Option v

Learn how to leverage AWK’s -v flag to declare variables before program execution. This enhances script flexibility, readability, and maintainability.

Table of Contents

• What Is -v in AWK?
• Basic Syntax and Examples
• Combining -v with Other Options
• Sample Data: employees.txt
• Practical Examples
  • 1. Prefixing First Names
  • 2. Filtering High Earners
  • 3. Printing Only First Names
  • 4. Advanced: Multiple Salary Thresholds
• Common AWK Options
• Summary
• References

What Is -v in AWK?

The -v option in AWK allows you to assign a value to a variable before the AWK program starts. Variables declared this way can be used in BEGIN, END, or pattern/action blocks—similar to command-line parameters in other scripting languages.

Basic Syntax and Examples

awk -v var="Hello, World!" 'BEGIN { print var }'

• -v var="Hello, World!" assigns the string to var.
• BEGIN { ... } runs before any input is read.
• print var outputs the variable’s value.

Example output:

$ awk -v var="Hello, World!" 'BEGIN { print var }'
Hello, World!

Combining -v with Other Options

When using multiple flags, the order matters. According to the AWK usage:

usage: awk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]

Always specify -F (field separator) before -v:

awk -F "|" -v var="Hello, World!" 'BEGIN { print var }'

Sample Data: employees.txt

$ cat employees.txt
1|Kriti|Shreshtha|Finance|Financial Analyst|[email protected]|60000
2|Rajasekar|Vasudevan|Financial|Senior Accountant|[email protected]|75000
3|Debbie|Miller|IT|Software Developer|[email protected]|80000
4|Enrique|Rivera|Marketing|Marketing Specialist|[email protected]|65000
5|Feng|Lin|Sales|Sales Manager|[email protected]|90000
6|Andy|Luscomb|IT|IT Manager|[email protected]|95000
7|Mark|Crocker|HR|HR Manager|[email protected]|85000
8|Jing|Ma|Engineering|Engineering Manager|[email protected]|100000

Practical Examples

1. Prefixing First Names

Use a prefix variable to label each first name:

$ awk -F "|" -v prefix="Employee's First Name: " \
    '{ print prefix, $2 }' employees.txt

Output:

Employee's First Name: Kriti
Employee's First Name: Rajasekar
...
Employee's First Name: Jing

2. Filtering High Earners

Without Variables

$ awk -F "|" '$7 >= 90000' employees.txt

With -v Variable

$ awk -F "|" -v high_salary=90000 \
    '$7 >= high_salary' employees.txt

3. Printing Only First Names

Combine the salary threshold with a print action:

$ awk -F "|" -v high_salary=90000 \
    '$7 >= high_salary { print $2 }' employees.txt

Result:

Feng
Andy
Jing

4. Advanced: Multiple Salary Thresholds

Declare both high and low benchmarks:

$ awk -F "|" \
    -v high_salary=90000 \
    -v low_salary=65000 \
    '$7 >= high_salary || $7 <= low_salary { print $2 }' employees.txt

This returns first names earning ≤ 65000 or ≥ 90000.

Common AWK Options

Summary

• Use -v to assign variables before AWK starts.
• Always put -F before -v to avoid parsing errors.
• Variables can appear in BEGIN, pattern/actions, and END blocks.
• Meaningful variable names improve script readability and maintainability.

References

• GNU AWK Manual
• AWK Tutorial
• Kubernetes Documentation
• Docker Hub