AWK tutorial: awk regex example

Linux awk command has great advantages in text processing, which contains regular expression processing.

Usually I use the linux grep command to filter and filter text.

Today, I will introduce to you how to use the awk regular command for text filtering and processing.

Before the formal introduction, first spread a few concepts to everyone:

What Is Regex?

Usually, regular expressions or regex are the text patterns you define.

Types of Regex

Linux has two regular expression engines:

• BRE: The Basic Regular Expression engine.
• ERE: The Extended Regular Expression engine.

Compared to the BRE engine, the ERE engine comes with some programming languages ​​that provides more patterns.

Awk using BRE regex Patterns

➜  awk '/linux-tutorial/{print $0}' ../log/www.linuxcommands.site_nginx.log | head -3

Special Characters

.*[]^${}\+?|()

Sometimes you will encounter situations where special characters are handled, for example:

➜ awk -F' ' '{print $11}' ../log/www.linuxcommands.site_nginx.log | awk '/\?/{print $0}' | head -5

You need to escape these special characters using the backslash character (\).

Awk using ERE regex Patterns

➜ awk -F' ' '{print $7}' ../log/www.linuxcommands.site_nginx.log | awk '/amp\/$/{print $0}' | head -5

The caret character (^) matches the start of text:

➜ awk -F' ' '{print $7}' ../log/www.linuxcommands.site_nginx.log | awk '/^\/robot/{print $0}' | head -5

The character class is defined using square brackets [] like this:

➜ awk '/[h|e]re/{print $0}' test-3.txt

Ranges

➜ awk -F' ' '{print $7}' ../log/www.linuxcommands.site_nginx.log | awk '/[0-9]$/{print $0}' | head -5