Check that a variable is a number in UNIX shell [duplicate]

Question

How do I check to see if a variable is a number, or contains a number, in UNIX shell?

Answer 1

if echo $var | egrep -q '^[0-9]+$'; then
    # $var is a number
else
    # $var is not a number
fi

Answer 2

Shell variables have no type, so the simplest way is to use the return type test command:

if [ $var -eq $var 2> /dev/null ]; then ...

(Or else parse it with a regexp)