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Welcome to the spoken tutorial on  awk command.

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In this tutorial we will learn awk command.

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We will do this through some examples.

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To record this tutorial, I am using:

Ubuntu Linux 12.04 OS

GNU BASH v. 4.2.24

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Please note, GNU Bash version 4 or above is recommended to practice this tutorial.

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Let us start with an introduction to awk.

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The awk command is a very powerful text manipulation tool.

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It is named after its authors, Aho, Weinberger and Kernighan.

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It can perform several functions.

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It operates at the field level of a record.

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So, it can easily access and edit the individual fields of the record.

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Let us see some examples.

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For demonstration purpose, we use the awkdemo.txt file.

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Let us see the contents of awkdemo.txt file.

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Now open the terminal window by pressing Ctrl + Alt and T keys simultaneously on your keyboard.

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Let us see how to print using awk command.

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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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Press Enter.

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Here, Pass is the selection criteria.

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All the lines of the awkdemo where Pass occurs are printed.

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The action here is print.

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We can also use regular expressions in awk.

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Say, we want to print records of students with name "Mira."

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We would type:
awk space '/M (opening square bracket) [ ei (closing square bracket) ]*ra */{print}' space awkdemo.txt

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Press Enter.

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"*"   will give one or more occurrences of previous character.

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Thus, entries with more than one occurrence for i, e and a will be listed.

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For example,

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*Mira

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*Meera

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*Meeraa

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awk supports the extended regular expressions (ERE)

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Which means we can match multiple patterns separated by a PIPE.

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Let me clear the prompt.

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Now type:

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electrical(front slash)space (opening curly brackets)/{print}(closing curly brackets) after the quotes spaceawkdemo.txt

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Press Enter.

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Now entries for both "civil" and "electrical" are given.

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Let us go back to our slides.

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Parameters: awk has some special parameters to identify individual fields of a line.

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$1(Dollar 1) would indicate the first field.

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Similarly we can have $2, $3 and so on for respective fields.

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$0 represents the entire line.

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come back to our terminal.

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Note that each word is separated by PIPE in the file awkdemo.txt.

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In this case PIPE is called a delimiter.

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A delimiter separates words from each other.

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A delimiter can also be a single white space.

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To specify a delimiter, we have to give - capital F flag followed by a delimiter.

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Let us see.

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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

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Press Enter.

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This prints the entire line since we have used $0.

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Notice that names and stream of students are the second and third fields.

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Say we only want to print two fields.

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We will replace $0 with $2 and $3 in the above command.

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Press Enter .

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Only two fields are shown.

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Though it gives the right result, the display is all jagged and un-formatted.

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We can provide formatted output by using the C style printf statement.

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We can also provide a serial number by using a built-in variable NR.

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We will see more about built-in variables later.

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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 nâ?, after the double quotes  NR,$2,$3 closing curly bracket'  after the single quote space awkdemo.txt

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Press Enter.

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We see the difference.

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Here,  NR stands for number of records.

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Records are integers, hence we have written %d.

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Name and Stream are strings. So we have used %s.

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Here 25s will reserve 25 spaces for Name field.

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15s will reserve 15 spaces for Stream field.

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The minus sign is used to left justify the output.

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This brings us to the end of this tutorial.

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Let us move back to our slides.

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Let us summarize.

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In this tutorial we learnt: * To print using awk

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* Regular expression in awk * To list the entries for a particular stream

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* To list only the second and the third fields

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* To display a formatted output.

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As an assignment,

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display roll no., stream and marks of Ankit Saraf.

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Watch the video available at the link shown below.

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It summarizes the Spoken Tutorial project.

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If you do not have good bandwidth, you can download and watch it.

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More information on this Mission is available at:  [1]

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This is Ashwini Patil from IIT Bombay, signning off. Thank you for joining.