How to fix For Loop and If condition NOT working in Bash Script

Question

I have that For Loop with If condition but it's Not working correctly. It supposes to check each index value if < 255 display Valid else Not Valid. The third and Forth are not correct.

How to fix that issue?

listNumber=(25 255 34 55)
listLength=${#listNumber[@]}
isValid=0

for ((index=0; index<$listLength; index++)); do
    itemNumber="$((index+1))"
    
    if [[ ${listNumber[$index]} < 255 ]]; then
        echo -e "Item $itemNumber : ${listNumber[$index]} is Valid. \n"
        isValid=1
    else
        echo -e "Item $itemNumber : ${listNumber[$index]} is NOT Valid. \n"
    fi
done

Result:
Item 1 : 25 is Valid. 

Item 2 : 255 is NOT Valid. 

Item 3 : 34 is NOT Valid. 

Item 4 : 55 is NOT Valid.

Ionuț G. Stan · Accepted Answer · 2022-03-25 14:58:45Z

1

Unfortunately, < when used inside [[...]] will use string comparison:

When used with [[, the ‘<’ and ‘>’ operators sort lexicographically using the current locale.

Source: https://www.gnu.org/software/bash/manual/bash.html#index-commands_002c-conditional

You either use the appropriate arithmetic comparison operator, which is -lt in this case:

if [[ ${listNumber[$index]} -lt 255 ]]; then
fi

Or use an arithmentic context for the condition, which is denoted using double parentheses (similar to how you've written the for loop):

if (( ${listNumber[$index]} < 255 )); then
fi

edited Mar 25, 2022 at 14:58

answered Mar 25, 2022 at 14:53

Ionuț G. Stan

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2 Comments

Bruce Q. Over a year ago

Thanks a lot! Appreciate your help :)

Ionuț G. Stan Over a year ago

@BruceQ. happy to help :)

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