Scripting [In Progress]

Here we will see how to take input from user in a script with the help of read command. #!/bin/bash Lets try multiplication of two numbers which the user enters. What read does is ? It takes values by user on stdin. It prompt the user to input any value on stdin. -p is used to display a prompt. read -p "First number:" value1 This will give a prompt as " First number " and store the value in variable " value1 " echo Will display a blank line. read -p "Second number:" value2 This will give a prompt as " Second number " and store the value in variable " value2 " echo Will display a blank line. read -sn1 -p "Press any key to see the answer..." Just to make it bit more interactive lets add one more thing. -s means silent mode that is if any value is pressed it will not be displayed on the screen like as in the password. -nX means how many characters. X here is one that is any

Here we will see the naming convention of parameters which are passed to a script and how we can use them? how shifting works? #!/bin/bash # Positional parameters #       $0          $1     $2    $3   .......   $n # Command  Arg1 Arg2 Arg3 ....... Argn echo -e "First argument $1, Second argument $2, Third argument $3, Fourth argument $4\n" This will print value of all four arguments which you passed, just for your reference. shift The positional parameters from n+1 ... are renamed  to  $1, so that every time after shift is performed there is a new argument to be processed. This will shift to the left by one value. echo "Shifting...." echo -e "First argument $1, second argument $2, third argument $3, fourth argument $4 \n" This will print new values after shifting the arguments by one value. shift 2 This will shift to the left by two values. echo "Shifting.... by 2 vlaues" echo -e "First argument $1, second

Lets create a file with following content: #!/bin/bash echo "Value which is there in variable USER  is $USER" What this above line will do, it will fetch the variable USER which is built-in. echo -e "-e is used to add new line $USER.\n" Adding -e will execute \n and will add a new line. name=$USER We also can assign the built-in variables to another variables as here value of $USER will be stored in name variable. echo -e "Assigning value of USER variable to another variable $name \n" shortname=$(cat /etc/passwd | grep "sunny" | awk -F ":" '{print $5}' | cut -d " " -f1) Here we are merging various commands. What above line will do is firstly it will cat the file /etc/passwd from that it will grep the line which has sunny. sunny :x:1000:1000:Sunny Bhambhani:/home/sunny:/bin/bash Then by the help of awk command it will get the 5th field which contains the full name of the user. Sunn

Lets create a file with following content: #!/bin/bash echo "$var1" Assign a value to a local variable var1 sunny@sunny-workstation bin]$ var1=sunny-workstation sunny@sunny-workstation bin]$ chmod +x 2_simple_script.sh  When you will run this script it will state nothing. That's because script doesn't know anything about var1 variable and that it exists in shell environment. sunny@sunny-workstation bin]$ ./2_simple_script.sh  sunny@sunny-workstation bin]$ But if we source this script via . or source built-in command it will show the output as the script will run in the same environment as our shell sunny@sunny-workstation bin]$ . ./2_simple_script.sh  sunny-workstation sunny@sunny-workstation bin]$ source 2_simple_script.sh  sunny-workstation sunny@sunny-workstation bin]$

#!/bin/bash First line of the script, lets divide it into pieces: ! is ka she-bang /bin location of bash bash is an interpreter stored in /bin directory. vim is a text editor that supports color coding, that will be really helpful. A good script always have following things: #Author #Date #Contact details #Script usage #Version history Lets try a sample hello world script echo "Hello World"  Print this on stdout echo command is used to print text to your standard output. Add above line in a file called 1_simple_script.sh or any name of your choice. Then we need to change its permission that is we need to get it an execute permission. chmod u+x X.sh If we will not add +x it will show permission denied. There are various ways of executing a script some are given below: [sunny@sunny-workstation bin]$ ~/bin/1_simple_script.sh Hello World [sunny@sunny-workstation bin]$ /home/sunny/bin/1_simple_script.sh Hello World [sunny@sunny-workstation b