AWK Command in Unix/Linux with Examples

What is AWK?

It is a scripting language and considered the most powerful command in the Linux environment. It does not require any compiling and generates reports by processing some files and then analyze those files. It is used to manipulate data and is thus suitable for pattern searching and processing.

What Operations Can AWK Perform?

• Scan files line by line.
• Splits input record into fields
• Compare the fields to patterns
• Perform on action matched pattern

How is AWK Command Useful in Linux and Unix?

• It helps in manipulating data files as per the user requirements.
• It generates formatted outputs.

What are the various Program Constructs that AWK Offers?

Various programming concepts offered by AWK are:

• Output formatting
• Inbuilt variables
• Pattern matching
• String operations
• Arithmetic operations

Basic Syntax of AWK Command

$ awk options 'selection _criteria ' input-file > output-file

Various AWK Commands

Consider the following data table in a sample text file called sample.txt

1. Printing the table line by line

$ awk ‘’    sample.txt

The command above prints each line of the file.

2. Printing table row-wise

$ awk ‘’ sample.txt
$ awk ‘’    sample.txt

The above code prints all the rows of the table.

3. Printing Columns

$ awk ‘’    sample.txt

The above code prints the first column of the table.

Similarly, we can print other columns of the table.

$ awk ‘’    sample.txt

Prints second column

$ awk ‘’    sample.txt

Prints third column

4. Printing Matched Pattern

Wrap the specific pattern to be matched within the forward-slash to print the lines that match the particular pattern. Syntax:

$ awk ‘’    sample.txt
$ awk '/variable_to_be_matched/ '   file.txt

Example: Print the data which contains Apple in its fields.

$ awk '/Apple/ '   sample.txt

The above command prints the following rows:

5. Inbuilt Variables

AWK offers certain inbuilt variables that help to manipulate and analyze data. Enlisted are a few inbuilt variables.

5.1. NR

The variable returns the rows with the current count of the number of input records.

$ awk ‘’ sample.txt

The above command counts the number of input records in the data. In this example, the table consists of a total of six records.

5.2. NF

The variable prints the count of fields for each record.

$ awk ‘’ sample.txt

The above command prints the last column of the table.

5.3. $NF

The variable returns the last column of the table

$ awk ‘’ sample.txt

Similarly, we can print the second last and third last column of the table.

$ awk ‘’ sample.txt

$ awk ‘’ sample.txt

5.4. ORS (Output Record Separator)

The variable separates every record in the desired output format.

$ awk ‘ BEGIN ’    sample.txt

Following output is printed:

ID  Name  Age  Company  Skill: 101  John  28  Apple  iOS:  102  Chris  33  NextDoor  Android: 103  Smith  45  Facebook Haskell:  104  Jack 33  Apple  Java: 105  May 27  Google  Python:

5.5. OFS

Output Field Separator The variable separates every field in the desired output format.

$ awk ‘ BEGIN ’    sample.txt
$ awk ‘ BEGIN ’    sample.txt

ID==Name
101==John
102==Chris
103==Smith
104==Jack
105==May

$ awk ‘ BEGIN ’    sample.txt

5.6. RS

It is the current record separator character. The default record separator character is the newline, since, by default, an input line is the input record.

RS$ awk ‘ BEGIN ’    sample.tx

6. IF Command

This command applies conditions on the data set and prints the data that satisfies the condition. Syntax:

$ awk ‘{ if(condition) } END  ’ file.txt

Example: Print the length of the longest line present in the file.

$ awk '{ if (length($0) > max) max = length($0) } END { print max }' sample.txt

7. String Operations

We can also do string operations on the file with AWK commands. Syntax:

$ awk ‘{ if(condition) print $0}’ sample.txt

Examples:

$ awk ‘{ if($1 == “John” ) print $0}’   sample.txt

The above code prints the rows with any field containing “John.”

$ awk ‘{ if($1 == “Apple” ) print $0}’   sample.txt

The above code prints the rows with any field containing “Apple.”

Linux Command Line, Bash Shell, Scripting AWK & SED on Linux

8. Length

The command counts the length of characters in each line. Example: Print the lines with more than ten characters

$ awk ‘length($0) > 24 ’   sample.txt

The command above prints the lines with a character length greater than 24.

9. Count

Counts the lines in the file

$ awk ‘END ’   sample.txt

Six is printed as there are six lines in the file. 6

10. For

Print the squares of first numbers from 1 to n. Let n = 5

$ awk 'BEGIN { for(i=1;i<=6;i++) print "square of", i, "is",i*i; }'

Output:

square of 1 is 1
square of 2 is 4
square of 3 is 9
square of 4 is 16
square of 5 is 25

11. Non-empty Line

$ awk ‘ NF > 0 ’ sample.txt Output: 0

12. Arithmetic Operations

AWK commands allow performing arithmetic operations if the table elements are numbers.

$ awk ‘ ’   sample.txt

Output:

13. Saving Output

Use the redirection operator “>” to save the output results. Results can be verified using the cat command.

$ cat output.txt

Conclusion

AWK command in Linux enable a programmer to write useful programs in the form of statements defining specific patterns to be searched for in each line of the file and the action which is to be taken when a match is found within a line. AWK command in Unix is used for pattern processing and scanning. It searches one or more files to see if they contain lines that match the specified patterns and then perform the associated actions.

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