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Introduction
Regex stands for a regular expression that is made up of a special sequence of characters that defines a search pattern which is used for matching specific text and for more advanced text manipulation. A built-in package called “regexp” is present in the Golang for such regular expressions, it contains a list of actions like replacing, validating, extracting, etc. The regexp package uses RE2 syntax standards. Some of the commonly used functions are :
MatchString
This function is used to check whether the string passed as a parameter contains any match of the regular expression pattern or not. The function returns a boolean value and an error, if any.
Syntax
func MatchString(pattern string, s string)
Example
package main
import (
"fmt"
// import package
"regexp"
)
func main() {
// string in which the pattern is to be searched
str1 := "CodingNinjas"
// 1.returns true if the pattern is present
// in the string
match1, err := regexp.MatchString("Coding", str1)
fmt.Println("Match Found:", match1, " Error: ", err)
// 2.returns false as the pattern is not present
// in the string
match2, err := regexp.MatchString("World", str1)
fmt.Println("Match Found:", match2, " Error: ", err)
// throws an error
// as the pattern is not valid
match3, err := regexp.MatchString("Hel(lo", str1)
fmt.Println("Match Found:", match3, " Error: ", err)
}
Output
Match Found: true Error: <nil>
Match Found: false Error: <nil>
Match Found: false Error: error parsing regexp: missing closing ): `Hel(lo`
Compile
In order to store complicated regular expressions Compile() function is used. It parses a regular expression and returns a regexp object, if successful, which can be used to match against the text.
Syntax
func Compile(expression string)
Example
package main
import (
"fmt"
"log"
"regexp"
)
func main() {
words := [...]string{"Seven", "five", "twelve", "eleven"}
// can be reused later
re, err := regexp.Compile(".eve")
//check if error
if err != nil {
log.Fatal(err)
}
// check with every string
for _, word := range words {
found := re.MatchString(word)
if found {
fmt.Printf("%s matches\n", word)
} else {
fmt.Printf("%s does not match\n", word)
}
}
}
Output
Seven matches
five does not match
twelve does not match
eleven matches
FindAllString
This function is used to return a slice of all successive matches of the regular expression.
Example
package main
import (
"fmt"
"os"
"regexp"
)
func main() {
var message = `Boxes are cuboids. A box can be made of cardboard or any solid material. A box has 6 faces.`
re := regexp.MustCompile("(?i)box(es)?")
found := re.FindAllString(message, -1)
if found == nil {
fmt.Printf("no match found\n")
os.Exit(1)
}
fmt.Printf("Matches found are : \n")
for _, word := range found {
fmt.Printf("%s \n", word)
}
}
Output
Matches found are :
Boxes
box
box
FindAllStringIndex
This function is used to return the first and last index of a slice of all successive matches of the regular expression.
Example
package main
import (
"fmt"
"regexp"
)
func main() {
var message = `Boxes are cuboids. A box can be made of cardboard or any solid material. A box has 6 faces.`
re := regexp.MustCompile("(?i)box(es)?")
ind := re.FindAllStringIndex(message, -1)
for _, i := range ind {
match := message[i[0]:i[1]] // get the slice
fmt.Printf("%s at %d:%d\n", match, i[0], i[1])
}
}
Output
Boxes at 0:5
box at 21:24
box at 75:78
ReplaceAllStringFunc
This function is used to return a copy of a string in which all the matches of the regular expression have been replaced by the return value of that function.
This function is used to get substrings from a string, separated by the defined regular expression.
Example
package main
import (
"fmt"
"log"
"regexp"
"strconv"
)
func main() {
var data = `1, 2, 3, 4, 5, 6, 7, 8, 9, 10`
sum := 0
re := regexp.MustCompile(",\\s*")
nums := re.Split(data, -1)
for _, num := range nums {
n, err := strconv.Atoi(num) // convert string into integer
sum += n // add it to sum
if err != nil {
log.Fatal(err)
}
}
fmt.Println("The sum of values is",sum)
}
Output
The sum of values is 55
Few More Example
FAQs
What are the uses of using the regex package? The regexp package in Golang is used for various actions like filtering, replacing, validating, or extracting.
What is MustCompile in Golang? The MustCompile method compiles the regular expression and returns its instance. But It will cause an error if the pattern is invalid.
What should be passed as the second argument to the Split function to get the maximum number of substrings? The value which should be passed as the second argument to the Split function to get the maximum number of substrings is -1.
Key Takeaways
In this article, we have extensively discussed what regex is, what different functions are available in the regex package in Golang with examples and their implementation in Visual Studio Code.
We hope that this blog has helped you enhance your knowledge regarding regex in the Golang programming language and if you would like to learn more, check out our articles on what golang is, why it is popular among engineers, understanding the dynamic of Golang.
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