BASH controllable bar

#!/bin/bash
######################################################################
#Copyright (C) 2018  Kris Occhipinti
#https://filmsbykris.com

#This program is free software: you can redistribute it and/or modify
#it under the terms of the GNU General Public License as published by
#the Free Software Foundation, either version 3 of the License, or
#(at your option) any later version.

#This program is distributed in the hope that it will be useful,
#but WITHOUT ANY WARRANTY; without even the implied warranty of
#MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#GNU General Public License for more details.

#You should have received a copy of the GNU General Public License
#along with this program.  If not, see <http://www.gnu.org/licenses/>.
######################################################################

let b=0

function main(){
  echo "Welcome..."
  sleep 1
  while [ 1 ]
  do
    let columns=$(tput cols)-10

    read -rsn1 x
    echo -n "="
    if [ "$x" = "a" ]
    then
      let b=$b-1
    elif [ "$x" = s ]
    then
      let b=$b+1
    fi

    if [ "$b" -lt "1" ]
    then
      let b=1
    elif [ "$b" -ge "$columns" ]
    then
      let b="$columns"
    fi

    echo -ne "\r"

    let c=$(tput cols)
    for i in `seq 1 $c`
    do
      echo -ne " "
    done

    echo -ne "\r"

    for i in `seq 1 $b`
    do
      echo -ne "="
    done
  done
  exit 0
}

main