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.
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.
$seeking so that it's not considered a pattern.
-v operator only works in Bash 4.3+. In earlier versions, test for a key using +_: declare -A says says[horse]=neigh says[fish]= [[ ${says[horse]+_} ]] && echo "horse: ${says[horse]}" || echo "horse doesn't exist" horse: neigh [[ ${says[fish]+_} ]] && echo "fish: ${says[fish]}" || echo "fish doesn't exist" fish: [[ ${says[unicorn]+_} ]] && echo "unicorn: ${says[unicorn]}" || echo "unicorn doesn't exist" unicorn doesn't exist Tested in v4.2.46. SourceObvious 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
d will match xdy as well.
if [[ ${arr[*]} =~ $(echo '\<d\>') ]] (source)
arr and add elementsSEARCH_STRING 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
BASH_ARGV to test whether a certain word was given as an argument that requires a different one-off setup was present without having to do some kind of argparse which is overkill for this case.
If array elements don't contain spaces, another (perhaps more readable) solution would be:
if echo ${arr[@]} | grep -q -w "d"; then
echo "is in array"
else
echo "is not in array"
fi
-- to signal the end of parameters and negative number will not treated as a param for grep
array=("word" "two words") # let's look for "two words"
grep and printf:(printf '%s\n' "${array[@]}" | grep -x -q "two words") && <run_your_if_found_command_here>
for:(for e in "${array[@]}"; do [[ "$e" == "two words" ]] && exit 0; done; exit 1) && <run_your_if_found_command_here>
For not_found results add || <run_your_if_notfound_command_here>
grep -x... makes it the simplest to use.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
-x to grep to match the entire line.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 $Index
}
You could then call:
get-index d arr
and it would echo back 3, which would be assignable with:
index=`get-index d arr`
FWIW, here's what I used:
expr "${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.
bashto do what you want with a simple array.