Home » Golang » Golang Reference

Golang os.O_EXCL Constant with Examples

Golang | os.O_EXCL Constant: Here, we are going to learn about the O_EXCL constant of the os package with its usages, syntax, and examples.
Submitted by IncludeHelp, on October 23, 2021

os.O_EXCL

In the Go language, the os package provides a platform-independent interface to operating system (Unix-like) functionality. The O_EXCL constant is used to create a file if the file does not exist. It is used with the O_CREATE constant. Please note that the file must not exist.

The value of the O_EXCL constant is 128.

Syntax:

O_EXCL int

Implementation in the package source code:

const O_EXCL int = syscall.O_EXCL

Parameter(s):

• None

Return Value:

The return type of the os.O_EXCL constant is an int, it returns 128 i.e., the value of the O_EXCL constant is 128.

Example 1:

// Golang program to demonstrate the
// example of O_EXCL constant

package main

import (
	"fmt"
	"os"
)

func main() {
	// Printing the type and value
	fmt.Printf("Type of os.O_EXCL: %T\n",
		os.O_EXCL)
	fmt.Printf("Value of os.O_EXCL: %d\n",
		os.O_EXCL)
}

Output:

Type of os.O_EXCL: int
Value of os.O_EXCL: 128

Example 2:

// Golang program to demonstrate the
// example of O_EXCL constant

package main

import (
	"fmt"
	"os"
)

func main() {
	// Creating a file, file must not exist
	f, err := os.OpenFile("file.txt",
		os.O_CREATE|os.O_EXCL, 0755)
	fmt.Println(f, ",", err)
}

Output:

RUN 1: (If file exists)
<nil> , open file.txt: file exists

RUN 2: (RUN 1: (If file doesn't exist)
&{0xc000056180} , <nil>

Golang os Package »

---