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2

Compare a variable that can have numeric or string as value

rated 0 times [ 2] [ 0] / answers: 1 / hits: 1517 / 1 Year ago, wed, january 25, 2023, 7:09:04

I have a variable named Seconds_Behind_Master from one of my scripts. The problem is that this variable can either have a numeric value or can also take a string NULL as its value. Now, when I try to execute this script in shell it gets executed but gives a warning like this:

[: Illegal number: NULL

I believe it is due to the fact that in this case the value is NULL but when it compares it with numeral value 60 it gives this warning. How can I rectify it?

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montwim

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2 Years ago

answered 1 Year ago gliroopy · Accepted Answer

In this case you should use an arithmetic evaluation - (( expression )):

if (( $Seconds_Behind_Master >= 60 )); then

    echo "replication delayed > 60."

elif [ "$Seconds_Behind_Master" = "NULL" ]; then

    echo "Delay is Null."

fi

If you want to respect the standard POSIX, then you can use:

if echo $Seconds_Behind_Master | egrep -q '^[0-9]+$' && [ "$Seconds_Behind_Master" -ge "60" ] ; then

    echo "replication delayed >= 60."

elif [ "$Seconds_Behind_Master" = "NULL" ]; then

    echo "Delay is Null."

fi

More about: Shell - Test a numeric variable.