<<Anchor(faq46)>>
== I want to check to see whether a word is in a list (or an element is a member of a set). ==
If your real question is ''How do I check whether one of my parameters was -v?'' then see [[BashFAQ/035|FAQ #35]] instead. Otherwise, read on…

<<TableOfContents>>
=== Associative arrays ===
All we need to do is create an entry for each item and look it up by index. In this example, we test whether the user input `x` is a member of the set `a`:

{{{
# Bash etc.

function get_input {
	[[ -t 0 ]] || return
	printf 'hm? '
	IFS= read -r${BASH_VERSION+\e} -- "$1"
}

set -- Bigfoot UFOs Republicans
typeset -A a
for x; do
	a+=([$x]=)
done

get_input x

if [[ -v a[$x] ]]; then
	printf '%s exists!\n' "$x"
else
	printf $'%s doesn\'t exist.\\n' "$x"
fi
}}}

=== Indexed arrays ===
We can store a list of strings in an indexed array by looping over each element:

{{{
# Bash

typeset -a haystack
for x in "${haystack[@]}"; do
	[[ $x == "$needle" ]] && printf 'Found %q!\n' "$needle"
done
}}}

=== enum (ksh93) ===
In ksh93t or later, one may create enum types/variables/constants using the `enum` builtin. These work similarly to C enums (and the equivalent feature of other languages). These may be used to restrict which values may be assigned to a variable so as to avoid the need for an expensive test each time an array variable is set or referenced. Like types created using `typeset -T`, the result of an `enum` command is a new declaration command that can be used to instantiate objects of that type.

{{{
# ksh93

 $ enum colors=(red green blue)
 $ colors foo=green
 $ foo=yellow
ksh: foo:  invalid value yellow
}}}

`typeset -a` can also be used in combination with an enum type to allow enum constants as subscripts.

{{{
# ksh93

 $ typeset -a '[colors]' bar
 $ bar[blue]=test1
 $ typeset -p bar
typeset -a '[colors]' bar=([blue]=test)
 $ bar[orange]=test
ksh: colors:  invalid value orange
}}}

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CategoryShell