Linux implements the source code of the number guessing game

#!/bin/bash
clear
echo
echo "# ...
echo "# this is a bash-shell game written by lee #"
echo "# this game is infinite frequency guess the number#"
echo "# version 2.1.1.20200421 #"
echo "# ...
echo -e "\n\n"
declare INPUT
declare PASSWORD
declare LEN_PWD
declare A
declare B
declare LOOP

#this function is to create a random number
random_number()
{
 PASSWORD=$RANDOM
 LEN_PWD=`echo $PASSWORD | wc -L`
 if [[ $LEN_PWD -ne 4 ]]
 then
 random_number
 else
 #Output standard value, required for testing, comment out echo $PASSWORD after development
 input
 fi
}

#this function is to accept the input from the user's keyboard
input()
{
 read -n4 -p "please input a number between 0000-9999:" input
# 10#${input} base conversionif [[ 10#${input} -eq 10#${PASSWORD} ]]
 then
 echo -e "\n"
 echo "###################################################"
 echo "#congratulations!You have tried $LOOP times!#"
 echo "# The password is $PASSWORD ! #"
 echo "###################################################"
 exit
 elif [[ $LOOP -eq 6 ]]
 then
 echo -e "\n"
 echo "You have tried $LOOP times!Game over!"
 exit
 else
 A=0
 B=0
 count_a
 count_b
 echo -e "\n"
 echo "********************************"
  echo "* "$A"A"$B"B *"
  echo "********************************"
 echo "You have tried $LOOP times! You left `expr 6 - $LOOP` times!"
 LOOP=`expr $LOOP + 1`
 input
 fi
}

#this function is count the variable A's value
count_a()
{
 for i in `seq 4`
 do
 VAR_INPUT=`expr substr $input $i 1`
 for j in `seq 4`
 do
 VAR_PASSWORD=`expr substr $PASSWORD $j 1`
 if [[ $VAR_INPUT -eq $VAR_PASSWORD ]] && [[ $i -eq $j ]]
 then A=`expr $A + 1`
 fi
 done
 done
}

#this function is count the variable B's value
count_b()
{
 for i in `seq 4`
 do
 VAR_INPUT=`expr substr $input $i 1`
 for j in `seq 4`
 do
 VAR_PASSWORD=`expr substr $PASSWORD $j 1`
 if [[ $VAR_INPUT -eq $VAR_PASSWORD ]] && [[ $i -ne $j ]]
 then B=`expr $B + 1`
 fi
 done
 done
}

LOOP=1
random_number