AWK Cheat Sheet

What is AWK?

awk is a powerful text-processing tool in Linux used to manipulate and analyze text files by processing patterns and performing actions.

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Basic Syntax

awk 'pattern {action}' file

• pattern: The condition to match (optional).
• action: Commands to execute on matching lines (optional).
• file: The file to process.

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Common Examples

1. Print All Lines

awk '{print}' file.txt

• Outputs all lines in file.txt.

2. Print Specific Columns

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

• Prints the 1st and 3rd columns.

3. Match a Pattern

awk '/error/ {print}' log.txt

• Prints lines containing the word error.

4. Conditional Filtering

awk '$3 > 100 {print $1, $3}' data.txt

• Prints rows where the 3rd column is greater than 100.

5. Add or Modify Columns

awk '{print $1, $2, $2 + $3}' data.txt

• Adds a column with the sum of the 2nd and 3rd columns.

6. Count Matching Lines

awk '/pattern/ {count++} END {print count}' file.txt

• Counts and prints lines matching pattern.

7. Format Output

awk '{printf "Name: %s, Age: %d\n", $1, $2}' names.txt

• Formats and prints fields with a custom output.

8. Use Field Separator

awk -F ':' '{print $1, $NF}' /etc/passwd

• Uses : as a separator and prints the 1st and last columns.

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Key Concepts

Symbol	Meaning
$1, $2	Represents the 1st, 2nd columns (fields).
NR	Line number (e.g., NR == 5 matches line 5).
NF	Total number of fields in a line.
FS	Field Separator (-F or FS=",").
BEGIN	Executes before processing lines.
END	Executes after processing all lines.

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Advanced Examples

Print Line Numbers

awk '{print NR, $0}' file.txt

• Prints line numbers alongside the content.

Find Maximum in a Column

awk '$3 > max {max = $3} END {print max}' data.txt

• Finds and prints the maximum value in the 3rd column.

Sum a Column

awk '{sum += $3} END {print sum}' data.txt

• Sums up all values in the 3rd column.

Filter by Field Count

awk 'NF == 3 {print}' file.txt

• Prints lines with exactly 3 fields.

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Practice Data

Create a sample.txt to test commands:

John 25 500
Mary 30 600
Alex 28 450

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Tips

• Test commands with awk on small files before applying to large ones.
• Combine with other commands like grep or sed for complex workflows.