How to Read a CSV File in Golang?

Golang offers a vast inbuilt library that can be used to perform read and write operations on files. To read a CSV file, the following methods are used in Golang:

• os.Open(): The os.Open() method opens the named file for reading. This method returns either the os.File pointer or an error.  
• encoding/csv: This package provides a NewReader function which is used to read a CSV file and it returns a *csv.Reader which is further used to read the contents of the file as a series of records.

Note: Use the offline compiler for better results. Save the program file with .go  extension. Use the below command to execute the program:

go run filename.go

Example 1: Let us consider the CSV file named Students.csv and the contents inside the file are as follows:

S001,Thomas Hardy,CS01

S002,Christina Berglund,CS05

S003,Yang Wang,CS01

S004,Aria Cruz,CS05

S005,Hanna Moos,CS01

Below is the Golang program to read a CSV file:

Go

// Go program to illustrate
// How to read a csv file
package main

import (
    "encoding/csv"
    "fmt"
    "log"
    "os"
)

func main() {

    // os.Open() opens specific file in
    // read-only mode and this return
    // a pointer of type os.File
    file, err := os.Open("Students.csv")

    // Checks for the error
    if err != nil {
        log.Fatal("Error while reading the file", err)
    }

    // Closes the file
    defer file.Close()

    // The csv.NewReader() function is called in
    // which the object os.File passed as its parameter
    // and this creates a new csv.Reader that reads
    // from the file
    reader := csv.NewReader(file)

    // ReadAll reads all the records from the CSV file
    // and Returns them as slice of slices of string
    // and an error if any
    records, err := reader.ReadAll()

    // Checks for the error
    if err != nil
    {
        fmt.Println("Error reading records")
    }

    // Loop to iterate through
    // and print each of the string slice
    for _, eachrecord := range records
    {
        fmt.Println(eachrecord)
    }
}

Output:

Fig 1.1

One can also provide a custom separator to read CSV files instead of a comma(,), by defining that in Reader struct. 

Reader structure returned by NewReader function

type Reader struct{

// Comma is field delimiter set to (,) by NewReader

// which can be changed to custom delimeter 

// but it must be a valid rune and it should

// not be \r,\n or unicode replacement character (0xFFFD).

Comma rune

Comment rune

FieldsPerRecord int

LazyQuotes bool

TrimLeadingSpace bool

ReuseRecord bool

TrailingComma bool

}

 Example 2: Below example shows how to read a CSV file that has a custom separator. Let the CSV file be named Sample.csv and the contents in the file are as follows:

Word1-Word2

Word3-Word4

Word5-Word6

Below is the Golang program to read a CSV file with a custom separator:

Go

// Golang program to illustrate
// How to read a csv file with
// custom separator
package main

import (
    "encoding/csv"
    "fmt"
    "log"
    "os"
)

func main() {

    // os.Open() opens specific file in
    // read-only mode and this return
    // a pointer of type os.File
    file, err := os.Open("Sample.csv")

    // Checks for the error
    if err != nil {
        log.Fatal("Error while reading the file", err)
    }

    // Closes the file
    defer file.Close()

    // The csv.NewReader() function is called in
    // which the object os.File passed as its parameter
    // and this creates a new csv.Reader that reads
    // from the file
    reader := csv.NewReader(file)

    // To specify the custom separator use the
    // following syntax
    // Comma is the field delimiter. By default it is
    // set to comma (',') by NewReader.
    // Comma must be a valid rune (int32) and must not be
    // \r, \n, or the Unicode replacement character (0xFFFD).
    reader.Comma = '-'

    // ReadAll reads all the records from the CSV file and
    // Returns them as slice of slices of string and an
    // error if any
    records, err := reader.ReadAll()

    // Checks for the error
    if err != nil
    {
        fmt.Println("Error reading records")
    }

    // Loop to iterate through
    // and print each of the string slice
    for _, eachrecord := range records
    {
        fmt.Println(eachrecord)
    }

}

Output:

Fig 1.2