Blank Identifier Imports in Go: What `_` Means in an Import Statement

By the end of this page, you will understand what a blank identifier import is in Go, why _ "package/path" is used, and how it allows a package to run its initialization code without directly referencing its exported names. You will also see why this pattern is common with database drivers, image decoders, and plugin-style registration systems.

In Go, an import like this:

_ "github.com/mattn/go-sqlite3"

is called a blank identifier import or side-effect import.

The underscore _ means:

• import the package
• do not bind it to a usable name in this file
• keep only the package's side effects

The most important side effect is that the package's init() functions run.

Why this matters

Some packages are not imported because you want to call their functions directly. Instead, you import them because they register themselves with another part of the program during initialization.

In your example:

_ "github.com/mattn/go-sqlite3"

go-sqlite3 registers itself as a SQL driver when the package is initialized. Then the database/sql package can use that driver later through calls such as:

sql.Open("sqlite3", "my.db")

Even though you never write something like sqlite3.SomeFunction(), the import is still necessary because the driver registration happens automatically inside the imported package.

Think of a blank import like plugging a device into a system without directly pressing any buttons on the device.

• A normal import is like hiring a worker and then giving them tasks directly.
• A blank import is like bringing in a technician who quietly sets up the system in the background.

You never speak to that technician in your code, but their setup work makes the rest of the program function.

For go-sqlite3, the package quietly says: "I am a SQLite driver; register me with database/sql." After that, database/sql knows how to open SQLite connections.

Core syntax

import _ "package/path"

This means:

• import the package
• execute its initialization code
• do not create a package name you can use in this file

Example: database driver

package main

import (
    "database/sql"
    "fmt"
    _ "github.com/mattn/go-sqlite3"
)

func main() {
    db, err := sql.Open("sqlite3", "example.db")
    if err != nil {
        fmt.Println("open error:", err)
        return
    }
    defer db.Close()

    fmt.Println("SQLite driver loaded successfully")
}

What is happening here?

• database/sql provides a generic database API.
• go-sqlite3 provides a concrete SQLite driver.
• The SQLite package registers itself in its init() function.
• sql.Open("sqlite3", ...) works because the driver was registered during import.

Consider this example:

package main

import (
    "database/sql"
    "fmt"
    _ "github.com/mattn/go-sqlite3"
)

func main() {
    db, err := sql.Open("sqlite3", "test.db")
    if err != nil {
        fmt.Println(err)
        return
    }
    defer db.Close()

    fmt.Println("connected")
}

Step-by-step

1. The program starts

Go loads imported packages before running main().

2. github.com/mattn/go-sqlite3 is imported

Even though it is imported with _, Go still loads the package.

3. The package's init() function runs

Inside the SQLite driver package, an init() function registers the driver with database/sql.

Conceptually, it does something like this:

1. Database drivers

This is the most common example.

import (
    "database/sql"
    _ "github.com/lib/pq"
)

Used when:

• connecting to PostgreSQL, MySQL, SQLite, or SQL Server
• keeping application code written against database/sql
• swapping drivers without changing most business logic

2. Image format support

import (
    "image"
    _ "image/gif"
    _ "image/jpeg"
    _ "image/png"
)

Used when:

• reading uploaded images
• processing files in scripts
• supporting multiple formats through one API

3. Plugin-style registration

A package may register:

• commands
• file parsers
• serializers
• metrics exporters
• authentication providers

This is useful when a main application discovers available functionality through a registry rather than hardcoded function calls.

4. Monitoring and instrumentation

Some libraries install tracing, metrics, or hooks during initialization. A blank import can activate them if the package is designed that way.

5. Testing helpers

In real Go projects, blank imports are usually used deliberately and sparingly.

Common pattern: registry-based architecture

A package exposes a generic API and a registration mechanism. Another package imports implementations only for their registration side effects.

Examples:

• database/sql + database driver packages
• image + format decoder packages
• app registry + feature modules

Common pattern: configuration by import

Sometimes adding support is as simple as adding one import:

import _ "myapp/drivers/mysql"

This works well when the implementation package should stay decoupled from the caller.

Guarding startup failures

Developers often verify early that registration happened correctly:

db, err := sql.Open("sqlite3", dsn)
if err != nil {
    return err
}

This is a form of early validation.

Keeping imports intentional

Because blank imports are unusual, teams often:

• place comments near them
• group them clearly
• use them only when side effects are required

Example:

1. Thinking _ means "ignore this package completely"

It does not ignore the package. The package is still imported and initialized.

2. Expecting to call package functions after a blank import

Broken example:

package main

import _ "fmt"

func main() {
    fmt.Println("hello")
}

Why it fails:

• _ does not create the name fmt
• the package has no usable identifier in this file

Correct version:

package main

import "fmt"

func main() {
    fmt.Println("hello")
}

3. Removing a blank import because it looks unused

Beginners often delete it during cleanup and then get runtime errors.

For example, removing this:

_ "github.com/mattn/go-sqlite3"

Quick reference

Blank import syntax

import _ "package/path"

Meaning

• imports the package
• runs init() functions
• does not create a package name in the file

Use it when

• a package registers itself automatically
• you need side effects only
• you are using registry-based APIs like database/sql or image

Common examples

import _ "github.com/mattn/go-sqlite3"
import _ "image/jpeg"
import _ "image/png"

Typical result

• database driver becomes available
• file decoder becomes available
• plugin registers itself

Important limitation

This is invalid:

import _ "fmt"

func main {
    fmt.Println()
}

Why does Go allow _ in an import?

It allows packages to be loaded for their initialization side effects, usually through init() functions.

Does a blank import execute the package code?

It executes the package initialization code, including variable initialization and init() functions. It does not mean every function runs automatically.

Why is _ "github.com/mattn/go-sqlite3" needed with database/sql?

Because the SQLite driver registers itself with database/sql during initialization. Without that import, sql.Open("sqlite3", ...) would not know about the driver.

Can I use package functions after importing with _?

No. A blank import does not create a package name you can reference in the file.

Is a blank import the same as ignoring an unused import?

No. It is an intentional import for side effects, not a way to silence warnings carelessly.

What is the difference between _ and . in Go imports?

_ imports for side effects only. . imports exported names directly into the current file, which lets you use them without a package prefix.

• Go imports — Basic import syntax helps you understand normal, aliased, dot, and blank imports.
• Blank identifier in Go — The underscore is used in imports, assignments, and loops to intentionally ignore names.
• init() function in Go — Blank imports rely on package initialization behavior.
• database/sql in Go — This package commonly works with side-effect driver registration.
• Go package initialization order — Useful for understanding when imported packages run setup code.
• Go compiler unused import errors — Explains why normal imports must be referenced unless imported as _.
• Plugin and registry patterns — Blank imports are often part of registration-based design.
• Image decoding in Go — A common standard-library example of blank imports in practice.