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diff --git a/ult/ult_8/script.rst b/ult/ult_8/script.rst new file mode 100644 index 0000000..1e3f425 --- /dev/null +++ b/ult/ult_8/script.rst @@ -0,0 +1,348 @@ +.. Objectives +.. ---------- + + .. At the end of this tutorial, you will be able to: + + .. 1. Prepare a simple shell script. + .. 2. Run a script successfully and print it's result. + .. 3. Understand what an environment variable is. + +.. Prerequisites +.. ------------- + +.. 1. Getting started with Linux +.. 2. Basic file handling +.. 3. Redirection and Piping +.. 4. Text Processing + + + +Script +------ + +.. L1 + +{{{ Show the first slide containing title, name of the production +team along with the logo of MHRD }}} + +.. R1 + +Hello friends and Welcome to the tutorial on +'Shell scripts & Variables'. + +.. L2 + +{{{ Show slide with objectives }}} + +.. R2 + +At the end of this tutorial, you will be able to, + + 1. Prepare a simple shell script. + #. Run a script successfully and print it's result. + #. Understand what an environment variable is. + +.. L3 + +{{{ Switch to the pre-requisite slide }}} + +.. R3 + +Before beginning this tutorial,we would suggest you to complete the +previous tutorials as being displayed currently. + +.. R4 + +Let us start with creating a simple shell script. +A shell script is simply a sequence of commands, that are put into a file, +instead of entering them one by one onto the shell. The script can then be +run, to run the sequence of commands in a single shot instead of manually +running, each of the individual commands. +For instance, let's say we wish to create a directory called ``marks`` in the +home folder and save the results of the students into a file +``results.txt``. + +.. L4 + +.. R5 + +We open an editor and save the following text to ``results.sh`` + +.. L5 + +{{{ Open an editor and type the following }}} +:: + + #!/bin/bash + mkdir ~/marks + cut -d " " -f 2- marks1.txt | paste -d " " students.txt - | sort > ~/marks/ + results.txt + +.. R6 + +We can now run the script as, + +.. L6 + +{{{ Open the terminal }}} +:: + + ./results.sh + +.. R7 + +We get an error saying, Permission denied! Why? Can you think of the +reason? Yes, the file doesn't have execute permissions. +We make the file executable and then run it. + +.. L7 +:: + + chmod u+x results.sh + ./results.sh + +.. R8 + +We get back the prompt. We can check the contents of the file +``results.txt`` to see if the script has run. + +So, here, we have our first shell script. The first line of the script is used +to specify the interpreter or shell which should be used to execute the script. +In this case, we are asking it to use the bash shell. +Once, the script has run, we get back the prompt. Here, we had to manually +check, if the contents of the file are correct. It would be useful to have our +script print out messages. For this, we can use the ``echo`` command. We can +edit ``results.sh`` script, as follows. + +.. L8 + +{{{ Open an editor and type the following }}} +:: + + #!/bin/bash + mkdir ~/marks + cut -d " " -f 2- marks1.txt | paste -d " " students.txt - | sort > ~/marks/ + results.txt + echo "Results generated." + +.. R9 + +Now, on running the script, we get a message on the screen informing us, +when the script has run. + +Let's now say, that we wish to let the user decide the file to which the +results should be written to. The results file, should be specifiable by an +argument in the command line. We can do so, by editing the file, as below. + +.. L9 + +{{{ Make the necessary changes in the previous script }}} + +:: + + #!/bin/bash + mkdir ~/marks + cut -d " " -f 2- marks1.txt|paste -d " " students.txt - | sort > ~/marks/$1 + echo "Results generated." + + +{{{ Highlight the text ``$1`` }}} + +.. R10 + +The ``$1`` above, corresponds to the first command line argument to the +script. So, we can run the script as shown below, to save the results to +``grades.txt``. + +.. L10 +:: + + ./results.sh grades.txt + +.. R11 + +When we run the ``results.sh`` file, we are specifying the location of the +script by using ``./``. But for any of the other commands, +we didn't have to specify their locations. Why? The +shell has a set of locations where it searches, for the command that we are +trying to run. + +.. L11 + +.. L12 + +{{{ Show slide, PATH }}} + +.. R12 + +These set of locations are saved in an "environment" +variable called PATH.let us look at what the value of the PATH variable is. +To view the values of variables, we can use the echo command. + +.. L13 + +{{{ Switch to the terminal }}} +:: + + echo $PATH + +.. R13 + +So, these are all the paths that are searched, when looking to execute a +command. If we put ``results.sh`` script in one of these locations, we +could simply run it, without using the ``./`` at the beginning. + +.. R14 + +As expected, it is possible to define our own variables inside our shell +scripts. For example, + +.. L14 + +{{{ Switch to the terminal }}} +:: + + name="FOSSEE" + +.. R15 + +It creates a new variable ``name`` whose value is ``FOSSEE``. To refer to this +variable, inside our shell script, we would refer to it, as ``$name``. +Note that, there is no space around the ``=`` sign. + +.. L15 +:: + + ls $name* + + +.. R16 + +It is possible to store the output of a command in a variable, by enclosing +the command in back-quotes. + +.. L16 +:: + + count=`wc -l wonderland.txt` + +.. R17 + +It saves the number of lines in the file ``wonderland.txt`` in the variable +count. + +.. L17 + +.. L18 + +{{{ Show slide, variables & comments }}} + +.. R18 + +The ``#`` character is used to comment out content from a shell script. +Anything that appears after the ``#`` character in a line, is ignored by +the bash shell. + +.. L19 + +{{{ Switch to 'Summary' slide }}} + +.. R19 + +This brings us to the end of the end of this tutorial. +In this tutorial, we have learnt to, + +1. Prepare a shell script. +#. Display the result of a script, using the ``echo`` command. +#. Use the environment variable ``PATH``. +#. Create variables and comment out content using the ``#`` sign. + +.. L20 + +{{{ Show self assessment questions slide }}} + +.. R20 + +Here are some self assessment questions for you to solve + +1. Which sign is used to comment out content from a shell script. + + - $ + - % + - # + - * + +2. How will you add directory ``/data/myscripts`` to the beginning of + the $PATH environment variable ? + +.. L21 + +{{{ Solution of self assessment questions on slide }}} + +.. R21 + +And the answers, + +1. We use the ``#`` sign to comment out the content from a shell script. + +2. In order to add a directory to the beginning of the $PATH variable,we + say, +:: + + $PATH=/data/myscripts:$PATH + +.. L22 + +{{{ Show the SDES & FOSSEE slide }}} + +.. R22 + +Software Development techniques for Engineers and Scientists - SDES, is an +initiative by FOSSEE. For more information, please visit the given link. + +Free and Open-source Software for Science and Engineering Education - FOSSEE, is +based at IIT Bombay which is funded by MHRD as part of National Mission on +Education through ICT. + +.. L23 + +{{{ Show the ``About the Spoken Tutorial Project'' slide }}} + +.. R23 + +Watch the video available at the following link. It summarises the Spoken +Tutorial project.If you do not have good bandwidth, you can download and +watch it. + +.. L24 + +{{{ Show the `` Spoken Tutorial Workshops'' slide }}} + +.. R24 + +The Spoken Tutorial Project Team conducts workshops using spoken tutorials, +gives certificates to those who pass an online test. + +For more details, contact contact@spoken-tutorial.org + +.. L35 + +{{{ Show the ``Acknowledgements'' slide }}} + +.. R35 + +Spoken Tutorial Project is a part of the "Talk to a Teacher" project. +It is supported by the National Mission on Education through ICT, MHRD, +Government of India. More information on this mission is available at the +given link. + +.. L26 + +{{{ Show the Thank you slide }}} + +.. R26 + +Hope you have enjoyed this tutorial and found it useful. +Thank you! + + |