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Bash Bits are small examples, tips and tutorials for Bash (Scripts). This bash bit shows you how find out if an array has an item.

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This is a simple function which helps you find out if an (non associative) array has an item. It allows you to call the function with just the array name, not ${arrayname[@]}. It returns 1 if the item is in the array, and 0 if it is not.

This is the function:

in_array() {
    local haystack=${1}[@]
    local needle=${2}
    for i in ${!haystack}; do
        if [[ ${i} == ${needle} ]]; then
            return 0
        fi
    done
    return 1
}

Now we can test it and see that it works:

declare -a vpsservers=("vps1" "vps2" "vps3" "vps4" "vps6");

in_array vpsservers vps3 && echo "found" || echo "not found"
in_array vpsservers vps5 && echo "found" || echo "not found"

Should return:

found
not found

Now a usage example. Lets say you have a script which requires a specific version of Ubuntu and does not work on other versions of ubuntu. You can use this to check if the version of ubuntu is supported with this function.

declare -a supported_ubuntu=("Ubuntu 10.04.1 LTS" "Ubuntu 10.04.3 LTS" "Ubuntu 10.04.4 LTS" "Ubuntu 10.10" "Ubuntu 12.04 LTS" "Ubuntu 12.04.1 LTS")

if [ -f "/etc/lsb-release" ]; then
    running_ubuntu=`awk -F "\"" '/DESCRIPTION/ { print $2 }' /etc/lsb-release`
    if in_array supported_ubuntu "${running_ubuntu}"; then
        echo "${running_ubuntu} is supported."
    else
        echo "${running_ubuntu} is not supported. Run ${0} again with the -f option to ignore this warning."
        exit 1
    fi
fi

Do note that forcing a specific version of something is not a best practice, however sometimes you are forced to.

Tags: array , bash , bash-bits , haystack , needle , shell , snippets