chore: integrated notions from articles on bash

knowledge base/awk.md

@@ -1,9 +1,41 @@
 # `awk`
 
+## Table of contents <!-- omit in toc -->
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+
+## TL;DR
+
+```sh
+# Print only the 3rd column.
+awk '{print $3}' sales.txt
+cat sales.txt | awk '{print $3}'
+
+# Print the 2nd and 3rd columns, separated with a comma.
+awk '{print $2 ", " $3}' sales.txt
+cat sales.txt | awk '{print $2 ", " $3}'
+
+# Print the sum of the 2nd and 3rd columns.
+awk '{print $2 + $3}' sales.txt
+
+# Print only lines with a length of more than 20 characters.
+awk 'length($0) > 20' sales.txt
+
+# Print only lines where the value of the second column is greater than 100.
+awk '$2 > 100' sales.txt
+```
+
 ## Further readings
 
 - [Print line only if number in third field is greater than X]
 - [Printing the last column of a line in a file]
+- [The essential Bash cheat sheet]
 
+<!-- project's references -->
+<!-- in-article references -->
+<!-- internal references -->
+<!-- external references -->
 [print line only if number in third field is greater than x]: https://unix.stackexchange.com/questions/395588/print-line-only-if-number-in-third-field-is-greater-than-x#395593
-[Printing the last column of a line in a file]: https://stackoverflow.com/questions/13046167/printing-the-last-column-of-a-line-in-a-file#13046224
+[printing the last column of a line in a file]: https://stackoverflow.com/questions/13046167/printing-the-last-column-of-a-line-in-a-file#13046224
+[the essential bash cheat sheet]: https://betterprogramming.pub/the-essential-bash-cheat-sheet-e1c3df06560