Difference between revisions of "BOSS-Linux/C3/Basics-of-awk/English-timed"
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| − | | Let us see how to print using '''awk command.''' | + | | Let us see how to print using ''''awk' command.''' |
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| − | | Type: '''awk space''' | + | | Type: '''awk space''' within single quote front-slash '''Pass ''' front- slash opening curly bracket '''print''' closing curly bracket (after the quotes) '''space awkdemo.txt''' |
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| − | | We would type: '''awk space''' within single quotes ''' | + | | We would type: '''awk space''' within single quotes front-slash capital '''M''' (/M) opening square-bracket ''' ei''' closing square-bracket asterisk-sign '''ra''' asterisk-sign front-slash space opening curly-bracket '''print''' closing-curly bracket after the quotes '''space awkdemo.txt''' |
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Revision as of 20:13, 13 August 2015
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on the awk command. |
| 00:05 | In this tutorial, we will learn 'awk' command. |
| 00:09 | We will do this through some examples. |
| 00:12 | To record this tutorial, I am using:
|
| 00:21 | Please note, GNU Bash version 4 or above is recommended to practice this tutorial. |
| 00:29 | Let us start with an introduction to awk. |
| 00:32 | The awk command is a very powerful text manipulation tool. |
| 00:36 | It is named after its authors, Aho, Weinberger and Kernighan. |
| 00:42 | It can perform several functions. |
| 00:46 | It operates at the field level of a record. |
| 00:49 | So, it can easily access and edit the individual fields of the record. |
| 00:56 | Let us see some examples. |
| 00:58 | For demonstration purpose, we use the awkdemo.txt file. |
| 01:03 | Let us see the contents of awkdemo.txt file. |
| 01:07 | Now, open the terminal window. |
| 01:10 | Let us see how to print using 'awk' command. |
| 01:15 | Type: awk space within single quote front-slash Pass front- slash opening curly bracket print closing curly bracket (after the quotes) space awkdemo.txt |
| 01:32 | press Enter. |
| 01:34 | Here, Pass is the selection criteria. |
| 01:38 | All the lines of the awkdemo where Pass occurs are printed. |
| 01:43 | The action here is print. |
| 01:46 | We can also use regular expressions in awk. |
| 01:50 | Say, we want to print records of students with name Mira. |
| 01:55 | We would type: awk space within single quotes front-slash capital M (/M) opening square-bracket ei closing square-bracket asterisk-sign ra asterisk-sign front-slash space opening curly-bracket print closing-curly bracket after the quotes space awkdemo.txt |
| 02:20 | Press Enter. |
| 02:22 | *(asterisk) will give one or more occurrences of previous character. |
| 02:27 | Thus, entries with more than one occurrence for i, e and a will be listed. |
| 02:34 | For example- |
| 02:35 | * Mira (with 'M' 'I' 'R' 'A') |
| 02:38 | * Meera(with 'M' 'E' 'E' 'R' 'A') |
| 02:41 | * Meeraa(with M E E R A A ) |
| 02:45 | awk supports the extended regular expressions (ERE) |
| 02:51 | which means we can match multiple patterns separated by a PIPE. |
| 02:56 | Let me clear the prompt. |
| 02:59 | Now, type: |
| 03:00 | ) electrical front slash space opening curly bracket print closing curly bracket after the quotes space awkdemo.txt |
| 03:18 | Press Enter. |
| 03:19 | Now, entries for both civil and electrical are given. |
| 03:24 | Let us go back to our slides. |
| 03:28 | Parameters: awk has some special parameters to identify individual fields of a line. |
| 03:36 | $1 (Dollar 1) would indicate the first field. |
| 03:40 | Similarly, we can have $2, $3 and so on for respective fields. |
| 03:47 | $0 represents the entire line. |
| 03:50 | come back to our terminal. |
| 03:52 | Note that each word is separated by PIPE in the file awkdemo.txt. |
| 03:59 | In this case, PIPE is called a delimiter. |
| 04:03 | A delimiter separates words from each other. |
| 04:06 | A delimiter can also be a single white space. |
| 04:11 | To specify a delimiter, we have to give '-F' (capital F) flag followed by a delimiter. |
| 04:18 | Let us see. |
| 04:19 | Type: awk space minus (capital) F space within double quotes PIPE space within single quote front slash civil PIPE electrical front slash opening curly bracket print space dollar0 closing curly bracket after the quotes space awkdemo.txt |
| 04:44 | Press Enter. |
| 04:46 | This prints the entire line since we have used $0. |
| 04:52 | Notice that names and stream of students are the second and third fields. |
| 04:58 | Say, we only want to print two fields. |
| 05:01 | We will replace $0 with $2 and $3 in the above command. |
| 05:09 | Press Enter . |
| 05:11 | Only two fields are shown. |
| 05:14 | Though it gives the right result, the display is all jagged and un-formatted. |
| 05:20 | We can provide formatted output by using the C style printf statement. |
| 05:26 | We can also provide a serial number by using a builtin variable NR. |
| 05:33 | We will see more about builtin variables later. |
| 05:37 | Now, type: awk space minus (capital) F within double quotes Pipe after the double quotes space 'front slash Pass front slash opening curly-bracket printf within double quotes percentage- sign 4d space percentage-sign -25s space percentage-sign minus 15s space backslash n, after the double quotes comma NR, $2, $3 closing curly bracket' after the single quote space awkdemo.txt |
| 06:25 | Press Enter. |
| 06:28 | We see the difference. |
| 06:30 | Here, NR stands for number of records. |
| 06:33 | Records are integers, hence we have written %d. |
| 06:37 | Name and Stream are strings. So we have used %s. |
| 06:43 | Here, 25s will reserve 25 spaces for Name field. |
| 06:48 | 15s will reserve 15 spaces for Stream field. |
| 06:54 | The minus sign is used to left justify the output. |
| 06:58 | This brings us to the end of this tutorial. |
| 07:01 | Let us move back to our slides. |
| 07:04 | Let us summarize. |
| 07:05 | In this tutorial, we learnt: * To print using awk |
| 07:10 | * Regular expression in awk * To list the entries for a particular stream |
| 07:15 | * To list only the second and the third fields |
| 07:18 | * To display a formatted output. |
| 07:19 | As an assignment, |
| 07:22 | Display roll no., stream and marks of Ankti Saraf |
| 07:27 | Watch the video available at the link shown below. |
| 07:30 | It summarizes the Spoken Tutorial project. |
| 07:33 | If you do not have good bandwidth, you can download and watch it. |
| 07:37 | The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials. |
| 07:42 | Gives certificates to those who pass an online test. |
| 07:45 | For more details, please write to contact@spoken-tutorial.org |
| 07:51 | Spoken Tutorial Project is a part of the Talk to a Teacher project. |
| 07:55 | It is supported by the National Mission on Education through ICT,MHRD,Government of India. |
| 08:02 | More information on this mission is available at: [1] |
| 08:07 | This is Ashwini Patil from IIT Bombay, signing off. Thank you for joining. |
