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LINUX AWK Tutorial Series | Chapter 3

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LINUX AWK Tutorial Series | Chapter 3


Hello Everyone, Welcome Back...

In this chapter, let's get our hands dirty and start doing the basics.


Journey Begins

AWK will work on the field level of a record and that will help to do any operations on the individual fields.

example 1:




In this example, we are searching for a pattern "F" (Female Employees) from the Employee Data file and doing an action item which is "print"
Please observe that whatever search/action is performed those are on single quotes ''


If you remember the first chapter, that's how the AWK work.
Read file> Process lines > Search Pattern > Performs action



example 2:

Now AWK also can process records based on a regular expression.
Let's say I want to find all employee name starting with "Rob"






we are searching the pattern here which start with "Rob*". * means 0 or more characters.


example 3:

Now I want to find multiple patterns in a single file then we can use "|" pipe operator (or concatenate)



Here I am searching for Kevin and Alice in employee data and taking action as print.
We can use multiple patterns separated by "|"



Hope you have tried the above examples. Feel free to play around awk.

Parameters:

AWK will have various predefined parameters. These are special parameters that denote the specific fields of each record (line).

$1--> This will indicate the first field.
$2--> This will indicate the second field.
.... and so on for all the respective fields.

Question: Where is $0
Answer: $0 indicates the full lines which will have all fields.


AWK uses whitespaces as the default delimiter so our sample file is CSV which means comma-separated. So our delimiter would be "," in this case. 
Delimiter--> Separates 2 words/fields

So if we have to use a delimiter other than white space then we will use an option in AWK for a custom delimiter.

-F ','  --> It is hyphen capital F followed by the delimiter. If you are using space as a delimiter between words then no need to use this option.

So I will be using "-F" in our examples.


example 4:
Now I am going to use print $0.



Please notice I am using a custom delimiter and searching for Kevin, Alice, and Maria and printing the full line using $0.

Let's Say If I want to print only the Name, then that is the first field of each line. So we have to use $1.



Let's print the Name and Salary. Think and try.
Did you guessed it... No worries as per our delimiter ',' name is the first field and the salary is the 4th field.


Oh but look at the output that's Ugly, I didn't liked that!!!
What to do now

Now I am  going to use comma(,) between $1 and $4 which will put a by default delimiter in the output of AWK(Do you remember ?? Yes it was whitespace)


Now looks better than before, But if I want to add some custom message in between the output fields.


In the above screen shot, you can see, I am displaying a custom message in the output.
What does that mean
$1--> first field
,--> default delimiter(space)
"salary is"-->custom message string
,--> again default delimiter (space)
$4--> fourth field.


example 5:
If I don't want to search for any pattern and simply display all fields



Guess what I did here, just removed my search pattern.


Try doing this in your system.

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