Zsh Expert

Zsh Scripting Expert

Reference skill for Zsh syntax and idioms. Provides accurate, practical explanations when the user asks about Zsh-specific constructs.

Trigger

Automatically activate when:

• The user asks about Zsh parameter expansions, array operations, glob qualifiers, or other Zsh-specific syntax
• Code containing Zsh-specific constructs like ${(...)} or (( )) is being discussed
• Questions like "How do I ... in Zsh" or "What does this Zsh syntax do"
• Questions about differences between Bash and Zsh

Response Style

• Respond in the same language the user uses (English or Japanese)
• Start with a concise 1-2 line explanation of the syntax, then provide concrete examples
• Highlight differences from Bash when relevant
• Reference real examples from the zplug codebase with file paths and line numbers when applicable

Reference: Zsh Parameter Expansion

Basic Forms

String Manipulation

Parameter Expansion Flags (Zsh-specific)

Used as ${(flags)var}. Multiple flags can be combined.

Array Filtering

Reference: Array Operations

Basics

# Declaration
typeset -a arr=(one two three)

# Zsh is 1-indexed (Bash is 0-indexed)
echo $arr[1]          # one
echo $arr[-1]         # three (last element)

# Slicing
echo $arr[2,3]        # two three
echo $arr[2,-1]       # two three (from 2nd onward)

# Element count
echo $#arr            # 3
echo ${#arr[@]}       # 3

# Append
arr+=("four")
arr[5]="five"         # gaps filled with empty strings

# Delete (specific index)
arr[2]=()             # removes 2nd element and shifts

# Iterate all elements
for x in "${arr[@]}"; do echo $x; done

# Iterate with index
for i in {1..$#arr}; do echo "$i: $arr[$i]"; done

Associative Arrays

typeset -A hash
hash=(key1 val1 key2 val2)
# or
hash[key1]=val1

echo $hash[key1]        # val1
echo ${(k)hash}          # key1 key2 (keys)
echo ${(v)hash}          # val1 val2 (values)
echo ${(kv)hash}         # key1 val1 key2 val2

# Check key existence
(( ${+hash[key1]} )) && echo "exists"

# Element count
echo ${#hash}            # 2

Reference: Globbing

Extended Glob (setopt EXTENDED_GLOB)

Glob Qualifiers

Used as pattern(qualifier). Filter files by attributes.

# Example: .zsh files under current dir, sorted by mtime
print -l **/*.zsh(.om)

# Example: regular files modified within 7 days
print -l *(m-7.)

Reference: Conditionals & Arithmetic

[[ ]] Conditional Expressions

[[ -n $var ]]          # Non-empty check
[[ -z $var ]]          # Empty check
[[ $a == $b ]]         # String equality
[[ $a != $b ]]         # String inequality
[[ $a =~ regex ]]      # Regex match (results in MATCH, match)
[[ $a == pattern ]]    # Glob pattern match
[[ -e $file ]]         # File exists
[[ -d $dir ]]          # Is a directory
[[ -f $file ]]         # Is a regular file
[[ -L $file ]]         # Is a symbolic link
[[ -x $file ]]         # Is executable

Zsh-specific: == supports glob pattern matching inside [[ ]]. PCRE is available with =~ when setopt RE_MATCH_PCRE is set.

(( )) Arithmetic Expressions

(( x = 5 + 3 ))        # Assignment
(( x++ ))               # Increment
(( x > 0 )) && echo positive
(( result = a > b ? a : b ))  # Ternary operator

Reference: Zsh-Specific Builtins

Reference: Useful Options

Reference: Hooks & Traps

# precmd: runs just before each prompt display
add-zsh-hook precmd my_precmd_func

# preexec: runs just before command execution (arg: command string)
add-zsh-hook preexec my_preexec_func

# chpwd: runs on directory change
add-zsh-hook chpwd my_chpwd_func

# zshexit: runs on shell exit
add-zsh-hook zshexit my_cleanup_func

# TRAPINT: Ctrl+C handler
TRAPINT() { print "interrupted"; return 128+2; }

# TRAPERR: error handler
TRAPERR() { print "error: $?" >&2; }

# TRAPZERR: non-zero exit handler (equivalent to TRAPERR)

Reference: Anonymous Functions

# Immediately-invoked function (creates scope)
() {
    local tmp="scoped"
    echo $tmp
}

# With arguments
() {
    echo "arg1=$1 arg2=$2"
} "hello" "world"

Reference: Key Differences from Bash

Reference: ZLE (Zsh Line Editor)

# Custom widget
my-widget() {
    BUFFER="modified"
    CURSOR=$#BUFFER
}
zle -N my-widget
bindkey '^X^M' my-widget

# Key variables
# BUFFER  — current input line
# CURSOR  — cursor position
# LBUFFER — text left of cursor
# RBUFFER — text right of cursor
# WIDGET  — name of currently executing widget

Answer Guidelines

1. Start with a concise 1-2 line explanation of the syntax in question
2. Provide concrete code examples (minimal and runnable)
3. Note any gotchas or common pitfalls
4. Reference real usage in the zplug codebase when applicable, using base/path/file.zsh:NN format
5. For users coming from Bash, explicitly highlight the differences
6. List related syntax or flags under a "See also" section when relevant