Bash: how to simply check disk space on Linux and take action when a threshold is reached

#!/bin/bash
# Ex alert_threshold=90 -> You will be alerted if your occupied space is more or equal than threshold
alert_threshold=90
# Email for alert
rcpt1="nospam@nospam.com"
# Hostname
host=`hostname -f`
i=0
for disk in `df |grep dev |grep -v tmpfs |grep -v udev| awk -F" " '{print $1}' | cut -d/ -f3`
do
        space_use=`df | grep $disk | awk -F" " '{print $5}' | cut -d% -f1`
        if [ "$space_use" -gt "$alert_threshold" ]
        then
                i=$((i + 1))
                over_threshold["$i"]="$disk"
        fi
done
        if [ ${#over_threshold[*]} -gt 0 ]
        then
                echo >/tmp/mail.txt
                subject="Disk space over threshold on $host"
                echo "">> /tmp/mail.txt
                echo "Disks with space problem with more than $alert_threshold% occupied space" >> /tmp/mail.txt
                echo "">> /tmp/mail.txt
                for disk in ${over_threshold[*]}
                        do
                                info_disk=(`df -h | grep $disk | awk -F" " '{print $6, $2, $3, $4, $5}'`)
                                echo "- Mount point : ${info_disk[O]} - Total space : ${info_disk[1]} - Used space : ${info_disk[2]} - Free space : ${info_disk[3]} - Used space in percents : ${info_disk[4]}" >> /tmp/mail.txt ; echo "" >> /tmp/mail.txt
                        done
# Now send the email alert
        cat /tmp/mail.txt |mail -s "$subject" $rcpt1
      fi

wget --no-check-certificate https://www.christophe-casalegno.com/tools/diskcheck.sh ; chmod +x diskcheck.sh