Bash check if array of variables have values or not

Question

I have an array of variables. I want to check if the variables have a value using the for loop.

I am getting the values into loop but the if condition is failing

function check {
    arr=("$@")
    for var in "${arr[@]}"; do
        if [ -z $var ] ; then
            echo $var "is not available"
        else
            echo $var "is available"
        fi
    done
}

name="abc"
city="xyz"
arr=(name city state country)
check ${arr[@]}

For the above I am getting all as available

Expected output is

name is available
city is available
state is not available
country is not available

var in your loop takes on the values name, city, state and country. [ -z ... ] tests whether the length of the argument is zero. None of those words has zero length, so the else branch is taken every time. — user1934428
– user1934428, Commented Feb 28, 2020 at 11:42

Ivan · Accepted Answer · 2020-02-28 10:44:59Z

4

This is the correct syntax for your task

if [ -z "${!var}" ] ; then
    echo $var "is not available"
else
    echo $var "is available"
fi

Explanation, this method uses an indirect variable expansion, this construction ${!var} will expand as value of variable which name is in $var.

Changed check function a bit

check () {
    for var in "$@"; do
        [[ "${!var}" ]] && not= || not="not "
        echo "$var is ${not}available"
    done
}

And another variant using declare

check () {
    for var in "$@"; do
        declare -p $var &> /dev/null && not= || not="not "
        echo "$var is ${not}available"
    done
}

From declare help

$ declare --help
declare: declare [-aAfFgilnrtux] [-p] [name[=value] ...]
    Set variable values and attributes.
    Declare variables and give them attributes.  If no NAMEs are given,
    display the attributes and values of all variables.
    ...
    -p  display the attributes and value of each NAME
    ...

Actually all vars can be checked at once using this

check () {
    declare -p $@ 2>&1 | sed 's/.* \(.*\)=.*/\1 is available/;s/.*declare: \(.*\):.*/\1 is not available/'
}

edited Feb 28, 2020 at 10:44

answered Feb 28, 2020 at 9:42

Ivan

7,5111 gold badge22 silver badges27 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Fazlin Over a year ago

It would be great if you can explain the change.

bob dylan Over a year ago

-z string True if the length of string is zero.

KamilCuk Over a year ago

This has a bug - variables with values with spaces will result in an error message from test.

Ivan Over a year ago

If space isn't valid value than it's not a bug it's a feature)

Ivan Over a year ago

And i just followed OPs style

kvantour · Accepted Answer · 2020-02-28 10:53:36Z

0

While indirection is a possible solution, it is not really recommended to use. A safer way would be to use an associative array:

function check {
    eval "declare -A arr="${1#*=}
    shift
    for var in "$@"; do
        if [ -z "${arr[$var]}" ] ; then
            echo $var "is not available"
        else
            echo $var "is available"
        fi
    done
}

declare -A list
list[name]="abc"
list[city]="xyz"

check "$(declare -p list)" name city state country

This returns:

name is available
city is available
state is not available
country is not available

The following question was used to create this answer: How to rename an associative array in Bash?

answered Feb 28, 2020 at 10:53

kvantour

26.9k4 gold badges57 silver badges81 bronze badges

Comments

fozzybear · Accepted Answer · 2024-03-20 14:23:14Z

For newer Bash versions (I think ~4.3), there's no need to use eval or any other abundant code.

Checking, if an array has any contents, is as simple as:

if [[ ${array[@]} ]]; then
    echo -e "Array has ${#array[@]} elements"
fi

Any whitespace elements will also count as content here; to ignore them, one could either use a whitespace-negating RegEx in the condition test, or iterate over the array and check each element.

There's also the possibility to use named references, to avoid superfluous array value copying and expansions, when passing arrays as arguments to functions:

declare -a emptyArray
declare -a array=( TEST1 TEST2 TEST3 )
declare -a onlyBlanksArray=('   ' ' ' '  ')
declare -a withBlanksArray=('   ' ' 1 ' '  ')

# Checks if an array has blank/non-blank elements (is non-empty)
has_elements() {
    local -n aRef="$1"
    [[ ${aRef[@]} ]]
}

# Checks if an array contains only blank elements
has_only_blanks() {
    local -n aRef="$1"
    [[ ${aRef[@]} == +([[:space:]]) ]]
}

if has_elements array; then
    echo -e "Array has ${#array[@]} elements"
fi

if ! has_elements emptyArray; then
    echo -e "ARRAY IS EMPTY"
fi

if has_only_blanks onlyBlanksArray; then
    echo -e "Is blanks-only array"
fi

if ! has_only_blanks withBlanksArray; then
    echo -e "ARRAY CONTAINS NON-BLANK ELEMENTS"
fi

Collectives™ on Stack Overflow

Bash check if array of variables have values or not

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related