Why can't I perform arithmetic on a variable received via curl?

Question

linux

For example:

#!/bin/bash

last_time_online=`curl -s "http://lolygirl.ru/time_online.php?client=clear"`
curr_date=`date +%s`
echo $(($curr_date - $last_time_online))

line 4: 1503766814 - 1503766801: syntax error: operand expected (erroneous label "1503766801")
Although if you take the curl output with handles and drive it in as a string, then everything works fine

Answer 1

in last_time_online after the last digit there is one more character, it must be cut off

last_time_online=`curl -s "http://lolygirl.ru/time_online.php?client=clear"`
last_time_online=${last_time_online:1:${#last_time_online}-1}
curr_date=`date +%s`
echo $(($curr_date - $last_time_online))