Golang Regex: Case insensitive regular expression matching in Go (Golang)

Overview

The default behavior for regular expression matching in golang is case sensitive. But the default behavior can be changed by adding a set of flags to the beginning of the regular expression. The flag we need to add to the beginning of regex is:

(?i)

The flag ‘i’ is used to indicate that the regex will be case insensitive.

Here is the example regex for case sensitive and insensitive regex.

Case sensitive regex

abc

Case insensitive regex

(?i)abc

Program

Let’s see a program for the same.

package main

import (
	"fmt"
	"regexp"
)

func main() {
	sampleRegex := regexp.MustCompile("(?i)abc")

	match := sampleRegex.Match([]byte("abc"))
	fmt.Printf("For abc: %t\n", match)

	match = sampleRegex.Match([]byte("ABC"))
	fmt.Printf("For ABC: %t\n", match)
}

Output

For abc: true
For ABC: true

Notice the regex in the above program. We prefixed the regex with (?i) flag to indicate that this regex will be case insensitive

(?i)abc

As we can notice from the output, it gives a correct match for text “abc” as well as text “ABC”.

If we remove the prefix flag then it will  give a false match for “ABC”

package main

import (
	"fmt"
	"regexp"
)

func main() {
	sampleRegex := regexp.MustCompile("abc")

	match := sampleRegex.Match([]byte("abc"))
	fmt.Printf("For abc: %t\n", match)

	match = sampleRegex.Match([]byte("ABC"))
	fmt.Printf("For ABC: %t\n", match)
}

Output

For abc: true
For ABC: false

Notice the regex in the above program. We do not prefix the regex with (?i) flag. So it will fall back to the default behavior of being case sensitive.

abc

As we can notice from the output, it gives a correct match for text “abc” but it does not give a match for text “ABC”.

This is all about case insensitive regex matching in golang. Hope you have liked this article.

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