check whether variable number or string

I am passing an argument to a file and i wanna check whether the argument is a number or string ?
how can i do this?

[[ -z $( echo $x | grep "^[0-9]*$" ) ]] || echo "number"

#/bin/ksh
a=$1
b=`echo $a| tr -dc  '[:digit:]' `
if [[ "$b" = "$a" ]] ; then
  echo "numbers only"
else
  echo "not numbers only"
fi

thanks it works

Had been answered many times, take a look at this