Shell scripting hacks

#  Version : 1.0
#  Author : Nitish Bhardwaj
#  Description : This Script file contains some shell script quick hacks. 


#Check below links to get basics 
#http://linuxconfig.org/linux-commands 
#http://www.thegeekstuff.com/2010/11/50-linux-commands/
#http://www.makeuseof.com/tag/an-a-z-of-linux-40-essential-commands-you-should-know/ 
 
#to check open/closed port on a remote machine
nc -zw3 172.25.1.76 5432 && echo "opened" || echo "closed"
 
#to check ip of devices connected in local network
# http://stackoverflow.com/questions/30644314/list-all-devices-on-local-network
#Method :1
arp -a | grep 192.168.1. | grep ether
#Method :2
for i in `seq 1 254`; do ping -c 1 -q 192.168.1.$i &; done


#to check internet connectivity 
sudo nm-tool | grep "State: connected" | wc -l 
#'1' means connected and '0' means not connnected 
 
#to check ip address 
/sbin/ifconfig eth0 | grep 'inet addr' | cut -d: -f2 | awk '{print $1}' 
 
#to check OS distribution 
lsb_release -i -s 
#http://www.cyberciti.biz/faq/find-linux-distribution-name-version-number/ 
#LSB means (Linux Standard Base) 

#to check OS distribution and version 
lsb_release -d -s 
 
#to copy to remote machine using scp connecting it without RSA key authorization
sshpass -p "$password" scp -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null $algo_script "$username"@"$ip":./
 
#to pass a variable to remote machine using ssh 
sshpass -p "$password" ssh -t "$username"@"$ip" 'export MYVAR='"'$toAlgo'"';sh startHumanTracking.sh' 

#to run a script on remote machine using ssh even after disconnection 
sshpass -p "$password" ssh -x "$username"@"$ip" 'sh startHumanTracking.sh' 
 
#to pass a variable and execute multiple scripts to remote machine using ssh 
sshpass -p "$password" ssh -t "$username"@"$ip" 'export MYVAR='"'$password'"';
sh local_script_2.sh;echo "$password" | sudo -S rm -rf local_script_2.sh package;
echo "$password"|sudo -S sh install_packages_2.sh;echo "$password" | sudo -S rm -rf install_packages_2.sh' 
 
# to split a string based on a delimiter 
#spliting $first based on delimiter '.' and  storing the 4th part to pi_ip 
pi_ip=$(echo $first | awk '{split($0,a,"."); print a[4]}') 
#http://stackoverflow.com/questions/918886/how-do-i-split-a-string-on-a-delimiter-in-bash 
 
#to run installation and output to terminal as well as write to log file 
sudo apt-get install $some_package  | tee -a writer.log 
 
#to run installation/any command and silent the console messages or warning
sudo apt-get install $some_package 2>/dev/null

#to check python package $1 with version $2  
temp=`python -c "import "$1"; print "$1".__version__== '$2'"`  
    
#Grep (an acronym for “Global Regular Expression Print”) 
#to find and replace some string in all the files in a folder 
 grep -rl "old_string" /home/path/*.files |  xargs sed -i "s/old_string/new_string/g" 
 
#to find some string along with the context 
 grep -r "some_string" /home/path/folder 
 
#to extract files from ISO image 
sudo mount -o loop <image>.iso /mnt/iso 

#to show byte information of an ISO and truncate ISO size
#http://softwarebakery.com/shrinking-images-on-linux
sudo fdisk -l <image>.iso
sudo truncate --size=$[(31116287+1)*512] <image>.iso
#'31116287' is the last filled bit in the disk; check from the results of fdisk

#to check storage devices
df -h 

#Taking ISO image of SD card 
sudo dd if=/dev/mmcblk0 of=/home/nitish/Desktop/jasper_complete.iso 

#Burning SD card with ISO files 
sudo dd if=/home/nitish/Desktop/pi_iso/latest_228.iso of=/dev/mmcblk0 

#Expanding the SD Card 
 sudo raspi-config

#to extract a running process and kill the process 
kill -9 $(ps -ef | grep 'processX' | grep -v grep | awk 'NR==1' | awk '{split($0,a," "); print a[2]}') 
kill -9 `ps aux|grep mjpg_streamer|awk '$17== "HumanTracking.jpg" {print $2}'`

#to extract multiple instances of a running process and kill the processes
while [ $(ps -ef | grep 'redis-server' | grep -v grep | wc -l) -ge 1 ]
 do
    echo $password | sudo -S  kill -9 $(ps -ef | grep 'redis-server' | grep -v grep | awk 'NR==1' |  awk '{split($0,a," "); print a[2]}')
 done

#to read from a file line by line separated by Internal Field Separator ':' 
while IFS=: read -r f1 f2 
do 
echo f1 + f2 
done < $config_file  

#to launch GUI firefox from remote machine
sshpass -p "$password" ssh -X "$username"@"$ip" 'export DISPLAY=":0";firefox "www.google.com"'

#to empty a file without deleting the file
cat /dev/null > temp.txt


sed -i '1icolumn1, column2, column3' testfile.csv
#The "1i" command tells sed to go to line 1 and insert the text there.
#The -i option causes the file to be edited "in place" 
#and can also take an optional argument to create a backup file, for example

sed -i~ '1icolumn1, column2, column3' testfile.csv
#would keep the original file in "testfile.csv~".

#http://unix.stackexchange.com/questions/40786/how-to-do-integer-float-calculations-in-bash-or-other-languages-frameworks

#If you want to delete lines 5 through 10 and 12:
sed -e '5,10d;12d' file
#This will print the results to the screen. If you want to save the results to the same file:
sed -i.bak -e '5,10d;12d' file
#This will back the file up to file, and delete the given lines.

sed -n '4p' file
#it will return the text at line number 4

#to kill an open port, say 3000
sudo kill -9 $(sudo lsof -t -i:3000)


#to set up a cron job
#http://www.makeuseof.com/tag/5-beginner-linux-setup-ideas-cron-jobs-shell-scripts/

#to check all the installed packages
dpkg -l 


#to find number of characters in a variable
x="This is a test. S"
grep -o "[s|S]" <<<"$x" | wc -l
#output : 4


#to split and combine a big size file
#Lets says I have an image and its too big (10MB). All I do is:
split --bytes=1M /path/to/image/image.jpg /path/to/image/prefixForNewImagePieces
#and then to put it together I use cat:
cat prefixFiles* > newimage.jpg


#Arithmetic in bash is done with $ and double parentheses:
echo "$(($num1+$num2))"
#Or $ and square brackets:
echo "$[$num1+$num2]"
#You can assign from that (sans echo). There is also expr:
echo `expr "$num1" + "$num2"`

#scale=4 tells bc to use four decimal places
echo 'scale=4;3.1415+9.99' | bc

#https://www.digitalocean.com/community/tutorials/how-to-use-find-and-locate-to-search-for-files-on-a-linux-vps
#Using the find command to recursively delete temp files
find -name *~ -exec rm -rf {} \;


#to check video length
for i in $(pwd)/*; do echo $i; ffmpeg -i $i 2>&1 | grep Duration | cut -d ' ' -f 4 | sed s/,//; done


#to check for images files from terminal and do some ops
for i in "$(pwd)"/*.jpg; do grep -n $(basename $i) ../training-labels | cut -d ':' -f 2| tee -a tagging.log; done;

#to resize image
find training-images/ -name "*.jpg" -exec convert {} -resize 128x128! {} \;

#one liner script for a scheduler
 while true; do mintime=$(date +"%M"); secondtime=$(date +"%S");if [ "$mintime" -eq "48" ] && [ "$secondtime" -eq "50" ];then echo $(date); break; else echo "hi"; fi; done;