Bash

Basics

Source: ss64.com

This section is under construction.

• Echo continue on same line:

echo -n "Count: " >> files.txt
find . | wc -l >> files.txt

• Variable

$1, $2, $3    are the positional parameters.
"$@"          is an array-like construct of all positional parameters, {$1, $2, $3 ...}.
"$*"          is the IFS expansion of all positional parameters, $1 $2 $3 ....
$#            is the number of positional parameters.
$-            current options set for the shell.
$$            pid of the current shell (not subshell).
$_            most recent parameter (or the abs path of the command to start the current shell immediately after startup).
$IFS          is the (input) field separator.
$?            is the most recent foreground pipeline exit status.
$!            is the PID of the most recent background command.
$0            is the name of the shell or shell script.

• Using Variables in Bash:

dir="/data/.folder/"
path="/home/system/Desktop/pending_files.txt"
tree $dir | wc -l >> $path

Bash Scripts

One Liners

• Script to find file extensions

find $dir -type f | perl -ne 'print $1 if m/\.([^.\/]+)$/' | sort -u

• Convert files with name "webp" file to Png:

find . -name "*.webp" -exec dwebp {} -o {}.png \;
find . -name "*.webp" -delete

• Create Multiple Directories with single command:

mkdir ep{1..16}
mkdir -p sa{0..10}/{1,2,3,4}
mkdir -p sa{0..10}/{1..4}

• Download multiple files at once:

wget https://imagedump.com/i/1/234{1..100}.jpg
wget -i list.txt

Medium Scripts

Checking Internet connectivity

#!/bin/bash

if ping -c 1 -W 2 google.com > /dev/null; then
 echo "Up"
else
 echo "Down"
fi

Mplayer Play Live Gurbani from 8 to 10AM

 #!/bin/bash
 trickle -d 20 -u 15 mplayer mms://sgpc.net/live &
 sleep 2h
 kill $!

Cron Entry:

0 8 * * * ./mplayer.sh

Download Newspaper front page

URL:

http://newspaper.ajitjalandhar.com/newspages/20130226/20130226_1_1.jpg

  
 #!/bin/bash
 cd ~/Desktop
 D=$(date +"%Y%m%d")
 FILE="$D"_1_1.jpg
 if [ -f $FILE ];
 then
    exit
 else
    wget "http://newspaper.ajitjalandhar.com/newspages/"$D"/"$D"_1_1.jpg" && notify-send -i /data/Softwares/Wallpapers/icons/ajit.png -t 50 "Ajit Jalandhar" "is saved at your desktop"
 fi

Cron Entry to download daily:

0 7-11 * * * ./ajit.sh

Eye strain preventer

#!/bin/bash
PATH=/usr/games:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

while true; do sleep 1200; sm --foreground=white --background=black Look at an Object 20 feet away for 20 Seconds & sleep 20s && killall sm; done

Add following line to startup programs:

/home/aman/Scripts/eyesaver.sh >/dev/null 2>&1

Extension Doctor

This script will overwrite any existing file.

for f in *.{jpg,JPG,png,PNG,jpeg,JPEG,webp}; do 
    type=$( file "$f" | grep -oP '\w+(?= image)' )
    case $type in  
        PNG)  newext=png ;; 
        JPEG) newext=jpg ;;
        P) newext=webp ;;
        *)    echo "??? what is this: $f"; continue ;; 
    esac
    ext=${f##*.}   # remove everything up to and including the last dot
    if [[ $ext != $newext ]]; then
        # remove "echo" if it's working correctly
        echo mv "$f" "${f%.*}.$newext"
    fi
done

Big Scripts

Directory Stats

#!/bin/bash
#Script to export file/directory stats to a file.

# Path Variables:
dir="/data/"
file="/home/aman/Desktop/pending_files.txt"

# Script starts here:
echo "###########################">> $file

# Date of execution:
date >> $file && echo " ">> $file

# File Stats:
echo -n "No of Files: ">> $file
find $dir -type f | wc -l >> $file && echo " ">> $file

echo -n "No of Directories: ">> $file
find $dir -type d | wc -l >> $file && echo " ">> $file

# Directory size:
echo "Sub directory size: ">> $file
du -h --max-depth=1 $dir | sort -h >> $file && echo " ">> $file

# Huge Files:
echo "100 MB+ Files: ">> $file
find $dir -size +100M -exec ls -sh {} \; | sort -r >> $file && echo " ">> $file

# Image file extension counts:
echo "No of Image Files: ">> $file
echo -n "JPG : " >> $file
find $dir -iname "*.jpg" | wc -l >> $file

echo -n "PNG : " >> $file
find $dir -iname "*.png" | wc -l >> $file

echo -n "GIF : " >> $file
find $dir -iname "*.gif" | wc -l >> $file

echo -n "JPEG: ">> $file
find $dir -iname "*.jpeg" | wc -l >> $file

echo -n "WEBP: ">> $file
find $dir -iname "*.webp" | wc -l >> $file && echo " ">> $file

# Video file extension counts:
echo "No of Video Files: ">> $file
echo -n "WEBM: ">> $file
find $dir -iname "*.webm" | wc -l >> $file

echo -n "MPG : ">> $file
find $dir -iname "*.mpg" | wc -l >> $file

echo -n "3GP : ">> $file
find $dir -iname "*.3gp" | wc -l >> $file

echo -n "DAT : ">> $file
find $dir -iname "*.dat" | wc -l >> $file

echo -n "MP4 : ">> $file
find $dir -iname "*.mp4" | wc -l >> $file

echo -n "AVI : ">> $file
find $dir -iname "*.avi" | wc -l >> $file

echo -n "FLV : ">> $file
find $dir -iname "*.flv" | wc -l >> $file && echo " ">> $file


echo "###########################">> $file
exit

References

• Reference Guide: gnu.org
• Check Scripts for errors: shellcheck.net

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