awk is a powerful programming language designed for text processing and typically used as a data extraction and reporting tool. It is named after its creators: Alfred Aho, Peter Weinberger, and Brian Kernighan. In this section, we will cover the basics of awk, its syntax, and how to use it effectively in Bash scripts.

1. Pattern-Action Statements: awk processes input data line by line and applies pattern-action statements to each line.
2. Fields and Records: awk treats each line of input as a record and each word or column within a line as a field.
3. Built-in Variables: awk has several built-in variables like NR (number of records), NF (number of fields), and more.
4. Operators and Functions: awk supports arithmetic, string, and logical operators, as well as built-in functions for text processing.

The basic syntax of an awk command is:

• pattern: Specifies the condition to match.
• action: Specifies what to do when the pattern matches.

Let's start with a simple example. Suppose we have a file data.txt with the following content:

To print the first and last names (fields 1 and 2), you can use:

Explanation:

• $1 and $2 refer to the first and second fields, respectively.
• The print statement outputs the specified fields.

To print only the records where the age (field 3) is greater than 25:

Explanation:

• $3 > 25 is the pattern that matches records where the third field is greater than 25.
• $0 refers to the entire line (record).

To print the line number along with each record:

Explanation:

• NR is a built-in variable that holds the current record number.

Given a file students.txt with the following content:

Write an awk command to print only the names of the students.

Solution:

Given the same students.txt file, write an awk command to print the names of students who scored more than 80.

Solution:

Given a file sales.txt with the following content:

Write an awk command to calculate the total sales.

Solution:

Explanation:

• sum += $1 adds the value of the first field to the sum variable for each record.
• END { print sum } prints the total sum after processing all records.

• Forgetting to quote the awk script: Always enclose the awk script in single quotes to prevent the shell from interpreting special characters.
• Using the wrong field separator: By default, awk uses spaces and tabs as field separators. Use the -F option to specify a different field separator if needed.
• Not using curly braces for actions: Always enclose actions in curly braces {} even if there is only one action.

In this section, we covered the basics of using awk for text processing in Bash. We learned about its syntax, how to print specific fields, filter records, and use built-in variables. We also practiced with some exercises to reinforce the concepts. In the next section, we will explore another powerful text processing tool: sed.