Test if element is in array in bash

Question

Is there a nice way of checking if an array has an element in bash (better than looping through)?

Alternatively, is there another way to check if a number or string equals any of a set of predefined constants?

Answer 1

In Bash 4, you can use associative arrays:

# set up array of constants
declare -A array
for constant in foo bar baz
do
    array[$constant]=1
done

# test for existence
test1="bar"
test2="xyzzy"

if [[ ${array[$test1]} ]]; then echo "Exists"; fi    # Exists
if [[ ${array[$test2]} ]]; then echo "Exists"; fi    # doesn't

To set up the array initially you could also do direct assignments:

array[foo]=1
array[bar]=1
# etc.

or this way:

array=([foo]=1 [bar]=1 [baz]=1)

Answer 2

There is a way to test if an element of an associative array exists (not set), this is different from empty:

isNotSet() {
    if [[ ! ${!1} && ${!1-_} ]]
    then
        return 1
    fi
}

Then use it:

declare -A assoc
KEY="key"
isNotSet assoc[${KEY}]
if [ $? -ne 0 ]
then
  echo "${KEY} is not set."
fi

Answer 3

It's an old question, but I think what is the simplest solution has not appeared yet: test ${array[key]+_}. Example:

declare -A xs=([a]=1 [b]="")
test ${xs[a]+_} && echo "a is set"
test ${xs[b]+_} && echo "b is set"
test ${xs[c]+_} && echo "c is set"

Outputs:

a is set
b is set

To see how this work check this.

Answer 4

I don't think you can do it properly without looping unless you have very limited data in the array.

Here is one simple variant, this would correctly say that "Super User" exists in the array. But it would also say that "uper Use" is in the array.

MyArray=('Super User' 'Stack Overflow' 'Server Fault' 'Jeff' );
FINDME="Super User"

FOUND=`echo ${MyArray[*]} | grep "$FINDME"`

if [ "${FOUND}" != "" ]; then
  echo Array contains: $FINDME
else
  echo $FINDME not found
fi

#
# If you where to add anchors < and > to the data it could work
# This would find "Super User" but not "uper Use"
#

MyArray2=('<Super User>' '<Stack Overflow>' '<Server Fault>' '<Jeff>' );

FOUND=`echo ${MyArray2[*]} | grep "<$FINDME>"`

if [ "${FOUND}" != "" ]; then
  echo Array contains: $FINDME
else
  echo $FINDME not found
fi

The problem is that there is no easy way to add the anchors (that I can think of) besides looping through the array. Unless you can add them before you put them in the array...