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awk commands with practical examples

AWK is a powerful text-processing tool in Linux and Unix. It is used for pattern scanning and processing. Below are some commonly used awk commands with practical examples.

1. What is AWK?

  • AWK is a scripting language designed for text processing and pattern matching.
  • It processes structured data such as CSV, logs, and space/tab-separated files.
  • AWK reads a file line by line, splits each line into fields, and applies specified operations.

2. Basic Syntax

The basic syntax of an awk command is:

bash
awk 'pattern { action }' filename
  • pattern – Specifies when to apply the action.
  • action – Specifies what to do (print, calculate, modify, etc.).
  • filename – The input file.

3. Print a File’s Content

bash
awk '{print}' employees.txt
  • This prints every line of employees.txt, similar to cat employees.txt.

4. Print Specific Columns

bash
awk '{print $1, $3}' employees.txt
  • $1, $2, $3, etc., represent columns (fields).
  • Example (employees.txt file):
    yaml
    1 John 5000
    2 Alice 6000
    3 Bob 7000
  • Output:
    yaml
    1 5000
    2 6000
    3 7000

5. Print Lines Matching a Pattern

bash
awk '/Alice/ {print}' employees.txt
  • Finds and prints lines containing “Alice”.

6. Print Lines Based on a Condition

bash
awk '$3 > 5000 {print $1, $2}' employees.txt
  • Prints employees with a salary greater than 5000.
  • Output:
    2 Alice
    3 Bob

7. Count the Number of Lines

bash
awk 'END {print NR}' employees.txt
  • NR (Number of Records) holds the count of processed lines.
  • Output:
    3

8. Calculate Sum of a Column

bash
awk '{sum += $3} END {print "Total Salary:", sum}' employees.txt
  • Adds up all values in the third column.
  • Output:
    yaml
    Total Salary: 18000

9. Use a Custom Field Separator

For a CSV file (employees.csv):

1,John,5000
2,Alice,6000
3,Bob,7000

Use -F to define the field separator:

bash
awk -F ',' '{print $1, $3}' employees.csv
  • Output:
    yaml
    1 5000
    2 6000
    3 7000

10. Print Only Even Rows

bash
awk 'NR%2==0' employees.txt
  • Prints only even-numbered lines.

11. Find Maximum Salary

bash
awk 'max < $3 {max=$3} END {print "Max Salary:", max}' employees.txt
  • Finds the highest salary.

12. AWK with Piping

bash
ls -l | awk '{print $9, $5}'
  • Displays filenames and their sizes.

13. Replace a Column Value

bash
awk '{$2="David"; print}' employees.txt
  • Replaces the second column with “David”.

1. Print Specific Columns from a File

Command:

bash
awk '{print $1, $3}' file.txt

Explanation:
Prints the first and third columns of file.txt.
Example:

yaml
$ cat employees.txt
1 John 5000
2 Alice 6000
3 Bob 7000

$ awk '{print $1, $3}' employees.txt
1 5000
2 6000
3 7000

2. Print Lines Matching a Pattern

Command:

bash
awk '/Alice/ {print}' employees.txt

Explanation:
Prints lines containing the word “Alice”.
Example Output:

yaml
2 Alice 6000

3. Print Lines with a Condition (Salary > 5000)

Command:

bash
awk '$3 > 5000 {print $1, $2}' employees.txt

Explanation:
Prints employees with salaries greater than 5000. Example Output:

2 Alice
3 Bob

4. Print the Sum of a Column

Command:

bash
awk '{sum += $3} END {print "Total Salary:", sum}' employees.txt

Explanation:
Calculates and prints the sum of salaries.
Example Output:

yaml
Total Salary: 18000

5. Count the Number of Lines

Command:

bash
awk 'END {print NR}' employees.txt

Explanation:
Prints the total number of lines in the file.
Example Output:

3

6. Use Field Separator (CSV File)

Command:

bash
awk -F ',' '{print $1, $3}' employees.csv

Explanation:
Uses a comma , as the field separator.

Example (employees.csv):

1,John,5000
2,Alice,6000
3,Bob,7000

Output:

yaml
1 5000
2 6000
3 7000

7. Replace a Column Value

Command:

bash
awk '{$2="David"; print}' employees.txt

Explanation:
Replaces the second column with “David”.

8. Print Only Even Rows

Command:

bash
awk 'NR%2==0' employees.txt

Explanation:
Prints only even-numbered lines.

9. Find the Maximum Salary

Command:

bash
awk 'max < $3 {max=$3} END {print "Max Salary:", max}' employees.txt

Explanation:
Finds the highest salary in the third column.

10. AWK in a Pipeline

Command:

bash
ls -l | awk '{print $9, $5}'

Explanation:
Lists file names and their sizes.

These are just some basic examples. AWK is very powerful for text processing, and you can use it to manipulate, filter, and analyze text files efficiently.