Input and Output in Go (Detailed Explanation)

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March 6, 2025
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6 min read

In the Go programming language, input and output (I/O) operations are performed using the fmt, bufio, and os packages.

🔹 1ī¸âƒŖ Output in Go

Go provides multiple ways to display output using the fmt package.

✅ fmt.Print(), fmt.Println(), and fmt.Printf()

FunctionDescription
fmt.Print()Prints text without a newline
fmt.Println()Prints text and adds a newline (\n) at the end
fmt.Printf()Prints formatted output

📝 Example:

Go
package main

import "fmt"

func main() {
    name := "Go"
    version := 1.21

    fmt.Print("Hello, ")  
    fmt.Print("World!\n")  

    fmt.Println("This is Golang")  
    fmt.Println("Version:", version)  

    fmt.Printf("Hello %s! Your version is %.2f\n", name, version)  
}

🔹 Output:

Hello, World!
This is Golang
Version: 1.21
Hello Go! Your version is 1.21

🔹 2ī¸âƒŖ Input in Go

Go provides multiple ways to take user input using fmt.Scan(), fmt.Scanln(), fmt.Scanf(), and the bufio package.

✅ fmt.Scan()

👉 Accepts multiple inputs, separated by spaces.

Go
package main

import "fmt"

func main() {
    var name string
    var age int

    fmt.Print("Enter your name and age: ")
    fmt.Scan(&name, &age)  // Input must be space-separated

    fmt.Println("Name:", name)
    fmt.Println("Age:", age)
}

🔹 Input:

John 30

🔹 Output:

Name: John
Age: 30

✅ fmt.Scanln()

👉 fmt.Scanln() reads multiple inputs but stops at a newline.

Go
package main

import "fmt"

func main() {
    var name string

    fmt.Print("Enter your name: ")
    fmt.Scanln(&name)  

    fmt.Println("Welcome,", name)
}

🔹 Input:

Alice

🔹 Output:

Welcome, Alice

✅ fmt.Scanf() (Formatted Input)

👉 fmt.Scanf() allows formatted input.

Go
package main

import "fmt"

func main() {
    var name string
    var age int

    fmt.Print("Enter your name and age: ")
    fmt.Scanf("%s %d", &name, &age)  

    fmt.Printf("Hello %s, you are %d years old.\n", name, age)
}

🔹 Input:

Alice 25

🔹 Output:

Hello Alice, you are 25 years old.

🔹 3ī¸âƒŖ Using bufio and os for Input

👉 bufio.NewReader() is used for reading full-line input, including spaces.

✅ Using bufio.NewReader()

Go
package main

import (
    "bufio"
    "fmt"
    "os"
)

func main() {
    reader := bufio.NewReader(os.Stdin)

    fmt.Print("Enter your full name: ")
    name, _ := reader.ReadString('\n')  // Reads input until a newline

    fmt.Println("Welcome,", name)
}

🔹 Input:

John Doe

🔹 Output:

Welcome, John Doe

👉 This method is better than fmt.Scanln() because it allows reading entire lines with spaces.

🔹 4ī¸âƒŖ File Input and Output (File I/O)

👉 The os and ioutil packages allow reading and writing files.

✅ Reading from a file (os.ReadFile)

Go
package main

import (
    "fmt"
    "os"
)

func main() {
    data, err := os.ReadFile("sample.txt")
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("File Content:")
    fmt.Println(string(data))
}

✅ Writing to a file (os.WriteFile)

Go
package main

import (
    "fmt"
    "os"
)

func main() {
    content := []byte("Hello, this is a test file!")

    err := os.WriteFile("output.txt", content, 0644)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("File written successfully!")
}

🔹 5ī¸âƒŖ String Input and Output

👉 Go provides functions for string handling using the strings package.

✅ Using fmt.Sprintf() for String Formatting

Go
package main

import (
    "fmt"
)

func main() {
    name := "Go"
    version := 1.21

    result := fmt.Sprintf("Language: %s, Version: %.2f", name, version)
    fmt.Println(result)
}

🔹 Output:

Language: Go, Version: 1.21

👉 fmt.Sprintf() allows formatted string output without printing it directly.

🔹 6ī¸âƒŖ Using the log Package (Debugging & Logging)

👉 log package is useful for debugging and logging errors.

✅ Using log.Println()

Go
package main

import (
    "log"
)

func main() {
    log.Println("This is a log message")
}

🔹 Output:

2025/02/15 12:34:56 This is a log message

🔹 7ī¸âƒŖ Summary Table

FunctionDescription
fmt.Print()Prints text in a single line
fmt.Println()Prints text and moves to a new line
fmt.Printf()Prints formatted output
fmt.Scan()Takes input (space-separated)
fmt.Scanln()Takes input until a newline
fmt.Scanf()Takes formatted input
bufio.NewReader(os.Stdin)Reads a full line of input
os.ReadFile()Reads data from a file
os.WriteFile()Writes data to a file
fmt.Sprintf()Formats a string without printing

Go āĻĒā§āĻ°ā§‹āĻ—ā§āĻ°āĻžāĻŽāĻŋāĻ‚ āĻ­āĻžāĻˇāĻžāĻ¯āĻŧ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ“ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ (āĻŦāĻŋāĻ¸ā§āĻ¤āĻžāĻ°āĻŋāĻ¤ āĻŦā§āĻ¯āĻžāĻ–ā§āĻ¯āĻž)

Go (Golang) āĻĒā§āĻ°ā§‹āĻ—ā§āĻ°āĻžāĻŽāĻŋāĻ‚ āĻ­āĻžāĻˇāĻžāĻ¯āĻŧ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ“ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ (I/O) āĻĒāĻ°āĻŋāĻšāĻžāĻ˛āĻ¨āĻž āĻ•āĻ°āĻ¤ā§‡ fmt, bufio, āĻāĻŦāĻ‚ os āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻšāĻ¯āĻŧāĨ¤

🔹 1ī¸âƒŖ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ (Output)

👉 Go-āĻ¤ā§‡ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ āĻĒā§āĻ°āĻĻāĻžāĻ¨ā§‡āĻ° āĻœāĻ¨ā§āĻ¯ āĻŽā§‚āĻ˛āĻ¤ fmt āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻšāĻ¯āĻŧāĨ¤

✅ fmt.Print(), fmt.Println(), āĻāĻŦāĻ‚ fmt.Printf()

āĻĢāĻžāĻ‚āĻļāĻ¨āĻŦā§ˆāĻļāĻŋāĻˇā§āĻŸā§āĻ¯
fmt.Print()āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ­āĻžāĻŦā§‡ āĻŸā§‡āĻ•ā§āĻ¸āĻŸ āĻĒā§āĻ°āĻŋāĻ¨ā§āĻŸ āĻ•āĻ°ā§‡, āĻ•ā§‹āĻ¨ā§‹ āĻ¨āĻ¤ā§āĻ¨ āĻ˛āĻžāĻ‡āĻ¨ āĻĻā§‡āĻ¯āĻŧ āĻ¨āĻž
fmt.Println()āĻŸā§‡āĻ•ā§āĻ¸āĻŸ āĻĒā§āĻ°āĻŋāĻ¨ā§āĻŸ āĻ•āĻ°ā§‡ āĻāĻŦāĻ‚ āĻļā§‡āĻˇā§‡ āĻ¨āĻ¤ā§āĻ¨ āĻ˛āĻžāĻ‡āĻ¨ (\n) āĻ¯ā§āĻ•ā§āĻ¤ āĻ•āĻ°ā§‡
fmt.Printf()āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸā§‡āĻĄ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ āĻĒā§āĻ°āĻŋāĻ¨ā§āĻŸ āĻ•āĻ°ā§‡

📝 āĻ‰āĻĻāĻžāĻšāĻ°āĻŖ:

Go
package main

import "fmt"

func main() {
    name := "Go"
    version := 1.21

    fmt.Print("Hello, ")  
    fmt.Print("World!\n")  

    fmt.Println("This is Golang")  
    fmt.Println("Version:", version)  

    fmt.Printf("Hello %s! Your version is %.2f\n", name, version)  
}

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Hello, World!
This is Golang
Version: 1.21
Hello Go! Your version is 1.21

🔹 2ī¸âƒŖ āĻ‡āĻ¨āĻĒā§āĻŸ (Input)

👉 Go-āĻ¤ā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻžāĻ° āĻœāĻ¨ā§āĻ¯ fmt.Scan(), fmt.Scanln(), fmt.Scanf(), āĻāĻŦāĻ‚ bufio āĻ“ os āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻšāĻ¯āĻŧāĨ¤

✅ fmt.Scan()

👉 āĻāĻ•āĻžāĻ§āĻŋāĻ• āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻž āĻ¯āĻžāĻ¯āĻŧ, āĻ¤āĻŦā§‡ āĻ¸ā§āĻĒā§‡āĻ¸ āĻĻāĻŋāĻ¯āĻŧā§‡ āĻĒā§ƒāĻĨāĻ• āĻ•āĻ°āĻ¤ā§‡ āĻšāĻ¯āĻŧāĨ¤

Go
package main

import "fmt"

func main() {
    var name string
    var age int

    fmt.Print("Enter your name and age: ")
    fmt.Scan(&name, &age)  // āĻ¸ā§āĻĒā§‡āĻ¸ āĻĻāĻŋāĻ¯āĻŧā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻĻāĻŋāĻ¤ā§‡ āĻšāĻŦā§‡

    fmt.Println("Name:", name)
    fmt.Println("Age:", age)
}

🔹 āĻ‡āĻ¨āĻĒā§āĻŸ:

John 30

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Name: John
Age: 30

✅ fmt.Scanln()

👉 fmt.Scanln() āĻāĻ•āĻžāĻ§āĻŋāĻ• āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ¯āĻŧ āĻ•āĻŋāĻ¨ā§āĻ¤ā§ āĻ¨āĻ¤ā§āĻ¨ āĻ˛āĻžāĻ‡āĻ¨ āĻĒāĻ°ā§āĻ¯āĻ¨ā§āĻ¤ āĻĒāĻĄāĻŧā§‡āĨ¤

Go
package main

import "fmt"

func main() {
    var name string

    fmt.Print("Enter your name: ")
    fmt.Scanln(&name)  

    fmt.Println("Welcome,", name)
}

🔹 āĻ‡āĻ¨āĻĒā§āĻŸ:

Alice

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Welcome, Alice

✅ fmt.Scanf() (āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸā§‡āĻĄ āĻ‡āĻ¨āĻĒā§āĻŸ)

👉 fmt.Scanf() āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻŸ āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

Go
package main

import "fmt"

func main() {
    var name string
    var age int

    fmt.Print("Enter your name and age: ")
    fmt.Scanf("%s %d", &name, &age)  

    fmt.Printf("Hello %s, you are %d years old.\n", name, age)
}

🔹 āĻ‡āĻ¨āĻĒā§āĻŸ:

Alice 25

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Hello Alice, you are 25 years old.

🔹 3ī¸âƒŖ bufio āĻāĻŦāĻ‚ os āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻĻāĻŋāĻ¯āĻŧā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻž

👉 bufio.NewReader() āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻ˛ā§‡ āĻ¸āĻŽā§āĻĒā§‚āĻ°ā§āĻŖ āĻ˛āĻžāĻ‡āĻ¨ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

✅ bufio.NewReader() āĻĻāĻŋāĻ¯āĻŧā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻž

Go
package main

import (
    "bufio"
    "fmt"
    "os"
)

func main() {
    reader := bufio.NewReader(os.Stdin)

    fmt.Print("Enter your full name: ")
    name, _ := reader.ReadString('\n')  // āĻ¨āĻ¤ā§āĻ¨ āĻ˛āĻžāĻ‡āĻ¨ āĻĒāĻ°ā§āĻ¯āĻ¨ā§āĻ¤ āĻĒāĻĄāĻŧā§‡

    fmt.Println("Welcome,", name)
}

🔹 āĻ‡āĻ¨āĻĒā§āĻŸ:

John Doe

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Welcome, John Doe

👉 āĻāĻŸāĻŋ fmt.Scanln()-āĻāĻ° āĻšā§‡āĻ¯āĻŧā§‡ āĻŦā§‡āĻļāĻŋ āĻ‰āĻĒāĻ¯ā§‹āĻ—ā§€ āĻ•āĻžāĻ°āĻŖ āĻāĻŸāĻŋ āĻ¸ā§āĻĒā§‡āĻ¸āĻ¸āĻš āĻ¸āĻŽā§āĻĒā§‚āĻ°ā§āĻŖ āĻ˛āĻžāĻ‡āĻ¨ āĻ—ā§āĻ°āĻšāĻŖ āĻ•āĻ°ā§‡āĨ¤

🔹 4ī¸âƒŖ āĻĢāĻžāĻ‡āĻ˛ āĻĨā§‡āĻ•ā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ“ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ (File I/O)

👉 Go-āĻ¤ā§‡ os āĻ“ ioutil āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡ āĻĢāĻžāĻ‡āĻ˛ āĻĨā§‡āĻ•ā§‡ āĻĄāĻžāĻŸāĻž āĻĒāĻĄāĻŧāĻž āĻ“ āĻ˛ā§‡āĻ–āĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

✅ āĻĢāĻžāĻ‡āĻ˛ āĻĨā§‡āĻ•ā§‡ āĻĄāĻžāĻŸāĻž āĻĒāĻĄāĻŧāĻž (os.ReadFile)

Go
package main

import (
    "fmt"
    "os"
)

func main() {
    data, err := os.ReadFile("sample.txt")
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("File Content:")
    fmt.Println(string(data))
}

✅ āĻĢāĻžāĻ‡āĻ˛ āĻ˛āĻŋāĻ–āĻž (os.WriteFile)

Go
package main

import (
    "fmt"
    "os"
)

func main() {
    content := []byte("Hello, this is a test file!")

    err := os.WriteFile("output.txt", content, 0644)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("File written successfully!")
}

🔹 5ī¸âƒŖ Go-āĻ¤ā§‡ āĻ¸ā§āĻŸā§āĻ°āĻŋāĻ‚ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ“ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ

👉 āĻ¸ā§āĻŸā§āĻ°āĻŋāĻ‚ āĻšā§āĻ¯āĻžāĻ¨ā§āĻĄāĻ˛āĻŋāĻ‚āĻ¯āĻŧā§‡āĻ° āĻœāĻ¨ā§āĻ¯ strings āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

✅ fmt.Sprintf() – āĻ¸ā§āĻŸā§āĻ°āĻŋāĻ‚ āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸāĻŋāĻ‚

Go
package main

import (
    "fmt"
)

func main() {
    name := "Go"
    version := 1.21

    result := fmt.Sprintf("Language: %s, Version: %.2f", name, version)
    fmt.Println(result)
}

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Language: Go, Version: 1.21

👉 fmt.Sprintf() āĻ¸ā§āĻŸā§āĻ°āĻŋāĻ‚ āĻ¤ā§ˆāĻ°āĻŋ āĻ•āĻ°āĻ¤ā§‡ āĻ¸āĻžāĻšāĻžāĻ¯ā§āĻ¯ āĻ•āĻ°ā§‡, āĻ¯ā§‡āĻ–āĻžāĻ¨ā§‡ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ āĻ¸āĻ°āĻžāĻ¸āĻ°āĻŋ āĻ¸ā§āĻŸā§āĻ°āĻŋāĻ‚āĻ¯āĻŧā§‡ āĻ¸āĻ‚āĻ°āĻ•ā§āĻˇāĻŖ āĻ•āĻ°āĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

🔹 6ī¸âƒŖ log āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° (Debugging & Logging)

👉 log āĻĒā§āĻ¯āĻžāĻ•ā§‡āĻœ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡ āĻāĻ°āĻ° āĻ˛āĻ— āĻ“ āĻĄāĻŋāĻŦāĻžāĻ—āĻŋāĻ‚ āĻ•āĻ°āĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

✅ log.Println() āĻ‰āĻĻāĻžāĻšāĻ°āĻŖ

Go
package main

import (
    "log"
)

func main() {
    log.Println("This is a log message")
}

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

2025/02/15 12:34:56 This is a log message

🔹 7ī¸âƒŖ āĻ¸āĻžāĻ°āĻ¸āĻ‚āĻ•ā§āĻˇā§‡āĻĒ (Summary)

āĻĢāĻžāĻ‚āĻļāĻ¨āĻŦā§āĻ¯āĻžāĻ–ā§āĻ¯āĻž
fmt.Print()āĻāĻ• āĻ˛āĻžāĻ‡āĻ¨ā§‡ āĻŸā§‡āĻ•ā§āĻ¸āĻŸ āĻĒā§āĻ°āĻŋāĻ¨ā§āĻŸ āĻ•āĻ°ā§‡
fmt.Println()āĻ¨āĻ¤ā§āĻ¨ āĻ˛āĻžāĻ‡āĻ¨ā§‡ āĻĒā§āĻ°āĻŋāĻ¨ā§āĻŸ āĻ•āĻ°ā§‡
fmt.Printf()āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸā§‡āĻĄ āĻ†āĻ‰āĻŸāĻĒā§āĻŸ
fmt.Scan()āĻ¸ā§āĻĒā§‡āĻ¸ āĻĻāĻŋāĻ¯āĻŧā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ āĻ¨ā§‡āĻ“āĻ¯āĻŧāĻž
fmt.Scanln()āĻ¨āĻ¤ā§āĻ¨ āĻ˛āĻžāĻ‡āĻ¨ āĻĒāĻ°ā§āĻ¯āĻ¨ā§āĻ¤ āĻ‡āĻ¨āĻĒā§āĻŸ
fmt.Scanf()āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻŸ āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸā§‡ āĻ‡āĻ¨āĻĒā§āĻŸ
bufio.NewReader(os.Stdin)āĻ¸āĻŽā§āĻĒā§‚āĻ°ā§āĻŖ āĻ˛āĻžāĻ‡āĻ¨ āĻ‡āĻ¨āĻĒā§āĻŸ āĻĒāĻĄāĻŧāĻ¤ā§‡ āĻĒāĻžāĻ°ā§‡
os.ReadFile()āĻĢāĻžāĻ‡āĻ˛ āĻĒāĻĄāĻŧāĻž
os.WriteFile()āĻĢāĻžāĻ‡āĻ˛ āĻ˛ā§‡āĻ–āĻž
fmt.Sprintf()āĻ¸ā§āĻŸā§āĻ°āĻŋāĻ‚ āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻŸāĻŋāĻ‚
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