xxx.php

<?php
    if (rand()%5==0) {
        echo "1111";
    } else {
        echo "0000";
    }
?>

xxx.sh

#/bin/bash

URL="http://192.168.5.100/xxx.php"

check() {
    RESULT=$(curl -s $URL)
    echo $RESULT
    
    if [ "$RESULT" -eq "1111" ] ; then
        echo "again"
        sleep 1
        check
    elif [ "$RESULT" -eq "0000" ] ; then
        echo "exit"
        exit 0
    else 
        echo "error"
    fi
}

check