Golang Regex: Match number or numeric digits in Regular Expression

Overview

\d can be used to match digits in golang. In fact, \d can be used to match the entire range.

0-9

The regular expression for matching any digit will be

\d

In case you want to match only a particular digit, let’s say 5 then the regular expression will be that digit.

5

If you want to match two digits then below will be the regex

\d\d

Match a single digit

Let’s see an example

package main

import (
	"fmt"
	"regexp"
)

func main() {
	sampleRegexp := regexp.MustCompile(`\d`)

	fmt.Println("For regex \\d")
	match := sampleRegexp.MatchString("1")
	fmt.Printf("For 1: %t\n", match)

	match = sampleRegexp.MatchString("4")
	fmt.Printf("For 4: %t\n", match)

	match = sampleRegexp.MatchString("9")
	fmt.Printf("For 9: %t\n", match)

	match = sampleRegexp.MatchString("a")
	fmt.Printf("For a: %t\n", match)

	sampleRegexp = regexp.MustCompile(`5`)
	fmt.Println("\nFor regex 5")
	match = sampleRegexp.MatchString("5")
	fmt.Printf("For 5: %t\n", match)

	match = sampleRegexp.MatchString("6")
	fmt.Printf("For 6: %t\n", match)
}

Output

For regex \d
For 1: true
For 4: true
For 9: true
For a: false

For regex 5
For 5: true
For 6: false

In the above program, we have examples of  two regexes

• \d – Match any digit

• 5  – Match only five

The first matches any single digit. That is why it matches

1
4
9

And it doesn’t match

a

The same is also evident from the output

The second regex matches only “5” and it doesn’t match “6” as is evident from the output

For regex 5
For 5: true
For 6: false

Match Repetition of digit

Quantifiers can be used to match the repetition of digits. Example

• \d+ – Match one or more digits

• \d* – Match zero or more digits

• \d{N} – Match N number of digits

package main

import (
	"fmt"
	"regexp"
)

func main() {
	sampleRegexp := regexp.MustCompile(`\d+`)

	fmt.Println(`For regex \d+`)
	match := sampleRegexp.MatchString("12345")
	fmt.Printf("For 12345: %t\n", match)

	match = sampleRegexp.MatchString("")
	fmt.Printf("For empty string: %t\n", match)

	sampleRegexp = regexp.MustCompile(`\d*`)

	fmt.Println()
	fmt.Println(`For regex \d*`)
	match = sampleRegexp.MatchString("12345")
	fmt.Printf("For 12345: %t\n", match)

	match = sampleRegexp.MatchString("")
	fmt.Printf("For empty string: %t\n", match)

	sampleRegexp = regexp.MustCompile(`\d{2}`)

	fmt.Println()
	fmt.Println(`For regex \d{2}`)
	match = sampleRegexp.MatchString("12")
	fmt.Printf("For 12: %t\n", match)

	match = sampleRegexp.MatchString("1")
	fmt.Printf("For 1: %t\n", match)
}

Output

For regex \d+
For 12345: true
For empty string: false

For regex \d*
For 12345: true
For empty string: true

For regex \d{2}
For 12: true
For 1: false

In the above program, we have examples of  three regexes

• \d+

• \d*

• \d{N}

\d+ regex gives a match for “12345” but fails for an empty string

\d*  gives a match for “12345” as well as an empty string

\d{2} matches a sequence of two digits. That is why it matches for “12” for fails for “1”

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