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diff --git a/ult/ult_3/script.rst b/ult/ult_3/script.rst deleted file mode 100644 index adc24b8..0000000 --- a/ult/ult_3/script.rst +++ /dev/null @@ -1,375 +0,0 @@ -.. Objectives -.. ---------- - - .. At the end of this tutorial, you will be able to: - - .. 1. Display the contents of files. - .. 2. Read only parts of a file. - .. 3. Look at the statistical information of a file. - -.. Prerequisites -.. ------------- - -.. 1. Using Linux tools - Part 1 -.. 2. Using Linux tools - Part 2 - -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 -'Using linux tools - Part 3'. - -.. L2 - -{{{ Show slide with objectives }}} - -.. R2 - -At the end of this tutorial, you will be able to, - - 1. Display the contents of files. - #. Read only parts of a file. - #. Look at the statistical information of a file. - -.. L3 - -{{{ Switch to the pre-requisite slide }}} - -.. R3 - -Before beginning this tutorial,we would suggest you to complete the -tutorial on "Using Linux tools - Part 1" and "Using Linux tools - Part 2". - -.. R4 - -Let us begin with how to read a while as a whole. -The ``cat`` command is the most commonly used command to display the -contents of files. To view the contents of a file, say, ``foo.txt``, we -simply say, - -.. L4 -:: - - cat foo.txt - -.. R5 - -You can see the contents of the file on the terminal. - -The cat command could also be used to concatenate the text of multiple -files. Say, we have two files,``foo.txt`` and ``bar.txt``, - -.. L5 -:: - - cat foo.txt bar.txt - -.. R6 - -It shows the output of both the files concatenated on the standard output. -But if we had a long file,the output of ``cat`` command is not convenient -to read. -Let's look at the ``less`` command which turns out to be more useful in -such a case. - -``less `` allows you to view the contents of a text file one screen at a -time. - -.. L6 -:: - - less wonderland.txt - -.. R7 - -This shows us the file, one screen at a time. - -.. L7 - -.. L8 - -{{{ Show slide with, less }}} - -.. R8 - -``less`` has a list of commands that it allows you to use, once you have -started viewing a file. A few of the common ones have been listed below. - - * q: Quit. - - * [Arrows]/[Page Up]/[Page Down]/[Home]/[End]: Navigation. - - * ng: Jump to line number n. Default is the start of the file. - - * /pattern: Search for pattern. Regular expressions can be used. - - * h: Help. - -.. R9 - -Let us move ahead with the topic. Often we just would like to get some -statistical information about the file, rather than viewing the contents -of the file. The ``wc`` command prints these details for a file. - -.. L9 -:: - - wc wonderland.txt - -.. L10 - -{{{ Highlight the required portions accordingly while narrating }}} - -.. R10 - -As you can see, we get some information about the file. -The first number is the number of lines, the second is the number of words -and the third is the number of characters in the file. - -.. R11 - -Let us now look at a couple of commands that let you see parts of files, -instead of the whole file. The ``head`` and ``tail`` commands let you see -parts of files, as their names suggest, the start and the end of a file, -respectively. - -.. L11 -:: - - head wonderland.txt - -.. R12 - -It prints only the first 10 lines of the file. Similarly tail will print the -last 10 lines of the file. If we wish to change the number of lines that we -wish to view, we use the option ``-n``. - -.. L12 -:: - - head -n 1 wonderland.txt - -.. R13 - -It prints only the first line of the file. Similarly, we could print only -the last line of the file. - -The most common use of the tail command is to monitor a continuously -changing file, for instance a log file. Say you have a process running, -which is continuously logging it's information to a file, for instance the -logs of the system messages. - -.. L13 -:: - - tail -f /var/log/dmesg - -.. R14 - -This will show the last 10 lines of the file as expected, but along with -that, it starts monitoring the file. Any new lines added at the end of the -file, will be shown. To interrupt tail, while it is monitoring, hit -``Ctrl-C``. which will stop any process that is running from your -current shell. - -We looked at a couple of functions that allowed us to view a part of a file, -line-wise. We shall now look at a couple of commands that will allow us to look -at only certain sections of each line of a file and merge those parts. -Let's take the ``/etc/passwd`` file as our example file. It contains -information about each user of the system. - -.. L14 -:: - - cat /etc/passwd - -.. R15 - -In the output, let us look at only the first, fifth, sixth and the last -columns.The first column is the user name, the fifth column is the user info, -the sixth column is the home folder and the last column is the path of the -shell program that the user uses. -Let's say we wish to look at only the user names of all the users in the -file, how do we do it? - -.. L15 -:: - - cut -d : -f 1 /etc/passwd - -.. R16 - -It gives us the required output. Let us understand this operation in detail. -The first option ``-d`` specifies the delimiter between the various fields in -the file, in this case it is the semicolon. If no delimiter is specified, -the TAB character is assumed to be the delimiter. The ``-f`` option specifies, -the field number that we want to choose. -You can print multiple fields, by separating the field numbers with a -comma. - -Pause the video here, try out the following exercise and resume the video. - -.. L16 - -.. L17 - -{{{ Show slide with exercise 3 }}} - -.. R17 - -Print only the first, fifth and the seventh fields of the file ``/etc/passwd``. - -.. R18 - -Switch to the terminal for solution - -.. L18 - -{{{ continue from paused state }}} -{{{ Switch to the terminal }}} - -:: - - cut -d : -f 1,5,7 /etc/passwd - -.. R19 - -We get the correct output. -Instead of choosing by fields, ``cut`` also allows us to choose on the -basis of characters or bytes. For instance, we could get the first 4 -characters of all the entries of the file, ``/etc/passwd`` by saying, - -.. L19 -:: - - cut -c 1-4 /etc/passwd - -.. R20 - -The end limits of the ranges can take sensible default values, if they are -left out. For example, - -.. L20 -:: - - cut -c -4 /etc/passwd - -.. R21 - -It gives the same output as before. If the start position has not been -specified, it is assumed to be the start of the line. Similarly if the end -position is not specified, it is assumed to be the end of the line. - -.. L21 -:: - - cut -c 10- /etc/passwd - -.. R22 - -It prints all the characters from the 10th character up to the end of the -line. -Let us now solve an inverse problem. Let's say we have two columns of data -in two different files, and we wish to view them side by side. - -.. L22 - -.. L23 - -{{{ Show slide with, paste }}} - -.. R23 - -For instance, given a file containing the names of students in a file, -students.txt, and another file with the marks of the students,marks.txt, - -.. R24 - -we wish to view the contents, side by side. The ``paste`` command allows -us to do that. - -.. L24 -:: - - paste students.txt marks.txt - paste -s students.txt marks.txt - -.. R25 - -The first command gives us the output of the two files, next to each other -and the second command gives us the output one below the other. - -Now, this problem is a bit unrealistic because, we wouldn't have the marks -of students in a file, without any information about the student to which -they belong. Let's say our marks file had the first column as the roll -number of the student, followed by the marks of the students. What would we -then do, to get the same output that we got before? - -Essentially we need to use both, the ``cut`` and ``paste`` commands, but -how do we do that? That brings us to the concept of Redirection and Piping -which is covered in the next spoken tutorial. - -.. L25 - -.. L26 - -{{{ Switch to summary slide }}} - -.. R26 - -This brings us to the end of this tutorial. -In this tutorial, we have learnt to, - - 1. Display the contents of files using the ``cat`` command. - #. View the contents of a file one screen at a time using the - ``less`` command. - #. Display specific contents of file using the ``head`` and - ``tail`` commands. - #. Use the ``cut``, ``paste`` and ``wc`` commands. - -.. L27 - -{{{ Show self assessment questions slide }}} - -.. R27 - -Here are some self assessment questions for you to solve - -1. How to view lines from 1 to 15 in wonderland.txt? - -2. In ``cut`` command, how to specify space as the delimiter? - -.. L28 - -{{{ Solution of self assessment questions on slide }}} - -.. R28 - -And the answers, - -1. We can use the head command as, -:: - - head -15 wonderland.txt - -2. We use the -d option with the command as, -:: - - cut -d " " <filename> - -.. L29 - -{{{ Show the Thank you slide }}} - -.. R29 - -Hope you have enjoyed this tutorial and found it useful. -Thank you! - |