README.md

QuickBashScriptHack..^^

This repository contains the quick bash help. The snippets of bash scripts/code help to write the script fast. The snippets will further be added by the time, meanwhile if anyone want to contribute, we will be much happy about it. These are those snippets which I mostly use during writing the scripts.

Command Line Arguments with flags - Approach 1
[Example]~: ./script.sh --domain domain.com --expiry 1996,04,16 --dayslimitwarn 45 --dayslimitcri 30 --detail "my string info"

#!/bin/bash

#Define the arguments list in the start of the file
ARGUMENT_LIST=(
	"domain"
	"expiry"
	"dayslimitcri"
	"dayslimitwarn"
	"detail"
)

#Read arguments
opts=$(getopt \
	--longoptions "$(printf "%s:," "${ARGUMENT_LIST[@]}")" \
	--name "$(basename "$0")" \
	--options "" \
	-- "$@"
)


eval set --$opts

while [[ $# -gt 0 ]]; do
	case "$1" in
					
		--domain)
			DOMAIN=$2
			shift 2
			;;

		--expiry)
			EXPIRY=$2
			shift 2
			;;

		--dayslimitcri)
			DAYLIMITCRI=$2
			shift 2
			;;

		--dayslimitwarn)
			DAYLIMITWARN=$2
			shift 2
			;;
			
		--detail)
			DETAIL=$2
			shift 2
			;;
			
		*)
			break
			;;
	esac
done

#Now you can have the values
echo $DOMAIN
echo $EXPIRY
echo $DAYLIMITCRI
echo $DAYLIMITWARN
echo $DETAIL

If-Statement with multiple condition check or comparison operator

if [[ "$STR1" == "" ]] || [[ "$STR2" == "" ]] || [[ "$STR2" == "" ]];then
	echo "Arguments are not compelete"
	exit  
fi

If-Else-Else_If Statement with multiple condition check or comparison operator

if [[ "$STR1" == "" ]] || [[ "$STR2" == "" ]];then

	echo "Arguments are not compelete"
	exit  

else

	if [[ "$STR1" -gt "$STR2" ]]
	then
		echo "String1: " $STR1 " String2: " $STR2
		exit
	elif [[( "$STR1" -gt "$STR2" )]] && [[( "$STR1" -le "$STR2" )]]
	then
		echo "String1: " $STR1 " String2: " $STR2
		exit 1
	elif [[( "$STR1" -le "$STR2" )]]
	then
		echo "String1: " $STR1 " String2: " $STR2
		exit 2

	fi

fi

If-Statement short notes

#Ref: https://unix.stackexchange.com/questions/109625/shell-scripting-z-and-n-options-with-if
[ -z "$output2" ]  #string is null, that is, has zero length
[ -n "$output" ] #string is not null
[[ "$STR1" == "" ]]
[[ "$1" == "userdel" ]]
[[ "$STR1" -gt "$STR2" ]]
[[( "$STR1" -le "$STR2" )]]
[ ! -d "$dir" ] #dir does not exist
[ "$(echo "$dirperm" | cut -c6)" != "-" ] #Command execution in if statemnet
[ id ] && passing=true #if the command run sucessfull then true the passing flag

Run python command in bash script
You can see that we are substituting or using variable of bash in this command. From python print we have the console output value and then we assign that value to the bash variable for further tasks

DAYS_LEFT=`python -c "from datetime import date; print((date($EXPIRY)-date.today()).days)"`
echo $DAYS_LEFT

Function - Declaration and call a function in bash
I use to define the function in the top of the script and if i have the command lines arguments then I declare the function after it. So we can call the function anywhere in the script

#Function definition
help_function(){

echo "-----HELP FUNCTION-------"
echo "script.sh [OPTIONS BELOW]"

echo "PARAMETERS"
echo ""
echo "--domain <Domain Name>"
echo "--dayslimitcri <Days Limit for Critical>"
echo "--dayslimitwarn <Days Limit for Warning>"
echo "--detail <Other detail>"
echo ""

echo "Info: At this moment all parameters should be present for execution of script"
echo "-------------------------"
}

#Function call
help_function

Loop - Read file line by line

while read line; do
  echo "$line"
done <file.txt

Loop - Simple (Iterate over a list)

for i in element1 element2;
do 

echo $i

done

Get the files/folders from current dir having size in GB - Method 1

du -sh * | awk '($1~/[0-9]+\.?[0-9]*G$/)' | cut -f2 | (while read -r dir_files; do
	find ./$dir_files -prune -exec stat --printf='User: %U | Group: %G | Size: ' {} \; -exec du -sh {} \; 
done)   

Get the files/folders from current dir having size in GB - Method 2

find . -xdev -type f -size +1M -exec stat --printf='User: %U | Group: %G | Size: ' {} \; -exec du -sh {} \;

How to execute a script in execution of any command in linux? like if a user runs "id" command then after that your script would run

#Define/Declare below function in /etc/bashrc 
#~ confirm anycommand
#Ref: https://askubuntu.com/questions/22233/always-prompt-the-user-before-executing-a-command-in-the-shell
#We can show the message on the binaries in this way
confirm() {
    echo -n "Do you want to run $*? [N/y] "
    read -N 1 REPLY
    echo
    if test "$REPLY" = "y" -o "$REPLY" = "Y"; then
		"$@"
	else
        echo "Cancelled by user"
    fi
}

Print message on execution of userdel command in linux and do'nt allow the deletion of user

#Define/Declare below function in /etc/bashrc 
#~ confirm userdel user_name
#We can show the message on the binaries in this way
confirm() {
    echo -n "Do you want to run $*? [N/y] "
    read -N 1 REPLY
    echo
    if test "$REPLY" = "y" -o "$REPLY" = "Y"; then
        if [[ "$1" == "userdel" ]]; then
          echo "Contact to Admin"
        fi
    else
        echo "Cancelled by user"
    fi
}