Example of a Bash script that performs the following tasks

1. Checks the availability of an important web server.
2. Checks disk space usage.
3. Makes a backup of the specified directories.
4. Sends a report to the administrator's email.

Example script:

#!/bin/bash

# Settings
WEB_SERVER="https://example.com"
BACKUP_DIR="/backup"
TARGET_DIRS="/var/www /etc"
DISK_USAGE_THRESHOLD=90
ADMIN_EMAIL="admin@example.com"
DATE=$(date +"%Y-%m-%d")
BACKUP_FILE="$BACKUP_DIR/backup-$DATE.tar.gz"

# Checking web server availability
echo "Checking web server availability..."
if curl -s --head $WEB_SERVER | grep "200 OK" > /dev/null; then
echo "Web server is available."
else
echo "Warning: Web server is unavailable!" | mail -s "Problem with web server" $ADMIN_EMAIL
fi

# Checking disk space
echo "Checking disk space..."
DISK_USAGE=$(df / | grep / | awk '{ print $5 }' | sed 's/%//g')
if [ $DISK_USAGE -gt $DISK_USAGE_THRESHOLD ]; then
echo "Warning: Disk space usage exceeded $DISK_USAGE_THRESHOLD%!" | mail -s "Problem with disk space" $ADMIN_EMAIL
else
echo "There is enough disk space."
fi

# Creating backup
echo "Creating backup..."
tar -czf $BACKUP_FILE $TARGET_DIRS

if [ $? -eq 0 ]; then
echo "Backup created successfully: $BACKUP_FILE"
else
echo "Error creating backup!" | mail -s "Error creating backup" $ADMIN_EMAIL
fi

# Sending report
echo "Sending report to $ADMIN_EMAIL..."
REPORT="Report for $DATE\n\n"
REPORT+="Web server status: $(curl -s --head $WEB_SERVER | head -n 1)\n"
REPORT+="Disk space usage: $DISK_USAGE%\n"
REPORT+="Backup location: $BACKUP_FILE\n"

echo -e $REPORT | mail -s "Daily system report" $ADMIN_EMAIL

echo "Done."

Description:

1. Check web server: Uses curl command to check if the site is available.
2. Check disk space: Use df and awk to check disk usage. If the threshold (90%) is exceeded, a notification is sent.
3. Create a backup: The tar command archives and compresses the directories specified in the TARGET_DIRS variable.
4. Send a report: A report on all operations is sent to the administrator's email using mail.

How to use:

1. Set the desired parameters, such as the web server address, directories for backup, disk usage threshold and email.
2. Make the script executable:

chmod +x /path/to/your/script.sh

3. Add the script to cron to run on a regular basis:

crontab -e

Example to run every day at 00:00:

0 0 * * * /path/to/your/script.sh