Bash scripting – CS

#!/bin/bash

• chmod +x <filename>
• to run script: ./<filename>

.bashrc

• customize your bash
• home directory is created from /etc/skel/, this includes default .bashrc and .profile

/etc/skel/.bashrc

• Create/remove alias (b.bashrc)

alias extip='curl icanhazip.com'

unalias

Variables

• in caps
• no spaces near =

HELLO="Hello World"
echo $HELLO

Execution

• df -h
• watch df- h –>every 2s

Numbers

expr

• * is nor for multiplying (* wildcard operator) so use: \*
• let <variable>

tar

• To extract a .tgz file

tar -xvzf /path/to/yourfile.tgz

• To different directory

tar -xvzf /path/to/yourfile.tgz -C /path/where/to/extract/

if

if [ $MYNUM -eq 200 ]
then
else
fi

case

#!/bin/bash

echo "what is favorite color?"
echo "1 - Black"
echo "2 - Red"
echo "3 - White"
echo "4 - Blue"

read color;

case $color in
    1) echo "Night is Black";;
    2) echo "Blood is Red";;
    3) echo "Snow is White";;
    4) echo "Sky is Blue";;
    *) echo "no relevant!";;
esac

while

#!/bin/bash

mika=1

while [ $mika -le 10 ]
do
    echo $mika
    mika=$(( $mika + 1))
    spleep 0.5
done

File/Directory Exists?

• File

if [ -f ~/myfile ]

• Directory

if [ -d ~/myfolder ]

Universal update scripts (<>distros)

#!/bin/bash

cd /etc

## testing arch based
if [ -d /etc/pacman.d ]
then 
    ## Run arch update cmd
    sudo pacman -Syu
fi

## Testing debian-based
if [ -d /etc/apt ]
then 
    ## Run arch update cmd
    sudo apt-get update && sudo apt-get dist-upgrade -y
fi

Standard Input, Output and Error

• stdin (0)
  • read <variable>
• stdout (1)
  • > and >> (append)
• stderror (2)
  • ls /root 2> errors.txt
• /dev/null

File system

• echo $PATH
  • /usr/local/sbin
  • /usr/local/bin
  • /usr/sbin
  • /usr/bin
  • /sbin
  • /bin

File Hierarchy Standard (FHS) recommendation

• for users

/usr/local/bin

• for admins

/usr/local/sbin

• To add path: ~/bin folder edit .bash_profile

PATH=$PATH:$HOME/bin
export PATH

df

df -Th

fdisk

fdisk -l

• mount

mkfs.xfs /dev/xvdf

mount /dev/xvdf /myfoldermount

• to make permanently accessible, add an entry in:

/etc/fstab

/dev/xvdf   /myfoldermount   xfs   defaults   0   0 

mount -a

• check if disk formatted

lbkid

lsblk

du

• list all files and directory size

du -sh * | sort

lsof (list open files)

• count list open files

sudo lsof | wc -l

• for specific user mika

sudo lsof -u mika

ip – ifconfig

/etc/sysconfig/network-scripts/ifcfg-eth0

mlocate

yum install mlocate

updatedb

logged-in users

w

Sending emails

• Need to install packages:

sudo apt-get install sendEmail libio-socket-ssl-perl libnet-ssleay-perl

• Send email

sendEmail -f <fromEmail> -t <toEmail> -u "This is the subject" -m "This is the message" -s smtp.googlemail.com:587 -xu <user> x -xp <password> -o tls=yes

• Send email with disk usage report for sda1

#!/bin/bash

SMTPFROM=jahec2@gmail.com
SMTPTO=jahec2@gmail.com
SMTPSERVER=smtp.googlemail.com:587
SMTPUSER=jahec2
SMTPPASS="<password>"
MESSAGEBODY="This is the message"
SUBJECT="Alert from df -h"

df -h | grep Filesystem > /tmp/diskusage.txt
df -h | grep sda1 >> /tmp/diskusage.txt

sendEmail -f $SMTPFROM -t $SMTPTO -u $SUBJECT -o message-file=/tmp/diskusage.txt -s $SMTPSERVER -xu $SMTPUSER x -xp $SMTPPASS -o tls=yes

rm /tmp/diskusage.txt