How do I test if an item is in a bash array?

Question

Help for a simple script

#!/bin/bash

array1=(
prova1
prova2
slack64
)

a="slack64"
b="ab"

if [ $a = $b ]
then
      echo "$a = $b : a is equal to b"
else
      echo "$a = $b: a is not equal to b"
fi

---

This script simply doesn't work, I want a script which check if slack64 is present in a list(i use an array),and simply give me, yes is present,or no. I don't know how to compare an array with a single variable.

Answer 1

Use a different kind of array: rather than an integer-indexed array, use an associative array, so the key (index) is what you will be checking for. bash-4.0 or later is required for this.

declare -A array1=( 
 [prova1]=1  [prova2]=1  [slack64]=1
)

a=slack64
[[ -n "${array1[$a]}" ]] && printf '%s is in array\n' "$a"

In the above we don't really care about the values, they need only be non-empty for this. You can "invert" an indexed array into a new associative array by exchanging the key and value:

declare -a array1=( 
 prova1 prova2 slack64
)
declare -A map    # required: declare explicit associative array
for key in "${!array1[@]}"; do map[${array1[$key]}]="$key"; done  # see below

a=slack64
[[ -n "${map[$a]}" ]] && printf '%s is in array\n' "$a"

This can pay off if you have large arrays which are frequently searched, since the implementation of associative arrays will perform better than array-traversing loops. It won't suit every use case though, since it cannot handle duplicates (though you can use the value as a counter, instead of just 1 as above), and it cannot handle an empty index.

Breaking out the complex line above, to explain the "inversion":

for key in "${!a[@]}"     # expand the array indexes to a list of words
do 
  map[${a[$key]}]="$key"  # exchange the value ${a[$key]} with the index $key
done

Answer 2

The straightforward way is to iterate with a loop :

var=ab
for item in "${array[@]}"; do
    [[ $var == "$item" ]] && echo "$var present in the array"
done

Answer 3

How to check if a Bash Array contains a value

---

False positive match

array=(a1 b1 c1 d1 ee)
[[ ${array[*]} =~ 'a' ]] && echo 'yes' || echo 'no'
output:
yes
[[ ${array[*]} =~ 'a1' ]] && echo 'yes' || echo 'no'
output:
yes
[[ ${array[*]} =~ 'e' ]] && echo 'yes' || echo 'no'
output:
yes
[[ ${array[*]} =~ 'ee' ]] && echo 'yes' || echo 'no'
output:
yes

Exact match

In order to look for an exact match, your regex pattern needs to add extra space before and after the value like (^|[[:space:]])"VALUE"($|[[:space:]])

# Exact match
array=(aa1 bc1 ac1 ed1 aee)
if [[ ${array[*]} =~ (^|[[:space:]])"a"($|[[:space:]]) ]]; then
    echo "Yes";
else
    echo "No";
fi
output:
No
if [[ ${array[*]} =~ (^|[[:space:]])"ac1"($|[[:space:]]) ]]; then
    echo "Yes";
else
    echo "No";
fi
output:
Yes
find="ac1"
if [[ ${array[*]} =~ (^|[[:space:]])"$find"($|[[:space:]]) ]]; then
    echo "Yes";
else
    echo "No";
fi
output:
Yes

For more usage examples the source of examples are here

Answer 4

With zsh:

array1=(
  prova1
  prova2
  slack64
)
a=slack64
if (( $array1[(Ie)$a] )); then
  printf '%s\n' "$a in array1"
fi

The I array subscript flag is for returning the index of the rightmost element that matches $a (or 0 if not found); with e, it's an exact / literal match, not pattern matching.

---

With bash:

Since bash's array members can't contain NUL bytes (contrary to zsh's), if you have GNU grep or compatible you can always do:

if (( ${#array1[@]} )) && printf '%s\0' "${array1[@]}" | grep -zqxFe "$a"; then
  printf '%s\n' "$a in array1"
fi

That is, print the elements NUL-delimited and ask grep to quietly find exact Fixed-string matches for the expression stored in $a in those zero-delimited records.

Answer 5

You can also use grep for that:

array1=(prova1 prova2 slack64)
a=slack64
if (printf '%s\n' "${array1[@]}" | grep -xq $a); then
    echo "it's in"
fi

Answer 6

This function works with associative arrays.

We can use this function to do one of the following:

-- check if the array has a certain key -----------------> inArray "myKey" ${!myArray[@]}"

-- check if the array contains a certain value ---------> inArray "myValue" "${myArray[@]}"

function inArray # ( keyOrValue, arrayKeysOrValues ) 
{
  local e
  for e in "${@:2}"; do 
    [[ "$e" == "$1" ]] && return 0; 
  done
  return 1
}

declare -A arr
arr[doo]=55

inArray "doo" "${!arr[@]}"
echo $?     # 0 
inArray "bla" "${!arr[@]}"
echo $?     # 1 
inArray "55" "${arr[@]}"
echo $?     # 0

Answer 7

You can use "grep".

_array=(a b c)
_find_me="b"
echo ${_array[@]} | grep "$_find_me" && 

    echo "I found: $_find_me"        || 

    echo "I could not found: $_find_me"

Output:

a b c
I found: b