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diff --git a/ult/ult_6/script.rst b/ult/ult_6/script.rst index 0413ada..020f3a6 100644 --- a/ult/ult_6/script.rst +++ b/ult/ult_6/script.rst @@ -3,19 +3,15 @@ .. 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. + .. 1. Understand various features of shell + .. 2. Learn about shell meta characters .. Prerequisites .. ------------- -.. 1. Using Linux tools - Part 1 -.. 2. Using Linux tools - Part 2 -.. 3. Using Linux tools - Part 3 -.. 4. Using Linux tools - Part 4 -.. 5. Using Linux tools - Part 5 - +.. 1. Getting started with Linux +.. 2. Basic File Handling +.. 4. Advanced file handling Script ------ @@ -28,7 +24,7 @@ team along with the logo of MHRD }}} .. R1 Hello friends and Welcome to the tutorial on -'Using linux tools - Part 6'. +'Redirection and Piping'. .. L2 @@ -38,9 +34,8 @@ Hello friends and Welcome to the tutorial on 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. + 1. Understand various features of shell + #. Learn about shell meta characters .. L3 @@ -49,248 +44,236 @@ At the end of this tutorial, you will be able to, .. R3 Before beginning this tutorial,we would suggest you to complete the -tutorial on "Using Linux tools from Part 1 to Part 5". +former tutorials as being displayed currently. + +.. L4 -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``. +{{{ Show slide, with Tab-completion }}} .. R4 -We open our editor and save the following text to ``results.sh`` +The Bash shell has some nice features, that make our job of using the shell +easier and much more pleasant. We shall look at a few of them, here. -.. L4 -{{{ Open an editor and type the following }}} -:: +Bash provides the feature of tab completion. What does tab completion mean? +When you are trying to type a word, bash can complete the word for you, if you +have entered enough portion of the word (to complete it unambiguously) and +then hit the tab key. - #!/bin/bash - mkdir ~/marks - cut -d " " -f 2- marks1.txt | paste -d " " students.txt - | sort > ~/marks/results.txt +If on hitting the tab key, the word doesn't get completed, either the word +doesn't exist or the word cannot be decided unambiguously. If the case is the +latter one, hitting the tab key a second time, will list the possibilities. -.. R5 +.. L5 -We can now run the script as, +{{{ Show slide, with Tab-completion.. }}} -.. L5 +.. R5 -{{{ Open the terminal }}} -:: +Bash provides tab completion for the following. - ./results.sh + File Names + Directory Names + Executable Names + User Names (when they are prefixed with a ~) + Host Names (when they are prefixed with a @) + Variable Names (when they are prefixed with a $) .. R6 -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. +For example, .. L6 -:: - - chmod u+x results.sh - ./results.sh -.. R7 +{{{ Switch to terminal }}} +:: -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 our -``results.sh`` script, as follows. + pas<TAB><TAB> + PA<TAB> + ~/<TAB><TAB> .. L7 -{{{ Open an editor and type the following }}} -:: +{{{ Show slide, with History }}} - #!/bin/bash - mkdir ~/marks - cut -d " " -f 2- marks1.txt | paste -d " " students.txt - | sort > ~/marks/results.txt - echo "Results generated." - -.. R8 - -Now, on running the script, we get a message on the screen informing us, -when the script has run. +.. R7 -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. +Bash also saves the history of the commands you have typed. So, you can go +back to a previously typed command. Use the up and down arrow keys to navigate +in your bash history. +You can also search incrementally, for commands in your bash history. Ctrl-r +search for the commands that you have typed before. But, note that the number +of commands saved in the history is limited, generally upto a 1000 commands. .. L8 -{{{ Make the necessary changes in the previous script }}} - +{{{ Switch to terminal }}} :: - #!/bin/bash - mkdir ~/marks - cut -d " " -f 2- marks1.txt | paste -d " " students.txt - | sort > ~/marks/$1 - echo "Results generated." + <Ctrl-r> pas +.. R8 -{{{ Highlight the text ``$1`` }}} +.. L9 + +{{{ Show slide, with Shell Meta Characters }}} .. R9 -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``. +Unix recognizes certain special characters, called "meta characters," as +command directives. The shell meta characters are recognized anywhere they +appear in the command line, even if they are not surrounded by blank space. +For that reason, it is safest to only use the characters A-Z, a-z, 0-9, and +the period, dash, and underscore characters when naming files and directories + on Unix. If your file or directory has a shell meta character in the name, +you will find it difficult to use the name in a shell command. -.. L9 -:: +The characters that you see on the slide are the shell meta characters - ./results.sh grades.txt + / < > ! $ % ^ & * | { } [ ] " ' ` ~ ; .. R10 -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. +Let's take an example, .. L10 -.. L11 +{{{ Switch to terminal }}} +:: -{{{ Show slide, PATH }}} + ls file.* .. R11 -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. +It means, run on a directory containing the files file, file.c, file.lst, and +myfile would list the files file.c and file.lst. However, -.. L12 +.. L11 -{{{ Switch to the terminal }}} :: - echo $PATH + ls file.? .. R12 -So, these are all the paths that are searched, when looking to execute a -command. If we put the results.sh script in one of these locations, we -could simply run it, without using the ``./`` at the beginning. +Run on the same directory would only list file.c because the ? only +matches one character, no more, no less. This can save you a great deal of +typing time. -.. L13 +For example, if there is a file called california_cornish_hens_with_wild_rice +and no other files whose names begin with 'c', you could view the file without +typing the whole name by typing this + +.. L12 + +:: -{{{ Show slide, variables & comments }}} + more c* .. R13 -As expected, it is possible to define our own variables inside our shell -scripts. For example, +Here, the c* matches that long file name. -.. L14 +File-names containing metacharacters can pose many problems and should never +be intentionally created. -{{{ Switch to the terminal }}} -:: +.. L13 - name="FOSSEE" +.. L14 + +{{{ Switch to Summary slide }}} .. R14 -It creates a new variable ``name`` whose value is ``FOSSEE``. To refer to this -variable, inside our shell script, we would refer to it, as ``$name``. -Note that, there is no space around the ``=`` sign. +This brings us to the end of the end of this tutorial. +In this tutorial, we have learnt to, +1. Implement features of tab-completion and history. +#. Make use of the shell meta characters. + .. L15 -:: - - ls $name* + +{{{ Show self assessment questions slide }}} .. R15 -.. R16 +Here are some self assessment questions for you to solve: -It is possible to store the output of a command in a variable, by enclosing -the command in back-quotes. +1. Bash does not provide tab completion for Host Names. True of False? + +2. State the command which will list all the files in the current working + directory that end in either .c or .h .. L16 -:: - count=`wc -l wonderland.txt` +{{{ Solutions for the self assessment questions on slide }}} -.. R17 +.. R16 -It saves the number of lines in the file ``wonderland.txt`` in the variable -count. +And the answers: -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. +1. False. Bash provides tab completion for Host Names when they are prefixed + with a @ sign. -.. L18 + +2. The command which will find the files ending either in .c or .h is, +:: -.. L19 + ls *.[ch] -{{{ Switch to 'Summary' slide }}} -.. R19 +.. L17 -This brings us to the end of the end of this tutorial. -In this tutorial, we have learnt to, +{{{ Show the SDES & FOSSEE slide }}} - 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. +.. R17 -.. L20 +Software Development techniques for Engineers and Scientists - SDES, is an +initiative by FOSSEE. For more information, please visit the given link. -{{{ Show self assessment questions slide }}} +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. -.. R20 +.. L18 -Here are some self assessment questions for you to solve +{{{ Show the ``About the Spoken Tutorial Project'' slide }}} - 1. Which sign is used to comment out content from a shell script. - - - $ - - % - - # - - * +.. R18 - 2. How will you add directory ``/data/myscripts`` to the beginning of - the $PATH environment variable ? +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. -.. L21 +.. L19 -{{{ Solution of self assessment questions on slide }}} +{{{ Show the `` Spoken Tutorial Workshops'' slide }}} -.. R21 +.. R19 -And the answers, +The Spoken Tutorial Project Team conducts workshops using spoken tutorials, +gives certificates to those who pass an online test. - 1. We use the ``#`` sign to comment out the content from a shell script. +For more details, contact contact@spoken-tutorial.org - 2. In order to add a directory to the beginning of the $PATH variable,we - say, -:: +.. L20 - $PATH=/data/myscripts:$PATH +{{{ Show the ``Acknowledgements'' slide }}} -.. L22 +.. R20 + +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. + +.. L21 {{{ Show the Thank you slide }}} -.. R22 +.. R21 Hope you have enjoyed this tutorial and found it useful. Thank you! - - |