Check if an element is present in a Bash array
ArraysBashShellSearchArrays Problem Overview
I was wondering if there is an efficient way to check if an element is present within an array in Bash? I am looking for something similar to what I can do in Python, like:
arr = ['a','b','c','d']
if 'd' in arr:
do your thing
else:
do something
I've seen solutions using associative array for bash for Bash 4+, but I am wondering if there is another solution out there.
Please understand that I know the trivial solution is to iterate in the array, but I don't want that.
Arrays Solutions
Solution 1 - Arrays
You could do:
if [[ " ${arr[*]} " == *" d "* ]]; then
echo "arr contains d"
fi
This will give false positives for example if you look for "a b" -- that substring is in the joined string but not as an array element. This dilemma will occur for whatever delimiter you choose.
The safest way is to loop over the array until you find the element:
array_contains () {
local seeking=$1; shift
local in=1
for element; do
if [[ $element == "$seeking" ]]; then
in=0
break
fi
done
return $in
}
arr=(a b c "d e" f g)
array_contains "a b" "${arr[@]}" && echo yes || echo no # no
array_contains "d e" "${arr[@]}" && echo yes || echo no # yes
Here's a "cleaner" version where you just pass the array name, not all its elements
array_contains2 () {
local array="$1[@]"
local seeking=$2
local in=1
for element in "${!array}"; do
if [[ $element == "$seeking" ]]; then
in=0
break
fi
done
return $in
}
array_contains2 arr "a b" && echo yes || echo no # no
array_contains2 arr "d e" && echo yes || echo no # yes
For associative arrays, there's a very tidy way to test if the array contains a given key: The -v
operator
$ declare -A arr=( [foo]=bar [baz]=qux )
$ [[ -v arr[foo] ]] && echo yes || echo no
yes
$ [[ -v arr[bar] ]] && echo yes || echo no
no
See 6.4 Bash Conditional Expressions in the manual.
Solution 2 - Arrays
Obvious caveats aside, if your array was actually like the one above, you could do
if [[ ${arr[*]} =~ d ]]
then
do your thing
else
do something
fi
Solution 3 - Arrays
-
Initialize array
arr
and add elements -
set variable to search for
SEARCH_STRING
-
check if your array contains element
arr=() arr+=('a') arr+=('b') arr+=('c')
SEARCH_STRING='b'
if [[ " ${arr[*]} " == "$SEARCH_STRING" ]]; then echo "YES, your arr contains $SEARCH_STRING" else echo "NO, your arr does not contain $SEARCH_STRING" fi
Solution 4 - Arrays
If array elements don't contain spaces, another (perhaps more readable) solution would be:
if echo ${arr[@]} | grep -q -w "d"; then
echo "is in array"
else
echo "is not in array"
fi
Solution 5 - Arrays
array=("word" "two words") # let's look for "two words"
##using grep
and printf
:
(printf '%s\n' "${array[@]}" | grep -x -q "two words") &&
##using for
:
(for e in "${array[@]}"; do [[ "$e" == "two words" ]] && exit 0; done; exit 1) &&
For not_found results add || <run_your_if_notfound_command_here>
Solution 6 - Arrays
As bash does not have a built-in value in
array operator and the =~
operator or the [[ "${array[@]" == *"${item}"* ]]
notation keep confusing me, I usually combine grep
with a here-string:
colors=('black' 'blue' 'light green')
if grep -q 'black' <<< "${colors[@]}"
then
echo 'match'
fi
Beware however that this suffers from the same false positives issue as many of the other answers that occurs when the item to search for is fully contained, but is not equal to another item:
if grep -q 'green' <<< "${colors[@]}"
then
echo 'should not match, but does'
fi
If that is an issue for your use case, you probably won't get around looping over the array:
for color in "${colors[@]}"
do
if [ "${color}" = 'green' ]
then
echo "should not match and won't"
break
fi
done
for color in "${colors[@]}"
do
if [ "${color}" = 'light green' ]
then
echo 'match'
break
fi
done
Solution 7 - Arrays
Here's another way that might be faster, in terms of compute time, than iterating. Not sure. The idea is to convert the array to a string, truncate it, and get the size of the new array.
For example, to find the index of 'd':
arr=(a b c d)
temp=`echo ${arr[@]}`
temp=( ${temp%%d*} )
index=${#temp[@]}
You could turn this into a function like:
get-index() {
Item=$1
Array="$2[@]"
ArgArray=( ${!Array} )
NewArray=( ${!Array%%${Item}*} )
Index=${#NewArray[@]}
[[ ${#ArgArray[@]} == ${#NewArray[@]} ]] && echo -1 || echo $Index
}
You could then call:
get-index d arr
and it would echo back 3, which would be assignable with:
index=`get-index d arr`
Solution 8 - Arrays
FWIW, here's what I used:
expr "${arr[*]}" : ".*\<$item\>"
This works where there are no delimiters in any of the array items or in the search target. I didn't need to solve the general case for my applicaiton.