$ touch hello.sh // create an empty file
$ atom hello.sh // open atom editor
hello.sh:
--------
#!/usr/bin/env bash
#hello world sample script
echo Hello world!
echo Mars is red!
hadoop@hadoop:~/Desktop/vow/shellscript$ chmod 755 hello.sh
$ ./hello.sh
$ sh hello.sh
Hello world!
Mars is red!
$ touch greeting.sh
$ atom greeting.sh
#!/usr/bin/env bash
FIRST_NAME=Bob
FAVORITE_COLOR=blue
echo Hi $FIRST_NAME, your favorite color is $FAVORITE_COLOR
$ ./greeting.sh
Hi Bob, your favorite color is blue
greeting.sh:
-------------
#!/usr/bin/env bash
FIRST_NAME="Bob Roberts"
FAVORITE_COLOR=blue
echo Hi $FIRST_NAME, your favorite color is $FAVORITE_COLOR
$ ./greeting.sh
Hi Bob Roberts, your favorite color is blue
//Parameters
$0 - name of the script, the path is included
$1, $2, $3, ${10},
${255} - the last parameter
$ touch params.sh
$ atom params.sh
params.sh
------------
#!/usr/bin/env bash
echo File name is, $0
echo First Name : $1
echo Last Name : $2
$ ./params.sh Kapil Dev
File name is, ./params.sh
First Name : Kapil
Last Name : Dev
#!/usr/bin/env bash
FIRST_NAME=$1
LAST_NAME=$2
echo Hello, $FIRST_NAME, $LAST_NAME
echo $`date`
echo $`pwd`
$ bash params.sh sare ga
Hello, sare, ga
$Wed Apr 3 10:15:42 IST 2019
$/home/hadoop/Desktop/vow/shellscript
Challenge:
----------
Create a script named sport.sh
Make it executable
Accept 2 parameters : name and a favorite sport
Display any sentence to the console using those inputs
sport.sh:
----------
#!/usr/bin/env bash
NAME=$1
SPORT=$2
echo $NAME likes to watch $SPORT.
Execute the script:
-------------------
$ sh sport.sh Vijay Soccer
Vijay likes to watch Soccer.
If example:
-----------
#!/usr/bin/env bash
COLOR=$1
if [ $COLOR = "blue" ]
then
echo "The color is blue"
fi
USER_GUESS=$2
COMPUTER=50
if [ $USER_GUESS -lt $COMPUTER ]
then
echo "You are too Low"
fi
$ ./if.sh blue 40
The color is blue
You are too Low
#!/usr/bin/env bash
COLOR=$1
if [ $COLOR = "blue" ]
then
echo "The color is blue"
else
echo "The color is NOT blue"
fi
USER_GUESS=$2
COMPUTER=50
if [ $USER_GUESS -lt $COMPUTER ]
then
echo "You are too Low"
else
echo "You are equal or too high"
fi
$ ./if.sh Orange 55
The color is NOT blue
You are equal or too high
#!/usr/bin/env bash
USER_GUESS=$1
COMPUTER=50
if [ $USER_GUESS -lt $COMPUTER ]
then
echo "You are too low"
elif [ $USER_GUESS -gt $COMPUTER ]
then
echo "You are too High"
else
echo "You have guessed it"
fi
$ ./if.sh 50
You have guessed it
$ ./if.sh 44
You are too low
$ ./if.sh 66
You are too High
whileexa.sh:
------------
#!/usr/bin/env bash
COUNT=0
while [ $COUNT -lt 10 ]
do
echo "COUNT = $COUNT"
((COUNT++))
done
echo "While Loop Finished!".
exit 0
$ ./whileexa.sh
COUNT = 0
COUNT = 1
COUNT = 2
COUNT = 3
COUNT = 4
COUNT = 5
COUNT = 6
COUNT = 7
COUNT = 8
COUNT = 9
While Loop Finished!.
for.sh: (for each - multiple arguments)
-------
#!/usr/bin/env bash
NAMES=$@
for NAME in $NAMES
do
echo "Hello $NAME"
done
echo "for loop terminated"
$ ./for.sh a b c d e f g h (n number of variable number of arguments)
Hello a
Hello b
Hello c
Hello d
Hello e
Hello f
Hello g
Hello h
for loop terminated
$ ./for.sh Awesome Outstanding Tremendous
Hello Awesome
Hello Outstanding
Hello Tremendous
for loop terminated
// break example
for.sh:
-------
#!/usr/bin/env bash
NAMES=$@
for NAME in $NAMES
do
if [ $NAME = "Tracy" ]
then
break
fi
echo "Hello $NAME"
done
echo "for loop terminated"
$ ./for.sh Stacy Tracy Lacy
Hello Stacy
for loop terminated
Challenge:
-----------
Write a script named counter.sh
It should count from 1 to the number entered by the user
Through the loop, display the current count value
Once the loop terminates, display "Loop finished"
#!/usr/bin/env bash
COUNT=1
END=$1
while [ $COUNT -le $END ]
do
echo "COUNT = $COUNT"
((COUNT++))
done
echo "Loop Finished."
$ ./counter.sh 5
COUNT = 1
COUNT = 2
COUNT = 3
COUNT = 4
COUNT = 5
Loop Finished.
$ ./counter.sh 7
COUNT = 1
COUNT = 2
COUNT = 3
COUNT = 4
COUNT = 5
COUNT = 6
COUNT = 7
Loop Finished.
//Environment variable example
vars.sh:
--------
#!/usr/bin/env bash
echo "The PATH is : $PATH"
echo "The terminal is : $TERM"
echo "The editor is : $EDITOR"
if [ -z $EDITOR ]
then
echo "The EDITOR variable is not set"
fi
PATH="/bob"
echo "The PATH IS : $PATH"
output:
---------
$ ./vars.sh
The PATH is : /usr/local/hive/bin:/usr/local/hive/lib:/usr/local/spark/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/usr/local/java/bin:/usr/local/hadoop/bin:/usr/local/hadoop/sbin:/usr/local/kafka/bin
The terminal is : xterm-256color
The editor is :
The EDITOR variable is not set
The PATH IS : /bob
HOME - user's home directory
PATH - directories which are searched for commands
HOSTNAME - hostname of the machine
SHELL - shell thats being used
USER - user of this session
TERM - type of command-line terminal that is being used
// display environmental variables
$ echo $HOME
/home/hadoop
$ echo $PATH
/usr/local/hive/bin:/usr/local/hive/lib:/usr/local/spark/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/usr/local/java/bin:/usr/local/hadoop/bin:/usr/local/hadoop/sbin:/usr/local/kafka/bin
$ echo $HOSTNAME
hadoop
$ echo $SHELL
/bin/bash
$ echo $TERM
xterm-256color
$ echo $USER
hadoop
Challenge:
----------
Create a Script named : env.sh
Display a sentence
Include the computer name, user's name, home directory
env.sh:
--------
#!/usr/bin/env bash
echo "The computer's name is $HOSTNAME, the user's name is $USER, AND THE home directory is $HOME"
exit 0
$ ./env.sh
The computer's name is hadoop, the user's name is hadoop, AND THE home directory is /home/hadoop
Function Example:
-------------------
#!/usr/bin/env bash
function Hello(){
echo "Hello!"
}
Goodbye(){
echo "Goodbye!"
}
echo "Calling the Hello function"
Hello
echo "Calling the Goodbye function"
Goodbye
# Do not call like Goodbye()
exit 0
#define the function first, then call it later
$ ./func.sh
Calling the Hello function
Hello!
Calling the Goodbye function
Goodbye!
// Function with Parameters example
#!/usr/bin/env bash
function Hello(){
local LNAME=$1
echo "Hello! $LNAME"
}
Goodbye(){
echo "Goodbye! $1"
}
echo "Calling the Hello function"
Hello Steve
echo "Calling the Goodbye function"
Goodbye David
exit 0
$ ./func.sh
Calling the Hello function
Hello! Steve
Calling the Goodbye function
Goodbye! David
//pipe operation example:
#!/usr/bin/env bash
FILES=`ls -1 | sort -r | head -3`
COUNT=1
for FILE in $FILES
do
echo "FILE #$COUNT : $FILE"
((count++))
done
exit 0
output:
----------
$ ./pipe.sh
FILE #COUNT : whileexa.sh
FILE #COUNT : vars.sh
FILE #COUNT : sport.sh
Challenge:
----------
Create a script named pfunc.sh
Create two functions in the script:
a) GetFiles,
b) ShowFiles
GetFiles returns the first 10 files in the directory
pfunch.sh:
-----------
#!/usr/bin/env bash
function GetFiles(){
FILES=`ls -1 | sort | head -10`
}
function ShowFiles(){
local COUNT=1
for FILE in $@
do
echo "FILE #$COUNT : $FILE"
((COUNT++))
done
}
GetFiles
ShowFiles $FILES
exit 0
output:
-------
$ ./pfunch.sh
FILE #1 : counter.sh
FILE #2 : env.sh
FILE #3 : for.sh
FILE #4 : func.sh
FILE #5 : greeting.sh
FILE #6 : hello.sh
FILE #7 : if.sh
FILE #8 : params.sh
FILE #9 : pfunch.sh
FILE #10 : pipe.sh
File Example:
--------------
names.txt:
----------
Ravi
Kumar
Aradhana
Siva
Karthikeyan
Dhanush
Viswanathan
SelvaKumar
Ulagappan
fileReader.sh:
---------------
#!/usr/bin/env bash
COUNT=1
while IFS="" read -r LINE
do
echo "LINE $COUNT : $LINE"
((COUNT++))
done < "$1"
exit 0
//IFS means Internal Field Separator \t \n ,
// execute the script and pass names.txt as input argument / parameter
$ ./fileReader.sh names.txt
LINE 1 : Ravi
LINE 2 : Kumar
LINE 3 : Aradhana
LINE 4 : Siva
LINE 5 : Karthikeyan
LINE 6 : Dhanush
LINE 7 : Viswanathan
LINE 8 : SelvaKumar
LINE 9 : Ulagappan
// create a file using redirection operators
$ ./fileReader.sh names.txt > output1.txt // overwrite / create
$ ./fileReader.sh names.txt >> output1.txt // append
$ cat output1.txt
LINE 1 : Ravi
LINE 2 : Kumar
LINE 3 : Aradhana
LINE 4 : Siva
LINE 5 : Karthikeyan
LINE 6 : Dhanush
LINE 7 : Viswanathan
LINE 8 : SelvaKumar
LINE 9 : Ulagappan
LINE 1 : Ravi
LINE 2 : Kumar
LINE 3 : Aradhana
LINE 4 : Siva
LINE 5 : Karthikeyan
LINE 6 : Dhanush
LINE 7 : Viswanathan
LINE 8 : SelvaKumar
LINE 9 : Ulagappan
// cksum of a file
//whether the file is tampered or not
hadoop@hadoop:~/Desktop/vow/shellscript$ cat names.txt
Ravi
Kumar
Aradhana
Siva
Karthikeyan
Dhanush
Viswanathan
SelvaKumar
Ulagappan
hadoop@hadoop:~/Desktop/vow/shellscript$ cksum names.txt // original
4016456064 78 names.txt // 3 parameters checksum value, filesize,filename
hadoop@hadoop:~/Desktop/vow/shellscript$ atom names.txt
Ravi
Kumar
Aradhana
Siva
Karthikeyan
Dhanush
Viswanaathan // added one extra 'a'
SelvaKumar
Ulagappan
hadoop@hadoop:~/Desktop/vow/shellscript$ cksum names.txt
783674190 79 names.txt // because of file tampered, the cksum value changed
hadoop@hadoop:~/Desktop/vow/shellscript$ atom names.txt
Ravi
Kumar
Aradhana
Siva
Karthikeyan
Dhanush
Viswanathan // removed extra 'a'
SelvaKumar
Ulagappan
hadoop@hadoop:~/Desktop/vow/shellscript$ cksum names.txt
4016456064 78 names.txt // file is not tampered - i mean transported without any corruption, or modification
4016456064 -- value should be sent via e-mail. that number should match before and after tranfer
Challenge:
----------
Create a script named read3.sh
Have it read a file name passed as a parameter
It should only display the first 3 lines, with count
read3.sh:
--------
#!/usr/bin/env bash
COUNT=1
while IFS="" read -r LINE
do
echo "LINE $COUNT : $LINE"
if [ $COUNT -ge 3 ]
then
break
fi
((COUNT++))
done < "$1"
exit 0
output:
--------
$ ./read3.sh names.txt
LINE 1 : Ravi
LINE 2 : Kumar
LINE 3 : Aradhana
delayexa.sh:
-------------
#!/usr/bin/env bash
DELAY=$1
if [ -z $DELAY ]
then
echo "You must supply a delay"
exit 1
fi
echo "Going to sleep for $DELAY seconds"
sleep $DELAY
echo "We are awake now."
exit 0
// put & at the end.
$ ./delayexa.sh 5 &
[1] 5833 // process id of the script running in background
hadoop@hadoop:~/Desktop/vow/shellscript$ Going to sleep for 5 seconds
We are awake now.
[1]+ Done ./delayexa.sh 5
output:
-------
$ ./delayexa.sh 5
Going to sleep for 5 seconds
We are awake now.
proc.sh:
---------
#!/usr/bin/env bash
STATUS=0
if [ -z $1 ]
then
echo "Please supply a PID"
exit 1
fi
echo "Watching PID = $1"
while [ $STATUS -eq 0 ]
do
ps $1 > /dev/null
STATUS=$?
done
echo "Process $1 has terminated"
exit 0
// open a new terminal window, and start nano editor
$ nano a
$ ps -a
PID TTY TIME CMD
5971 pts/1 00:00:00 nano // see the process id for nano is 5971
5973 pts/0 00:00:00 ps
// start the shell script
$ ./proc.sh 5971
Watching PID = 5971
// stop nano
Process 5971 has terminated
// run the delayexa.sh script
$ ./delayexa.sh 20 &
[1] 8468
hadoop@hadoop:~/Desktop/vow/shellscript$ Going to sleep for 20 seconds
We are awake now.
// pass the process id of delay program
$ ./proc.sh 8468
Watching PID = 8468
Process 8468 has terminated
//Get input from user
prompt.sh:
----------
#!/usr/bin/env bash
read -p "What is your first name? " NAME
echo "Your name is : $NAME"
exit 0
output:
-------
$ ./prompt.sh
What is your first name? sarega
Your name is : sarega
//validating user input in shell scripting:
user.sh:
---------
#!/usr/bin/env bash
VALID=0
while [ $VALID -eq 0 ]
do
read -p "Please enter your name and age : " NAME AGE
if [[ ( -z $NAME ) || ( -z $AGE ) ]]
then
echo "Not enough parameters passed"
continue
elif [[ ! $NAME =~ ^[A-Za-z]+$ ]]
then
echo "Non Alpha characters detected [ $NAME ]"
continue
elif [[ ! $AGE =~ ^[0-9]+$ ]]
then
echo "Non digit characters detected [ $AGE ]"
continue
fi
VALID=1
done
echo "Name = $NAME and Age = $AGE"
exit 0
output:
---------
$ ./user.sh
Please enter your name and age : SARA 40
Name = SARA and Age = 40
hadoop@hadoop:~/Desktop/vow/shellscript$ ./user.sh
Please enter your name and age :
Not enough parameters passed
Please enter your name and age : SA
Not enough parameters passed
Please enter your name and age : SA 3
Name = SA and Age = 3
//Challenge
Create a script named guess.sh
Set a global variable named COMPUTER to a number between 1 and 50
Take input from the user
if the user's input matches COMPUTER, they won
guess.sh:
---------
#!/usr/bin/env bash
COMPUTER=50
PLAYING=0
while [ $PLAYING -eq 0 ]
do
read -p "What's your guess : " INPUT
if [ $INPUT -eq $COMPUTER ]
then
echo "You've won, the number was $COMPUTER"
exit 0
elif [ $INPUT -lt $COMPUTER ]
then
echo "You're too low"
fi
done
exit 0
$ ./guess.sh
What's your guess : 3
You're too low
What's your guess : 5
You're too low
What's your guess : 50
You've won, the number was 50
