Construct detailed responses to the following prompts, synthesizing information from across the source document.

1. Compare and contrast the two methods for installing GAWK on a GNU/Linux system as described in the source: using a package manager versus installing from source code. Discuss the steps and commands involved in each process.
2. The source context describes a three-part structure for an AWK program (BEGIN, Body, END). Using examples from the text, explain the role of each part and how they work together to process a file like marks.txt.
3. Discuss the concept of built-in variables in AWK. Select five different standard built-in variables (e.g., NR, NF, FS, FILENAME, ARGC), explain their function, and describe their utility with examples provided in the source.
4. Explain AWK’s capabilities for handling regular expressions. Describe at least five different regular expression operators or special characters (e.g., ^, $, [], |, *) and provide an example for each based on the provided text.
5. Detail the control flow and looping structures available in AWK. Describe the if-else statement, the for loop, and the while loop, providing the syntax and an example for each as shown in the source material.