How to Split Text Using Regex in Golang?

What is regex? Is Regex the famous anime character? Oops, if you think so, you’re likely to be disappointed. The Go programming language uses the term regexp to denote Regular expressions. Regular expressions are very important in the field of string processing. The “regexp” package in Go holds all necessary pre-built functions that implement regular expression search and also guarantee a linear-time search in the size of the provided inputs. To know more about what regex is, read What is Regexp in Golang?

How to split input text using regexp (or regex)?

Regexp package contains the Split function which helps in splitting the input text string. Before we jump into the depths of regexp split function, let us brief you over some basic regular expressions that are worth remembering while using the split function:

Character(s)	What it signifies?	Example syntax	Result of regex
[ ]	[ ] Can be used for including or  excluding a given range, or even  mention specifically the characters  that we want to include or exclude.  [ ] means both inclusive in a range.	“[b-f]an”	ban, can, dan, ean, fan
{ }	The curly brackets are used when  one needs to match the frequency  of the occurrence of any given   expression.	“gf{1,}g”	gfg, gffg, gfffg,…
( )	( ) Can be used for including or  excluding a given range, or even  mention specifically the  characters that we want to  include or exclude. ( ) means  numbered capturing group.	“(b-f)an”	ban, can, dan, ean, fan
*	* Matches 0/0+ occurrences  of the character that precedes  the star (‘*’).	“gee*k”	gek, geek, geeek…
+	+ Matches 1/1+ occurrences  of the character that precedes  the plus (‘+’).	“gee+k”	geek, geeek,…
?	? Matches 0 & 1 occurrences  of the character that precedes  the question mark (‘?’).	“gee?k”	gek, geek
.	Anything can replace the dot  character, except a newline (\n).	“g.g”	gfg, gbg, gcg,…
^	Any text that starts with the string  mentioned after ‘^’.  Also used as a negation in groups  or other regular expressions (NOT).	“^ge” “[^0-8]*”	ge, geek, geeks,… ‘ ‘,9, 99,999,…
$	It denotes the end of the string in a   single-lined text and the end of a  line in a multi-line text.	“$de”	code, decode,…
|	| is the or operator.	“geek|principle”	geek, geeks, principle, principles..
\	This is the escape character  If you need to mention anything  like ‘\s’ then you need to  use ‘ \\s’ so that the system  understands that it is ‘\s’.	“\A” “\\n” “\\s”  etc..
\s	Extracts all white spaces only	“\\s”	” “, ”  “, ”   “,…
\S	Extracts all text except white spaces	“\\S”
\d	Extracts all digits only	“\\d”	0, 1, 2, 3, 4, 5, 6, 7, 8, 9
\D	Extracts all text except digits	“\\D”

Syntax:

func Split(s: string, n: int) []string

This function accepts a string and an integer and returns a slice of all substrings. The input string ‘s‘ is the string that will be further, split into substrings as per the given regular expression by Split function. ‘n‘ denotes the value that decides the number of substrings to be returned. 

• If n > 0: It means that a maximum of n substrings undergo the regex operation and will be returned.
• If n = 1 then no regex the operation will be performed and hence, the original string will be returned.
• If n = 0: It means that no substrings will be returned, a nill shall be returned.
• If n < 0: It means that all the substrings  that was created will be returned by the function.

Example 1:

Go

package main

import (
    f "fmt"
    re "regexp"
    // we import the regexp package
    // as re
)

// SPLIT function hacks
// In layman terms, whenever the
// string (given to split as argument)
// occurs, the string is split into
// a substring.

func main() {

    // str stores a sample string as shown below
    str := "I am at GFG!\nYou can call me at 9087651234."

    // just printing the original string: str
    f.Println(str)

    // We shall consider two scenarios
    // in this example code

    // Scenario 1:
    // Store a regex object that
    // contains digits only
    // in obj1.
    obj1 := re.MustCompile("\\d*")

    // Scenario 2:
    // Store a regex object that
    // contains everything except digits
    // in obj2.
    obj2 := re.MustCompile("\\D*")

    // Using obj1 as reference, we
    // are splitting the string: str
    // and -1 denotes that all substrings
    // ever created will be included.
    first := obj1.Split(str, -1)

    // "first" holds all the substrings
    // split from str w.r.t obj1 in a container
    // A container like, say a list.

    // Using obj2 as reference, we
    // are splitting the string: str
    // and -1 denotes that all substrings
    // ever created will be included.
    second := obj2.Split(str, -1)
    // "second" holds all the substrings
    // split from str w.r.t obj2 in a container
    // A container like, say a list.

    f.Println("Now printing text split by obj1...")
    for _, p := range first {
        f.Println(p)
    }

    f.Println("Now printing text split by obj2...")
    for _, q := range second {
        f.Println(q)
    }
}

Command to Execute:

> go run (your_file_name).go

Output:

I am at GFG!
You can call me at 9087651234.
Now printing text split by obj1...
I

a
m

a
t

G
F
G
!


Y
o
u

c
a
n

c
a
l
l

m
e

a
t

.
Now printing text split by obj2...

9
0
8
7
6
5
1
2
3
4

Visual I/O demo on Visual Studio Code:

Code output on-screen upon running the above-written code.

Example 2:

Go

package main

import (
    f "fmt"
    re "regexp"
)

// Simple example code to understand
// 1. Function of Split function
// 2. Parameters of split function
// regex-object.Split(string: , n: )

func main() {

    // Sample string that will be used in this
    // example "GeeksforGeeks loves bananas"
    str := "GeeksforGeeks loves bananas"
    f.Println(str)

    f.Println("Part-1: Excluding all vowels from given string")

    // a regexp object (geek) for storing all vowels
    geek := re.MustCompile("[aeiou]")
    f.Print("Printing all substring lists = ")

    // Checking split for n = -1
    f.Println(geek.Split(str, -1))
    f.Print("For n = 0 substring list = ")

    // Checking split for n = 0
    f.Println(geek.Split(str, 0))
    f.Print("For n = 1 substring list = ")

    // Checking split for n = 1
    f.Println(geek.Split(str, 1))
    f.Print("For n = 10 substring list = ")

    // Checking split for n = 10
    f.Println(geek.Split(str, 10))
    f.Print("For n = 100 substring list = ")

    // Checking split for n = 100
    f.Println(geek.Split(str, 100))

    f.Println("\n\nPart-2: Extracting all vowels from given string")

    // a regexp object (geek) for storing all consonants
    geek = re.MustCompile("[^aeiou]")

    f.Print("Printing all substring lists = ")

    // Checking split for n = -1
    f.Println(geek.Split(str, -1))
    f.Print("For n = 0 substring list = ")

    // Checking split for n = 0
    f.Println(geek.Split(str, 0))
    f.Print("For n = 1 substring list = ")

    // Checking split for n = 1
    f.Println(geek.Split(str, 1))
    f.Print("For n = 10 substring list = ")

    // Checking split for n = 10
    f.Println(geek.Split(str, 10))
    f.Print("For n = 100 substring list = ")

    // Checking split for n = 100
    f.Println(geek.Split(str, 100))

    // Did you notice that split function
    // does not modify the original regex
    // matching object?
}

Command to Execute:

> go run (your_file_name).go

Output:

GeeksforGeeks loves bananas
Part-1: Excluding all vowels from given string
Printing all substring lists = [G  ksf rG  ks l v s b n n s]
For n = 0 substring list = []
For n = 1 substring list = [GeeksforGeeks loves bananas]
For n = 10 substring list = [G  ksf rG  ks l v s b n nas]
For n = 100 substring list = [G  ksf rG  ks l v s b n n s]


Part-2: Extracting all vowels from given string
Printing all substring lists = [ ee   o  ee    o e   a a a ]
For n = 0 substring list = []
For n = 1 substring list = [GeeksforGeeks loves bananas]
For n = 10 substring list = [ ee   o  ee   loves bananas]
For n = 100 substring list = [ ee   o  ee    o e   a a a ]

Visual I/O demo on Visual Studio Code:

Code output on-screen upon running the above-written code.