The Gawk Language in Linux

GAWK at the Linux Penguin

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GAWK

GAWK is the GNU implementation of the AWK language. This is the version we used in class. The awk and gawk languages are far more complex than the few little tasks demonstrated below, but this shows a basic introduction to what can be done with GAWK.

In the following demonstration, the instructor provided us with a simple text file that contained a list of all of the United States presidents, the number of president they were, the years they served, their vice presidents, and the state they were from. Then he gave us the task of using GAWK statements to extract and display specific pieces of data. Here are the results.

  • List all records containing Clinton

gawk ‘/Clinton/ {print $0}’ presidents.txt > lab2-1

This will find all records containing the word "Clinton" in the file named presidents.txt and add them to a file called lab2-1. You can then display the contents of the lab2-1 file using less lab2-1

Using GAWK Example 01

finding Presidents using GAWK

  • Which state has the most number of presidents?

gawk ‘{print $5}’ presidents.txt > lab2-2

Although I'm not showing the results, the answer is New York. The statement abobe is what I used to find that information.

  • Which presidents were born in the state of New York?

gawk –F “,” ‘/New York/ {print $1 “ “ $3}’ presidents.txt > lab2-3

This statement will find all presidents who were born in the state of New York in the file named presidents.txt and add them to a file called lab2-3. Then, using the less lab2-3 command, we can display the contents of the lab2-3 file.

Using GAWK Example 02

No Vice Presidents

  • Which presidents had no (None) vice presidents?

gawk –F “,” ‘/None/ {print $1 “ “ $4}’ presidents.txt > lab2-4

This statement will find all presidents who did not have a vice president by finding all records that contain the word "None" in the file named presidents.txt and add them to a file called lab2-4. Then, using the less lab2-4 command, we can display the contents of the lab2-4 file.

Using GAWK Example 03

More than one VP

  • How many presidents had more than one vice president?

Gawk –F “,” ‘/ and / {print $1 “ “ $3 “ ----> ” $4 “.”}’ presidents.txt > lab2-5

This statement will find all presidents who had more than one vice president by finding all records that contain the word "And" in the file named presidents.txt and add them to a file called lab2-5. Then, using the less lab2-5 command, we can display the contents of the lab2-5 file.

Using GAWK Example 04

Final Question

For the final question, the instructor wanted us to come up with our own question and then use a GAWK statement to find the answer to our question.

My question is: Which presidents were elected in the first year of a century? This would be the year they were elected, not the year they started their first term. Therefore, we are looking for the years 1800, 1900, and 2000. However, we know that the presidents.txt file does not contain such years because it identifies the years they “served”. For that reason, we look for the years ending in “01-“ (i.e. 1801, 1901 or 2001). Here is the gawk statement…

gawk –F “,” ‘/01-/ {print $1 “ “ $2 “ “ $3}’ presidents.txt > lab2-6

This could also be done using Logical OR statements like so (if you want to do it the long way)...

gawk –F “,” ‘/1801-/ || /1901-/ || /2001-/ {print $1 “ “ $2 “ “ $3}’ presidents.txt > lab2-6

This statement will find all records that contain "01-" in the years the president served. By doing this, we know that they were "elected" in the previous year (ending in "00"), because in the United States, a president is elected once every four years, but doesn't actually start his/her term of service until the following year. This identifies all presidents who were elected in the first year of a century.

Using GAWK Example 05

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