Bash Scripts.md

Bash Scripts

Anything you can normally run on the command line can also be put into a script for repeated use.

Running Scripts

A user will not have permission to run a saved script by default. We need to grant it first:

chmod a+x script.sh

To run the script:

./script.sh

Scheduling Scripts

To schedule scripts with CRON:

crontab -e

Edit the file to run a script every minute:

* * * * * ~/script.sh

Example Scripts

APT update automation

#!/bin/bash
sudo apt-get udpate &&
sudo apt-get upgrade -y &&
sudo apt-get dist-upgrade -y

Print sum of two inputs

#!/bin/bash
declare -i number1
declare -i number2
declare -i total
echo "Enter a number..."
        read number1
echo "Enter next number..."
        read number2
total=$number1+$number2
echo "The sum of these numbers equals " $total
exit 0

Print index in a loop

#!/bin/bash
for i in {0..10..2}
  do
        echo "We've been through this $i times!"
  done

Print to multiple files

#!/bin/bash
for filename in file1 file2 file3
  do
        echo "Uhn tiss..." >> $filename
  done

If condition is true ... else ...

#!/bin/bash
echo "What is your favorite color? "
read text1
echo "What is your friend's favorite color? "
read text2
        if test $text1 != $text2; then
                echo "I guess opposites attract."
        else
                echo "You two do think alike!"
        fi
exit 0

Print counter while counter is greater than 2

#!/bin/bash
declare -i counter
counter=10
        while [ $counter -gt 2 ];do
                echo "The counter is $counter"
                counter=counter-1
        done
exit 0

Reply to input using a switch case

#!/bin/bash
echo "What's the weather going to be like tomorrow?"
read weather
        case $weather in 
                sunny | warm ) echo "Nice! I love it when it's $weather."
                ;;
                cloudy | cool ) echo "Not bad... $weather is ok."
                ;;
                rainy | cold ) echo "Yuk! $weather weather is depressing."
                ;;
                * ) echo "Sorry, I'm not familiar with that weather system."
                ;;
        esac
exit 0

Print IP

#!/bin/bash

originalAddress=$(   ifconfig | 
                    grep "inet " | 
                    head -n 1 | 
                    tr -s ' ' | 
                    cut -d ' ' -f 3)

echo $originalAddress >> ~/Desktop/ip.txt

Print date and IP in an endless while loop

#!/bin/bash

while [ : ]
do

	originalAddress=$(   ifconfig | 
		            grep "inet " | 
		            head -n 1 | 
		            tr -s ' ' | 
		            cut -d ' ' -f 3)

	echo "$(date) $originalAddress" >> ~/Desktop/ip.txt
	
	sleep 10
done

To watch the output updating every 10s:

tail ip.txt -f