zsh-cheatsheet.md

ZSH CheatSheet

This is a cheat sheet for how to perform various actions to ZSH, which can be tricky to find on the web as the syntax is not intuitive and it is generally not very well-documented.

Strings

Description	Syntax
Get a single character	${VARNAME[index]}
Get the string from a specific index	${VARNAME[index,-1]}
Get a substring	${VARNAME[from,to]}
Replace the first occurrence in a string	${VARNAME/toreplace/replacement}
Replace all occurrences in a string	${VARNAME//toreplace/replacement}
Cut a string after a model	${VARNAME%%model*}
Check if a string starts by a specific substring	if [[ $VARNAME = "startstr"* ]]

Arrays

Description	Syntax
Create an array	VARNAME=()
Create an array with initial values	VARNAME=(value1 value2 value3)
Push to an array	VARNAME+=(value)
Access an array's element	VARNAME[index]
Remove first element from an array (shift)	shift VARNAME
Remove last element from an array (pop)	shift -p VARNAME
Get an array's length	${#VARNAME}
Iterate over an array's values	for value in $VARNAME;
Get index of a value in an array	${VARNAME[(i)value]}
Get an array slice after the specified index	${VARNAME:index}
Get an array slice after the specified index	${VARNAME:index:length}
Check if a value is contained in an array	if (( ${VARNAME[(i)value]} <= ${#VARNAME} ));
Check if an array is empty	if [[ -z $VARNAME ]]
Check if an array is not empty	if [[ ! -z $VARNAME ]]

Associative arrays (= maps / dictionaries)

Associate arrays are the equivalent of hash maps or dictionaries in many other programming languages: unlike arrays, they can use string keys, and these don't necessary have an order.

Description	Syntax
Create an associative array	typeset -A VARNAME=()
Create an associative array with initial values	typeset -A VARNAME=( [key1]=value1 [key2]=value2 )
Add a new key to the array	VARNAME[key]=value
Access the array's elements	$VARNAME[key]
Remove a key from the array	unset 'VARNAME[key]
Get the array's number of elements	${#VARNAME}
Iterate over the array's values	for value in $VARNAME;
Iterate over the array's keys	for key in ${(k)VARNAME};
Iterate over the array's key-value pairs	for key value in ${(kv)VARNAME};

Arithmetics

Description	Syntax
Compute a mathematical expression (variables don't need to be prefixed with $ in it)	$((expression))

Variables

Description	Syntax
Get the value of a variable whose name is in another variable	${(P)NAMEVAR}
Get the list of all defined variables, as an array	${(k)parameters}
Delete a variable	unset VARNAME

Functions

Description	Syntax
Declare a local variable (not accessible outside the function)	local varname=...
Get the original executable name	$0
Get a parameter	$1 (second is $2, etc.)
Expand all parameters	$*
Expand all parameters but keep them quoted if needed	$@ (tip: it's an array!)
Get the number of parameters (so not counting $0)	$#
Remove the first parameter from $@	shift
Remove the last parameter from $@	shift -p
Exit the function with a status code (behaves like for a command)	return 1 (or any other code)
Get the list of all functions, as an array	${(k)functions}
Delete a function	unset -f func_name

Aliases

Description	Syntax
Display the list of all defined aliases	alias
Get the list of all defined aliases, as an array	${(k)aliases}
Define an alias	alias name="command arg1 arg2 arg3 ..."
Remove an alias	unalias name
Get the arguments, with escaped spaces	${@:q}

Conditionals

A word on conditionals

Syntaxes:

# 1)
if expression
then
    # instructions
fi

# 2)
if expression; then
    # instructions
fi

# 3)
if expression; then ...; fi

# 4)
if expression; then
    # instructions
else
    # instructions
fi

# 5)
if expression; then
    # instructions
elif expression
    # instructions
else
    # instructions
fi

Description	Syntax
Check if a string is empty or not defined	if [[ -z $VARNAME ]];
Check if a string is defined and not empty	if [[ ! -n $VARNAME ]];
Check if a file exists	if [[ -f "filepath" ]];
Check if a directory exists	if [[ -d "dirpath" ]];
Check if a symbolic link exists	if [[ -L "symlinkpath" ]];
Check if a shell option is set	if [[ -o OPTION_NAME ]];
Check if two values are equal	if [[ $VAR1 = $VAR2 ]];
Check if two values are different	if [[ $VAR1 != $VAR2 ]];
Check if a number is greater than another	if (( $VAR1 > $VAR2 ));
Check if a number is smaller than another	if (( $VAR1 < $VAR2 ));
Check if a command exits successfully (exit code 0)	if command arg1 arg2 ...
Check if a command doesn't exit successfully (exit code != 0)	if ! command arg1 arg2 ...

Note that the $ symbol preceding variables' names in arithmetic expression (((...))) are purely optional, so you can perfectly write if (( VAR1 < VAR2 )); for instance.

You can read all dash - options in ZSH's manual, as there are many different ones: http://zsh.sourceforge.net/Doc/Release/Conditional-Expressions.html

Loops

Syntaxes:

# 1)
for itervarname in iterable
do
    # instructions
done

# 2)
for itervarname in iterable; do
    # instructions
done

# 3)
for itervaname in iterable; do ...; done

Description	Syntax
Iterate over a range (inclusive)	for i in {from..to};
Iterate over a list of filesystem items	for i in globpattern;
Iterate over a list of filesystem items, fail silently if no match found	for i in globpattern(N);

Examples cheat sheet

Return a value from within a function:

function add() {
    local sum=$(($1 + $2))
    echo $sum
}

function add_twice() {
    local sum=$(add $1 $2) # get the callee's STDOUT
    local sum_twice=$(add $sum $sum)
    echo $sum_twice
}

echo $(add 2 3) # 5
echo $(add_twice 2 3) # 10

A word on conditionals

Conditionals use expressions, such as in if [[ -z $VARNAME ]]; the expression is [[ -z $VARNAME ]]. These can also be used in while loops, as well as be used outside of blocks:

[[ -z $VARNAME ]] && echo "VARNAME is not defined or empty!"
[[ -f $FILEPATH ]] && echo "File exists!"

This works because conditional expressions ([[ ... ]] and (( ... ))) don't actually return a value; they behave like commands and as such set the status code to 0 if the condition is true, or 1 else.

If we want to display the message only if the condition is falsey:

[[ -z $VARNAME ]] || echo "VARNAME is not empty!"
[[ -f $FILEPATH ]] || echo "File does not exist!"