checking if parameter passed is a number

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# 1  
checking if parameter passed is a number

I have written a function that fills an array and another function where if a parameter is supplied it will jump to that part of the array and cat it to the screen.

I need to put in some checks to make sure the parameter supplied is firstly a number and then not a number great than the length of the array. if the user enters no value or anincorrect value it should be ignored and just cats out the entire array.

any ideas?
# 2  
set -A myarr a b hello bye

echo "Enter a number \c"
read var
b=$(echo $var | tr -dc '[0-9]')
if [[ ${#b} -eq ${#var} || $var -le  ${#myarr[*]} ]]; then
   echo "$var is not all numeric characters or too large"

# 3  
Check this...

read Input
[[ "$Input" == ?(+|-)+([0-9]) ]] && echo "$Input is numeric" 


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