Check for valid number in busybox?

Question

I am trying to do a script where i need to check if the user input is valid. I just can't figure it out. Have been trying different ways but can't find a solution. So if there are a busybox ash guru out there i am happy for all help.

if ! [[ $ANS =~ ^[0-9][.0-9]*$ ]]; then
    echo "abort"
else
    echo "go on"
fi

I want to see if the user inputs a number. A number with decimal is also allowed. If not then it should abort.

Same goes with..

if ! [[ $ANS =~ ^[0-9A-Fa-f]{6}$ ]] ; then
    echo "abort"
else
    echo "go on"
fi

Where i need it to see if hexadecimal is used. All i get is "unknown operand".

Answer 1

It feels a bit of a hack, but you can use egrep for this:

$ ANS=10.2
$ echo -n $ANS | egrep -q '^[0-9]*[.]?[0-9]*$' && echo success || echo failure
success
$ ANS=10.2.2
$ echo -n $ANS | egrep -q '^[0-9]*[.]?[0-9]*$' && echo success || echo failure
failure