Uly.me

cloud engineer

bash

AWS Create Volume From Snapshot

Here’s a bash script that creates a volume from a snapshot in AWS.

#!/bin/bash
read -p "snapshotId : " snapshot
read -p "server     : " server
read -p "tag1       : " tag1
read -p "tag2       : " tag2
read -p "region     : " region
read -p "zone       : " zone
read -p "profile    : " profile
aws ec2 create-volume \
--availability-zone $zone \
--encrypted \
--iops 3000 \
--volume-type gp3 \
--snapshot-id $snapshot \
--tag-specifications "ResourceType=volume,Tags=[{Key=Name,Value="$server"},{Key=tag1,Value="$tag1"},{Key=tag2,Value="$tag2"}]" \
--region $region \
--profile $profile

Open Browser in Bash

Here’s a nice little command to open a browser from Bash.

#!/bin/bash
open https://domain.com/path/to/web/page/index.html

You can use this command to open a web page from your script.

Bash Any Key

Here’s the script to add pauses in your Bash script.

echo "please wait until web page loads ... "
read -p "Press any key to continue... " -n1 -s

You can also put it inside a function and call it multiple times.

function press_any_key {
  echo "please wait until web page loads ... "
  read -p "Press any key to continue... " -n1 -s
}
press_any_key

Crop Factor Calculator

If you’re into photography, you would know what crop factor means. I have a Nikon D90 camera with a crop factor of 1.5. For example, if you use a 24mm full frame lens on a D90, the focal length will be 36mm. So, here’s a handy bash script that calculates the crop factor by multiplying the full frame focal length by 1.5.

#!/bin/bash
if [ $# -eq 0 ]
  then
    echo "Usage: cropfactor.sh 24"
    exit
fi
a=$(echo "1.5 * $1" | bc)
echo "Cropfactor focal length is: " $a"mm."

Result

ulysses@penguin:~/Code$ ./cropfactor.sh 24
Cropfactor focal length is:  36.0mm.

Bash Menu and Functions

How to integrate menus and functions in your Bash script.

#!/bin/bash
function show_logs {
ls -l /var/log/
}
function show_users {
cat /etc/passwd
}
echo '--------'
echo 'My Menu'
echo '--------'
PS3='Choose an option: '
commands=("Show logs" "Show users" "Quit")
COLUMNS=0
select cmd in "${commands[@]}"; do
    case $cmd in
        "Show logs")
            echo "Showing logs ... "
            show_logs
            ;;
        "Show users")
            echo "Showing users ... "
            show_users
            ;;
	"Quit")
	    echo "Exiting ... "
	    exit
	    ;;
        *) echo "invalid option $REPLY";;
    esac
done

Result

--------
My Menu
--------
1) Show logs
2) Show users
3) Quit

Cleanup Stale CVS Snapshots

Here’s the script that looks mounts with stale file handles and removes them.

#!/bin/bash
file='/tmp/stale.txt'
df -h | grep Stale > $file
sed -i -e 's/df: ‘/'""'/g' $file
sed -i -e 's/’: Stale file handle/'""'/g' $file
while IFS= read -r line; do
  echo 'unmounting '$line
  umount $line
done < $file

Cleanup CVS Snapshot Volumes

How to unmount CVS snapshot volumes all at once using a Bash script. I ran into a scenario where I had to unmount 115 volumes. Instead of manually running umount on each one, I use the script below to unmount all 115 volumes. The script performs a grep for ‘.snapshot’ and then writes the results to a file. I then read the file line by line and perform unmount on each one.

#!/bin/bash
file='/tmp/snapshots.txt'
df -h | grep .snapshot | awk '{print $6}' > $file
while IFS= read -r line; do
  echo 'unmounting '$line
  umount $line
done < $file

Bash Spacebar Break

Here’s how to add breaks in your Bash scripts. The function is called spacebar.

function spacebar {
  echo 'Press spacebar to continue. Press Ctrl-C to exit.'
  stty -echo > /dev/null
  until read -r -n 1 -t 0.001 && [ "$REPLY" = ' ' ]; do abc=''; done
  stty echo > /dev/null
}
 
spacebar

You can call it multiple times in your script since it’s a function.