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diff --git a/ult/ult_4/script.rst b/ult/ult_4/script.rst deleted file mode 100644 index 09de00e..0000000 --- a/ult/ult_4/script.rst +++ /dev/null @@ -1,409 +0,0 @@ -.. Objectives -.. ---------- - - .. At the end of this tutorial, you will be able to: - - .. 1. Understand what is Redirection and Piping. - .. 2. Learn various features of shell. - -.. Prerequisites -.. ------------- - -.. 1. Using Linux tools - Part 1 -.. 2. Using Linux tools - Part 2 -.. 3. Using Linux tools - Part 3 - -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 4'. - -.. L2 - -{{{ Show slide with objectives }}} - -.. R2 - -At the end of this tutorial, you will be able to, - - 1. Understand what is Redirection and Piping. - #. Learn various features of the shell. - -.. L3 - -{{{ Switch to the pre-requisite slide }}} - -.. R3 - -Before beginning this tutorial, we would suggest you to complete the -tutorial on "Using Linux tools from Part 1 to Part 3". - -.. R4 - -Let us begin with the concept of 'Redirection and Piping' which -performs the same operations as the ``cut`` and ``paste`` commands. - -Consider the files ``marks.txt`` and ``students.txt``.The contents of -the files are as following: - -.. L4 - -{{{ Open the terminal }}} -:: - - cat marks1.txt - cat students.txt - -.. R5 - -Now, let us view the contents of both these files side-by-side. - -.. L5 -:: - - cut -d " " -f 2- marks1.txt | paste -d " " students.txt - - -.. R6 - -Now, in order to view the same output in a new file at an other -location, we say, - -.. L6 -:: - - cut -d " " -f 2- marks1.txt > /tmp/m_tmp.txt - paste -d " " students.txt m_tmp.txt - -.. R7 - -First, let us try to understand the second solution,which is a two -step approach. -Later, we shall look at the first solution. - -.. L7 - -.. L8 - -{{{ Show slide, with Redirection }}} - -.. R8 - -The standard output, in general, goes to the display. -Hence, the output of the commands that we type, come out to the display. -This may not be what we always require. - -For instance, in the solution above, we use the cut command and get only -the required columns of the file and write the output to a new temporary -file. The ``>`` character is used to state that we wish to redirect the -output, and it is followed by the location to which we wish to redirect. -For example, - - command > file1 - -.. L9 - -{{{ Show slide, with Redirection... }}} - -.. R9 - -Similarly, the standard input (stdin) can be redirected as, - - command < file1 - -The input and the output redirection could be combined in a single command, -as, - - command < infile > outfile - -There is actually a third kind of standard stream, called the Standard -error (stderr). Any error messages that you get, are coming through this -stream. Like ``stdout``, ``stderr`` also streams to the display by default, -but it could be redirected to a file, as well. - -.. R10 - -For instance, let's reproduce an error using the ``cut`` command used -before. We shall change the ``-f`` option to ``-c`` - -.. L10 - -{{{ Switch to terminal }}} -:: - - cut -d " " -c 2- marks1.txt > /tmp/m_tmp.txt - -.. R11 - -This displays an error saying that the delimiter option should be used -with the fields option only. You may verify this by looking at the -``m_tmp.txt`` file, which is now empty.We can now, redirect the -``stderr`` also to a file, instead of showing it on the display. - -.. L11 -:: - - cut -d " " -f 2- marks1.txt 1> /tmp/m_tmp.txt 2> /tmp/m_err.txt - -.. R12 - -The above command redirects all the errors to the ``m_err.txt`` file -and the output to the ``m_tmp.txt`` file. When redirecting, 1 stands -for ``stdout`` and 2 stands for ``stderr``. - -Let us complete the solution by using the ``paste`` command. - -.. L12 -:: - - paste -d " " students.txt m_tmp.txt - -.. R13 - -So, in two steps we solved the problem of getting rid of the roll numbers -from the marks file and displaying the marks along with the names of the -students. Now, that we know how to redirect output, we could choose to -write the output to a file, instead of showing on the display. - -Let us now look at the first solution. - -.. L13 -:: - - cut -d " " -f 2- marks1.txt | paste -d " " students.txt - - -.. L14 - -{{{ Show slide, with Piping }}} - -.. R14 - -First of all, the hyphen at the end is to ask the paste command to -read the standard input, instead of looking for a FILE. The ``man`` -page of ``paste`` command gives us this information. - -The character ``|`` is called a pipe. -Now, let us observe the ``cut`` command. If we look at the command only -upto the ``|`` character, it appears as a normal ``cut`` command . -So, the ``|`` character here, seems -to be joining the two commands in some way. -Essentially, what we are doing is, to redirect the output of the first -command to ``stdin`` and the second command takes the input from the ``stdin``. - -More generally, - - command1 | command2 - -executes ``command1`` and sends it's output to the ``stdin``, which is then -used as the input for ``command2``. This activity is commonly called piping. - -.. L15 - -{{{ Show slide, with Piping... }}} - -.. R15 - -This is roughly equivalent to using two redirects and a temporary file. - - command1 > tempfile - command2 < tempfile - rm tempfile - -Also, given that a pipe is just a way to send the output of a command to -the ``stdin``, it should be obvious to you that we can use a chain of -pipes. Any number of commands can be piped together and therefore it should - be noted that it is not restricted to only two commands. - -The Bash shell has some nice features, that make our job of using the shell -easier and much more pleasant. Let us have a look at few of them here. - -Bash provides the feature of 'tab completion'. What does tab completion mean? -When you are typing a word, bash helps you to complete the word. -This can be done by entering some portion of the word and thereafter, -pressing the tab key. - -If you do not get the desired word on pressing the tab key, it implies that -either the word doesn't exist or the word cannot be decided unambiguously. -In the latter case, pressing the tab key for a second time,will list out -all the possibilities. - -.. L16 - -{{{ Show slide, with Tab-completion }}} - -.. R16 - -Bash provides tab completion for the following. - - 1. File Names - 2. Directory Names - 3. Executable Names - 4. User Names (when they are prefixed with a ~) - 5. Host Names (when they are prefixed with a @) - 6. Variable Names (when they are prefixed with a $) - -.. R17 - -For example, - -.. L17 - -{{{ Switch to terminal }}} -:: - - pas<TAB><TAB> - ~/<TAB><TAB> - -.. R18 - -Bash also saves the history of the commands you have typed earlier. -This feature enables you to goto the previously typed commands and -use them as and when necessary. The up and down arrow keys will help -you to navigate -through these commands in the bash history. - -.. L18 -:: - - <UP-ARROW> - -.. R19 - -You may also search incrementally, for commands in your bash history. -``Ctrl-r`` searches for the commands that you have typed earlier. However, -it should be noted that the number of commands saved in the history is -limited, generally upto a 1000 commands. - -.. L19 -:: - - <Ctrl-r> pas - -.. R20 - -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 a blank space. -For this reason, it is always recommended to use only the characters A-Z, -a-z, 0-9, period, dash and underscore, when naming files and -directories on Unix. If your file or directory has a shell meta character -in the name, you may find it difficult to use this name in a shell command. - -.. L20 - -.. L21 - -{{{ Show slide, with Shell Meta Characters }}} - -.. R21 - -The characters that you see on the slide are the shell meta characters - -.. R22 - -Lets take an example, - -.. L22 - -{{{ Switch to terminal }}} -:: - - ls file.? - -.. R23 - -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, - -.. L23 -:: - - ls file.? - -.. R24 - -Run on the same directory would only list file.c because the ? only matches -one character, no more, no less. This helps you save time, while typing. - -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 - -.. L24 -:: - - more c* - -.. R25 - -Here, the c* matches that long file name. -File-names containing meta characters can pose many problems and should -never be intentionally created. - -.. L25 - -.. L26 - -{{{ Switch to Summary slide }}} - -.. R26 - -This brings us to the end of the end of this tutorial. -In this tutorial, we have learnt to, - - 1. Use the ``cut`` and ``paste`` commands in redirection. - 2. Use the pipe ( | ) character. - 3. Implement features of shell, like tab-completion and history. - -.. L27 - -{{{ Show self assessment questions slide }}} - -.. R27 - -Here are some self assessment questions for you to solve: - - 1. Bash does not provide tab completion for Host Names. - True of False? - - 2. In a file /home/test.txt ,first line is "data:myscripts:20:30". How do we - view only the minutes (last field, 30). - - - cut -d : -f 4 /home/test.txt - - cut -f 3 /home/test.txt - - cut -d : -f 3 /home/test.txt - - None of these - -.. L28 - -{{{ Solutions for the self assessment questions on slide }}} - -.. R28 - -And the answers: - - 1. False. Bash provides tab completion for Host Names when they are prefixed - with a @ sign. - - 2. The correct option would be -:: - - cut -d : -f 4 /home/test.txt - -.. L29 - -{{{ Show the Thank you slide }}} - -.. R29 - -Hope you have enjoyed this tutorial and found it useful. -Thank you! - |