Shell Scripting

cat /etc/shells ---- to display total shells in our
sleep (sec) ----- to sleep and run
$? --- when code is succesfull it return 0
$1 ---- to get a input in same line
echo ${#variable} ---- to display the string count
set -x ---- to print with an command
set -n ---- to debug the code while running
set -e ---- to stop the while code in

grep{
grep -v "#" ---- to grep the details except
grep -i string ---- to remove the case sencitive
grep -w ---- match exact word
grep -v --- to print execpt that line
grep -o --- to print exact word only
grep -n --- to match the line number
grep -c ---- to match the line count
grep -A "string" 1 --- the string is match
grep -B "string" 2 --- the string is match
grep -C 1 "string" --- before and after print
grep -r "string" * --- to search n a
grep -l "string" --- to print only file names
grep -h "sting" --- to hide the file name
grep -f file filename --- to search from a
grep -E "string|srting|string" --- check with a multiple string
grep "^string" --- to print the starting line with
grep "string$" ---- to printthe match word with the
grep "^$" filename --- to match with an empty
grep "\^" --- print the exact word on it
grep "t...e" --- to match with first and last
grep "\bline\b" --- to print the word and end
grep "yf?" --- the f in the string is
grep "yf*" ---- have f or mor time
grep "[yft]" ---- split with an multiple char
grep "yf+" --- the f in the string is
grep "[a-f]" --- to search with a char to
grep "[a-dp-r]" --- to print with a secquance word
grep "^[xy]" --- to print the line it starting
grep "x{4}" --- check with 4 times
grep "gf{3,4}\b" --- 3 , 4 time only
grep "[[:digit:]] filename --- to print the number where
grep "[[:upper:]] filename --- to print the upper case
grep "[[:lower:]] filename --- to print the lower case
}

jq{
cat filename | jq '.' --- display in a
cat filename | jq -c '.[]' --- display output
}

cut{
cut -f 2 filename ---- to seprate with the
cut -d ':' -f 2,4 filename ---- to filter
cut -d ':' -1,4 filename --output-delimiter=" " ---- to
cut -sf 1 filename ---- to execute with wich

}
awk{
awk ' /version/ { print $4 } ---- to
awk ' NR==1 { print $4 } ---- to
awk -F '[ /]' '/version { print $4 }
awk 'BEGIN { OFS="_" } { print $1,$3 }
awk ' { print NR,$4 } ---- to print
awk ' { print NR,$4,NF } ---- to print
awk ' { print $NF } ---- to print
awk '{ print substr( $1, 3, 1 ) }'
}

tr{
tr '[:upper:]' '[:lower:]' < filename ---- convert upper to
tr 'i' 'I' < filename ---- change the letter
tr -d ',' ---- to delete a command
tr -d '[()]' ---- to delete a multiple command
}

sed {
sed ' ' filename ---- to work like a
sed -n '3p' filename ------- to print exact line
sed -n '3,10p' filename ---- to print in a
sed -n '3,+7p' filename ---- to print a count
sed -n '3~7p' filename ---- to print 3,7,10,13 count
sed '4d' filename ----- to delete 4 line doesn't
sed -i '4,6d' filename ---- to remove the value

}
if [ $num1 -gt $num2 -o $num3 -lt $num4
if [[ $num1 -gt $num2 || $num3 -lt $num4
if (( $num1 > $num2 )) --- use simples

$(whoami) ----- to use the defalt command method
echo $SHELL --- to display the current shell is
ps $$ --- to display the current shell is
ctrl + u ---- to erase the complete line
ctrl + w --- to remove the particular word
type -a (command name) --- to identify the command
#!/bin/bash --- to mention the execute path
chmod +x filename ---- to change the permission of
./filename ---- to execute the file from the terminal
#!/usr/bin/env bash --- to create a env on our
# ---- single line command
<<(mention any word ending with the same name) -----
example
< dkgjkndklgj
dogged
SAMPLE ---- to end it
variables two type
-system
upper case
env
- user-defined
lowercase
var="sai"
echo $var --- to print the output
don't use space to declare the variable
case sensitive
${var}var ---- use { } to decular the variable
echo "hello world $(whoami)" --- to execute the shell
echo 'hello world $HOME' --- doesn't execute the script
\ --- to work like a single qoutes
ls \ && pwd --- to use a multi
unset SAMPLE --- to un set delete variable
read -p "ENTER USER NAME:" (variable) --- to input
(-p) -- prompt
(-t) --- time out input
(-s) --- password input doesn't input
echo $variable ---- to print the user name
echo $(( 1+1 )) --- to use operation +,-
declare -i int=100 ---- to decule a integer data
readony variable ----- used to doesn't change the value
${newvariable?errormessage} ---- to identiye a decular variable
alias --- to set our own command
PS1="TERMINAL" ---- to change our own terminal command
PS1="\u@defined name" ---- to custom our terminal
echo $? --- to check the previes command state
test 10 -gt 5 && echo "10 is greater"
[ 10 -gt 15 ] ---- same like a
((10<15)) --- same like that

if and elif condition
if [ 10 -gt 5 ]
then
echo "10 is greater"
elif [ 10 -gt 20 ]
then
echo "equal"
else
echo "not"
fi

number comparisons
gt --- gather than <
lt---- less than >
ge --- greater or equal to <=
le --- less than or equal to >=
eq ---- equal to =
ne ---- not equal to !=
-a --- and &
-o --- or |

array
x=(1 3 5 "sai")
echo "${x[*]}" ---- print all number

string comparisons
=
!=
-z ---- not null value check

file comparisons
-b
-c
-d ---- to check a directory
-f ---- to check a regular file

cli position
echo $0 --- correct script variable
echo $IFS ---- tab char
cat -stv <<< $IFS --- to display non printable

case statements switch case

case $var in
"sai") echo "in side " ;;
"nmap") "scan tool" ;;
*) echo "no value" ll
esac

loops

for
in
(())
for x in 1 2 3 4 5 6
do
echo $x
done

for (( i=1; i < 10 ; i++ ))
do
for(( j=1 ; j < 10 ; j++ ))
do
echo ${i}${j} || printf "\n"
done
done
-----------
while
while [ expression ]
do
....
done

while :
do
.....
done ----- infinity loop syntex
-------------
--function--

function sai(){
echo good boy;
}
sai;
sai;
------------


my=0
while :
do
read -p "value : " my
if [[ $my -eq 0 ]]
then
echo "running"
else

-----
while get input from another file
while IFS="," read f1 f2 f3 f4
do
echo "$f2"
done < filename
----
input two value and print it
read x;
read y;
echo $((x+y));
echo $((x-y));
echo $((x*y));
echo $((x/y));