is the zsh native
${!varname} (indirect)	${(P)varname}	(P) flag for indirection
${BASH_REMATCH[1]}	$match[1]	Zsh uses $MATCH and $match array
read -a arr	read -A arr	-A for array in zsh
arr[0] (first element)	arr[1]	Zsh arrays are 1-indexed
find . -name "*.log" -mtime -1	**/*.log(.m-1)	Glob qualifiers replace find entirely
stat -c %s file	zstat +size file	zsh/stat module, no subprocess
date +%s	$EPOCHSECONDS	zsh/datetime module
getopts / getopt	zparseopts	Native, supports long opts, fills arrays

Script Template

Start every zsh script with this foundation:

#!/usr/bin/env zsh
setopt ERR_EXIT NO_UNSET PIPE_FAIL
setopt EXTENDED_GLOB

# Load modules as needed:
# zmodload zsh/zutil      # zparseopts (usually auto-loaded)
# zmodload zsh/datetime    # $EPOCHSECONDS, strftime
# zmodload zsh/stat        # zstat for file metadata
# zmodload -F zsh/stat b:zstat  # selective: only zstat builtin
# zmodload zsh/mathfunc    # sin, cos, sqrt, floor, ceil, abs
# zmodload zsh/mapfile     # read/write files via $mapfile assoc array
# zmodload zsh/pcre        # Perl-compatible regexes

Note: setopt ERR_EXIT NO_UNSET PIPE_FAIL is the zsh equivalent of bash's set -euo pipefail. Use the long option names — they're self-documenting and case/underscore insensitive.

The 10 Most Impactful Features

1. Parameter Expansion Flags

Compose with ${(flags)var}. The most useful: (f) split on newlines, (s:sep:) split on separator, (j:sep:) join, (U) uppercase, (L) lowercase, (u) unique, (o) sort, (k) keys, (v) values, (q) quote, (P) indirect.

See references/param-expansion.md for the full flag table and composition examples.

2. zparseopts

Native argument parsing that fills zsh arrays directly. Supports long options, boolean flags, required/optional arguments. Never use getopts, getopt, or manual while-shift loops.

See references/zparseopts.md for the full API and patterns.

3. print Builtin

Replace echo and printf everywhere. Key flags: -P for prompt-style colors (%F{red}, %B), -f for printf formatting, -l for one-per-line, -C n for n columns, -r for raw output, -v name to store in variable.

See references/print-and-output.md for all flags and patterns.

4. Glob Qualifiers

Append (qualifiers) to any glob pattern. (.) plain files, (/) directories, (N) nullglob (no error if empty), (om) sort by mtime, (Lm+10) larger than 10MB, (m-1) modified in last day. Composable. Replaces find entirely.

See references/glob-qualifiers.md for the full qualifier table.

5. Anonymous Functions

() { body } args — immediately-invoked, scoped. Use for local variable isolation in scripts and .zshrc. No function name pollution.

6. Always Blocks

{ try } always { cleanup } — zsh's try-finally. The always block runs regardless of errors, return, or break. Use for guaranteed cleanup (temp files, locks, traps).

7. Associative Arrays

typeset -A map=(key1 val1 key2 val2). Access keys with ${(k)map}, values with ${(v)map}, both with ${(kv)map}. Check existence with [[ -v map[key] ]]. 1-indexed like all zsh arrays.

8. String Operations Without Subprocesses

Pattern removal (${var##*/}, ${var%.*}), substitution (${var//old/new}), splitting (${(s:,:)var}), filtering (${(M)array:#pattern}). Replaces sed, awk, cut, tr, grep.

See references/string-ops.md for the complete replacement table.

9. Modules

Load with zmodload. The essential ones: zsh/datetime (timestamps without date), zsh/stat (file metadata without stat), zsh/mathfunc (floating-point math without bc), zsh/mapfile (file I/O without cat), zsh/pcre (Perl regexes).

See references/modules.md for all modules with examples.

10. $(<file) File Reading

$(<file) reads a file's contents without spawning cat. Note: trailing newlines are stripped (same as command substitution). Combine with (f) to get an array of lines: lines=("${(@f)"$(<file)"}").

Common Patterns

CLI Tool Pattern

main() {
  local -a flag_help flag_verbose
  local -a arg_output
  zparseopts -D -E -F -- \
    {h,-help}=flag_help \
    {v,-verbose}=flag_verbose \
    {o,-output}:=arg_output \
    || { print -P "%F{red}Invalid options%f"; return 1 }

  (( $#flag_help )) && { usage; return 0 }

  local verbose=$(( $#flag_verbose > 0 ))
  local output=${arg_output[-1]:-/dev/stdout}
  local -a positional=("$@")  # remaining args after -D

  # ... rest of logic
}

usage() {
  print -rC1 -- \
    "Usage: ${0:t} [options] <args>" \
    "" \
    "Options:" \
    "  -h, --help       Show this help" \
    "  -v, --verbose    Verbose output" \
    "  -o, --output F   Output file"
}

main "$@"

Colored Output Pattern

msg()  { print -P "%F{blue}==>%f %B${1//%/%%}%b" }
warn() { print -P "%F{yellow}warning:%f ${1//%/%%}" >&2 }
err()  { print -P "%F{red}error:%f ${1//%/%%}" >&2 }
die()  { err "$1"; return ${2:-1} }  # return + ERR_EXIT = script exits

File Processing Without External Tools

() {
  local -a lines=("${(@f)"$(<$1)"}")
  local -a matches=(${(M)lines:#*ERROR*})
  print -l "Found ${#matches} errors:" $matches
} /var/log/app.log

Temp File with Guaranteed Cleanup

{
  local tmpfile=$(mktemp)
  process_data > $tmpfile
  use_result < $tmpfile
} always {
  [[ -f $tmpfile ]] && rm -f $tmpfile
}

Reference Files

Detailed documentation for each major feature area:

• references/param-expansion.md — All 40+ parameter expansion flags with composition
• references/zparseopts.md — Full API, spec format, patterns, gotchas
• references/print-and-output.md — print flags, prompt expansion, zformat
• references/glob-qualifiers.md — Complete qualifier table, replacing find
• references/string-ops.md — Replacing grep, sed, awk, cut, tr with pure zsh
• references/modules.md — zsh/datetime, zsh/stat, zsh/mapfile, zsh/mathfunc, zsh/pcre, zsh/zutil