gawk command in Linux with Examples

The gawk command in Linux is a pattern scanning and processing language. No compilation is required, and variables can be used along with numeric functions, string functions, and logical operators.

Gawk is a utility that enables programmers to write highly compact but still effective programs as statements that define text patterns to look for in a text document, and the action to be taken every time such a match is found within a line.

Gawk can be used to:

• Scan a file line by line
• Split each input line into fields
• Compare input line/fields to pattern
• Perform action(s) on matched lines
• Transform data files
• Produce formatted reports
• Format output lines
• Perform arithmetic and string operations
• Execute conditionals and loops

Syntax

gawk [POSIX / GNU style options] -f progfile [--] file ...
gawk [POSIX / GNU style options] [--] 'program' file ...

Basic gawk Command Example

By default, gawk prints every line of data from the named file:

gawk '{ print }' mobile.txt

Basic Options and Usage

Examples of Option Usage

Specifying field separator using -F option:

gawk -F: '{ print $1 }' /etc/passwd

Using -f option to read program from a file:

gawk -F: -f mobile.txt /etc/passwd

Built-In Variables

• NR: Keeps a running count of the number of input lines
• NF: Keeps a count of the number of fields in the current input record
• FS: Holds the field separator character
• RS: It saves the record separator character at the present time
• OFS: It saves the output field separator
• ORS: It saves the output record separator

Example using NR:

gawk '{ print NR "-" $1 }' mobile.txt

Advanced Usage Examples

Assume that we have a dataset in a file named mobile.txt:

Name    Mobile      Email
John    1234567890  [email protected]
Sunil   9876543210  [email protected]
Alice   5555555555  [email protected]

1. Print lines matching a pattern:

gawk '/Sunil/ ' mobile.txt

2. Print specific fields:

gawk '{ print $2 }' mobile.txt

3. Count the number of lines in a file:

gawk 'END  NR}' mobile.txt

Conclusion

The gawk command is actually one of the most powerful tools in Linux when it comes to text processing. The tool can scan files, process patterns, and execute many actions; it is very valuable to both system administrators and programmers. Mastering gawk will allow users to easily manipulate text data, generate reports, or automatically automate many other text-processing activities.