Bash how to insert into array if the array does not contain the value within if statement

Question

I have a function to check if something is in an array:

function inArray() {
    local val="$1"
    shift
    local array=("$@")
    for i in "${array[@]}"; do
        if [ "${i}" == "${val}" ]; then
            return 0
        fi
    done
    return 1
}

And an if statement to try to insert values into noDupe only if it doesn't already have that value:

noDupe=()
values=("test" "test" "test2")
for value in ${values[@]}; do
    if [ $(inArray "${value}" "${values[@]}") -eq 1 ]; then
        noDupe+="{value}"
    fi
done

My current error is that -eq expects a unary operator. I've tried changing it to a == but that's just for strings and not the 0s and 1s my function is returning. How can I get the if statement to work?

Benjamin W. · Accepted Answer · 2020-08-03 03:07:01Z

1

Your function is using return values, but you're trying to use it as it if the return values were printed. The correct usage for "if the exit status is non-zero" simplifies to

if ! inArray "${value}" "${values[@]}"; then

Side note: the error you're getting is not that -eq expects a unary operator, it's

bash: [: -eq: unary operator expected

meaning that [ expected a unary operator, but instead it got -eq, a binary operator. This is because your command substitution is unquoted, and when the command returns nothing, your test becomes

[ -eq 1 ]

With proper quoting,

[ "$(inArray "${value}" "${values[@]}")" -eq 1 ]

the test would complain that it expects an integer expression (but gets the empty string instead), because it expands to

[ "" -eq 1 ]

answered Aug 3, 2020 at 3:07

Benjamin W.

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dash-o · Accepted Answer · 2020-08-03 03:26:03Z

1

The array search function can become a bottleneck if the array length is large. As an alternative consider using bash associative array. It will simplify the code, and speed up execution - reducing the complexity from O(n^2) to O(n log n).

The no-dup logic can be implemented without having to write the inArrayfunction.

declare -A v_temp
values=("test" "test" "test2")
for value in ${values[@]}; do
    v_temp[$value]=1
done
noDupe=(${!v_temp[@]})

answered Aug 3, 2020 at 3:26

dash-o

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Comments

Ivan · Accepted Answer · 2020-08-03 06:35:12Z

0

Consider this method using $BASH_REMATCH:

inArray () {
    re="_S_$1 | $1 | ${1}_E_"
    [[ "_S_${array[@]}_E_" =~ $re ]] && return 0 || return 1
}

And array name could be also send as arg to this function:

inArray () {
    name="$1[@]"
    re="_S_$2 | $2 | ${2}_E_"
    [[ "_S_${!name}_E_" =~ $re ]] && return 0 || return 1
}

edited Aug 3, 2020 at 6:35

answered Aug 3, 2020 at 6:27

Ivan

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