Changing array element value from within loop doesnt work as expected

Question

I have a shell script print function like below:

print_status()
{
 echo "$1|$2|$3|$4"
 paramArr=("$@")
 for i in "${#paramArr[@]}"
 do
   if [[ -z ${paramArr[i]} ]];
   then
       paramArr[i]="Unknown"
   fi
 done
 echo "${paramArr[*]}"
}

The function is supposed to print 4 values, with "|" as a delimiter. I have kept the print statement at the top of the function, just to show how the actual values to be printed.

I also wanted to check that each argument coming to this function, if is a blank value (i.e the variable actually contains nothing), then print "Unknown". I wanted to get this done via an array paramArr as above. But It doesn't work as expected.

Example :

Output1:
Running|162.103.172.46|3.345|-0.076
Running 162.103.172.46 3.345 -0.076 Unknown

Expected Output 1:
Running|162.103.172.46|3.345|-0.076
Running 162.103.172.46 3.345 -0.076 <-- With a "|" instead of space


Output2:
Not Running|||
Not Running    Unknown

Expected Output2:
Not Running|||
Not Running Unknown Unknown Unknown <-- With a "|" instead of space

What exactly is going wrong/missing in my function ?

for i in "${#paramArr[@]}" is a wrong construct, to loop over array elements — Inian
– Inian, Commented Feb 27, 2018 at 8:09

cdarke · Accepted Answer · 2018-02-27 07:58:56Z

1

You have several issues. First you are counting array indexes from zero to the number of elements. When that is 4 then you go from 0 - 4, which is 5 elements, so you get an extra one. When it is fewer than 4 then it won't add the 'Unknown' because you are not iterating far enough.

Second, when you print an array using [*] inside quotes, the delimiter between elements is the first character of $IFS, which by default is a space:

print_status()
{
    echo "$1|$2|$3|$4"
    paramArr=("$@")

    for ((i=0; i < 4; i++))
    do
        if [[ -z ${paramArr[i]} ]];
        then
            paramArr[i]="Unknown"
        fi
    done

    oldIFS="$IFS"
    IFS='|'
    echo "${paramArr[*]}"
    IFS="$oldIFS"
}

print_status Running 162.103.172.46 3.345 -0.076
print_status 'Not Running'

Gives:

Running|162.103.172.46|3.345|-0.076
Running|162.103.172.46|3.345|-0.076
Not Running|||
Not Running|Unknown|Unknown|Unknown

edited Feb 27, 2018 at 7:58

answered Feb 27, 2018 at 7:48

cdarke

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