Linux-AWK/C2/Basics-of-awk/English-timed
From Script | Spoken-Tutorial
Revision as of 18:35, 20 February 2017 by Pratik kamble (Talk | contribs)
Time | Narration |
00:01 | Welcome to the spoken tutorial on 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:
Ubuntu Linux 12.04 OS GNU BASH v. 4.2.24 |
00:23 | Please note, GNU Bash version 4 or above is recommended to practice this tutorial. |
00:29 | Let us start with an introduction to awk. |
00:33 | The awk command is a very powerful text manipulation tool. |
00:38 | It is named after its authors, Aho, Weinberger and Kernighan. |
00:44 | It can perform several functions. |
00:46 | It operates at the field level of a record. |
00:51 | So, it can easily access and edit the individual fields of the record. |
00:56 | Let us see some examples. |
00:59 | For demonstration purpose, we use the awkdemo.txt file. |
01:04 | Let us see the contents of awkdemo.txt file. |
01:09 | Now open the terminal window by pressing Ctrl + Alt and T keys simultaneously on your keyboard. |
01:17 | Let us see how to print using awk command. |
01:22 | Type: awk space (within single quote) (front slash) '/Pass (front slash)/(opening curly bracket) {print (closing curly bracket)} (after the quotes) space awkdemo.txt |
01:38 | Press Enter. |
01:40 | Here, Pass is the selection criteria. |
01:44 | All the lines of the awkdemo where Pass occurs are printed. |
01:49 | The action here is print. |
01:52 | We can also use regular expressions in awk. |
01:56 | Say, we want to print records of students with name "Mira." |
02:01 | We would type:
awk space '/M (opening square bracket) [ ei (closing square bracket) ]*ra */{print}' space awkdemo.txt |
02:27 | Press Enter. |
02:29 | "*" will give one or more occurrences of previous character. |
02:33 | Thus, entries with more than one occurrence for i, e and a will be listed. |
02:40 | For example, |
02:42 | Mira with M I R A |
02:45 | Meera with M double E R A |
02:47 | and
Meeraa with M double E R double A |
02:52 | awk supports the extended regular expressions (ERE) |
02:58 | Which means we can match multiple patterns separated by a PIPE. |
03:03 | Let me clear the prompt. |
03:05 | Now type: |
03:06 | electrical(front slash)space (opening curly brackets)/{print}(closing curly brackets) after the quotes spaceawkdemo.txt |
03:23 | Press Enter. |
03:26 | Now entries for both "civil" and "electrical" are given. |
03:31 | Let us go back to our slides. |
03:34 | Parameters: awk has some special parameters to identify individual fields of a line. |
03:41 | $1(Dollar 1) would indicate the first field. |
03:45 | Similarly we can have $2, $3 and so on for respective fields. |
03:53 | $0 represents the entire line. |
03:56 | come back to our terminal. |
03:59 | Note that each word is separated by PIPE in the file awkdemo.txt. |
04:05 | In this case PIPE is called a delimiter. |
04:09 | A delimiter separates words from each other. |
04:13 | A delimiter can also be a single white space. |
04:16 | To specify a delimiter, we have to give - capital F flag followed by a delimiter. |
04:24 | Let us see. |
04:25 | 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 |
04:51 | Press Enter. |
04:53 | This prints the entire line since we have used $0. |
04:58 | Notice that names and stream of students are the second and third fields. |
05:04 | Say we only want to print two fields. |
05:08 | We will replace $0 with $2 and $3 in the above command. |
05:15 | Press Enter . |
05:18 | Only two fields are shown. |
05:21 | Though it gives the right result, the display is all jagged and un-formatted. |
05:26 | We can provide formatted output by using the C style printf statement. |
05:32 | We can also provide a serial number by using a built-in variable NR. |
05:40 | We will see more about built-in variables later. |
05:44 | 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 NR, $2, $3 closing curly bracket' after the single quote space awkdemo.txt |
06:33 | Press Enter. |
06:34 | We see the difference. |
06:37 | Here, NR stands for number of records. |
06:41 | Records are integers, hence we have written %d. |
06:45 | Name and Stream are strings. So we have used %s. |
06:50 | Here 25s will reserve 25 spaces for Name field. |
06:55 | 15s will reserve 15 spaces for Stream field. |
07:01 | The minus sign is used to left justify the output. |
07:05 | This brings us to the end of this tutorial. |
07:08 | Let us move back to our slides. |
07:10 | Let us summarize. |
07:11 | In this tutorial we learnt: * To print using awk |
07:16 | Regular expression in awk * To list the entries for a particular stream |
07:21 | To list only the second and the third fields |
07:24 | To display a formatted output. |
07:28 | As an assignment, |
07:29 | display roll no., stream and marks of Ankit Saraf. |
07:34 | Watch the video available at the link shown below. |
07:37 | It summarizes the Spoken Tutorial project. |
07:40 | If you do not have good bandwidth, you can download and watch it. |
07:45 | The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials. |
07:48 | Gives certificates to those who pass an online test. |
07:52 | For more details, please write to contact@spoken-tutorial.org |
07:58 | Spoken Tutorial Project is a part of the Talk to a Teacher project. |
08:01 | It is supported by the National Mission on Education through ICT,MHRD,Government of India. |
08:07 | More information on this Mission is available at: [1] |
08:12 | This is Ashwini Patil from IIT Bombay, signning off. Thank you for joining. |
Contributors and Content Editors
Nancyvarkey, PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14