Bash snippet to emit warning if capacity on disk(s) is ninety percent (90%) or more.

capacitOR.sh

#!/usr/bin/env bash
#
# capacitOR
#
# Emit email if disk capacity is >= 90%.
#
# Author: M. Krinitz <mjk235 [at] nyu [dot] edu>
# Date: 26-JUL-2025
# License: MIT

df="/usr/bin/df"
timestamp="$(date +"%Y-%m-%d %H:%M:%S")"
host="$(hostname -f)"
email_recipients=""
log_file="/var/log/capacitOR.log"
alerts=""

# Set disk capacity threshold, e.g. 90%.
limit=${1:-90}

# Assumed `df` columns are:
# "Filesystem" "1024-blocks" "Used" "Available" "Capacity" "Mounted on"
# If df commaned fails, exit.
if ! df_output="$($df --local --portability -k | grep -v '^Filesystem')"; then
    printf "%s\n" "$timestamp - Error: df parsing failed. Exiting." >> "$log_file"
    exit 1
fi

# Iterate through df_output, checking if capactiy >= limit.
# Accumulate warnings in alerts.
while IFS=" " read -r Filesystem _ _ _ Capacity _ ; do
    capacity="${Capacity%\%}"
    if [[ "$capacity" -ge "$limit" ]]; then
        alerts=$(printf "%s\n" "On $host ${Filesystem} is ${Capacity} full." "$alerts")
    fi
done <<< "$df_output"
 
# If any alerts present, send them via email.
if [[ -n "$alerts" ]]; then
    alerts=$(printf "%s\n" "Please reduce disk capacity on the following drive(s):" \
        "$alerts" "Message sent: $timestamp")

    subject="Disk capacity at $limit% on $host"
    printf "%s\n" "$alerts" | mail -s "$subject" "$email_recipients"

# Log actions.
    printf "%s\n" "$timestamp - Alerts sent for impacted filesystems on $host" >> "$log_file"
else
    printf "%s\n" "$timestamp - No disk capacity alerts triggered on $host" >> "$log_file"
fi