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How to Get the File Extension from a Full Path in Batch Script

When you are processing files in a batch script, you rarely work with the entire path. A more common task is to deconstruct the path to get its individual components: the parent folder, the filename, or, most frequently, the file extension. Knowing a file's extension allows you to perform actions based on its type. For example, moving all .jpg files to one folder and all .txt files to another.

This guide will teach you the simple and powerful built-in methods for extracting a file's extension using parameter expansions. You will learn how to apply this technique to both variables and script arguments, making it a fundamental skill for any file management script.

The Core Method: FOR Loop Parameter Expansions​

The most versatile method for getting a file extension from a path stored in a variable is to use a FOR loop. Even when processing a single path, the FOR command gives you access to special "tilde modifiers" that can break a path into its constituent parts.

The key modifier for this task is ~x.

  • FOR %%I IN ("path") DO ...: This sets up a loop that will run once, with %%I holding the full path.
  • %%~xI: Inside the loop, this syntax expands %%I to its extension only. The extension includes the dot (.).

Alternative Method: For Script Arguments (%~x1)​

If the file path is being passed to your script as a command-line argument (e.g., %1, %2), you don't need a FOR loop. You can apply the tilde modifier directly to the argument variable.

The syntax is: %~x1

  • %1: The first command-line argument.
  • ~x: The modifier to extract the extension.

This is the simplest and most direct method for handling paths that are passed into your script.

Basic Example: Getting an Extension from a Path​

Let's extract the extension from a full file path using the FOR loop method.

@ECHO OFF
SET "FullFilePath=C:\Users\Admin\Documents\Annual Report Q4.docx"

ECHO The full path is: "%FullFilePath%"

FOR %%F IN ("%FullFilePath%") DO (
    ECHO The extension is: %%~xF
)

As you can see in the output, the %%~xF modifier correctly isolates the extension, including the dot.

The full path is: "C:\Users\Admin\Documents\Annual Report Q4.docx"
The extension is: .docx

Storing the Extension in a Variable​

To use the extension in your script's logic, you need to capture it in a variable.

@ECHO OFF
SET "FullFilePath=C:\Downloads\installer.msi"
SET "FileExtension="

FOR %%F IN ("%FullFilePath%") DO (
    SET "FileExtension=%%~xF"
)

ECHO The file has a%FileExtension% extension.
IF /I "%FileExtension%"==".msi" (
    ECHO This is a Windows Installer package.
)

Output:

The file has a.msi extension.
This is a Windows Installer package.

Common Pitfalls and How to Solve Them​

Problem: The File Has No Extension​

If you run this logic on a file that does not have an extension (e.g., a file named LICENSE), the ~x modifier will return an empty string.

@ECHO OFF
SET "FilePath=C:\Project\LICENSE"
SET "FileExtension="

FOR %%F IN ("%FilePath%") DO SET "FileExtension=%%~xF"

IF DEFINED FileExtension (
    ECHO The extension is: %FileExtension%
) ELSE (
    ECHO The file has no extension.
)

Output:

The file has no extension.
note

This behavior is predictable and can be easily checked with an IF DEFINED statement.

Problem: The Path is a Directory​

Similarly, if you provide a path to a directory, the ~x modifier will return an empty string because directories do not have extensions. This is another case where checking if the resulting variable is defined is a useful validation step.

Practical Example: Sorting Files into Folders by Extension​

This is a classic and highly useful script. It iterates through all files in the current directory, gets the extension of each file, creates a folder named after that extension (if one doesn't already exist), and then moves the file into it.

@ECHO OFF
SETLOCAL ENABLEDELAYEDEXPANSION

ECHO --- File Sorter ---
ECHO Sorting all files in the current directory into subfolders by extension...
ECHO.

FOR %%F IN (*.*) DO (
    REM Get the file extension.
    SET "ext=%%~xF"
    
    REM We need to handle the case where the file has no extension.
    IF "!ext!"=="" (
        SET "ext=NoExtension"
    ) ELSE (
        REM Remove the dot from the extension for the folder name.
        SET "ext=!ext:~1!"
    )
    
    REM Create the destination folder if it doesn't exist.
    IF NOT EXIST "!ext!\" MKDIR "!ext!"
    
    REM Move the file into the appropriate folder.
    MOVE "%%F" "!ext!\"
)

ECHO.
ECHO --- Sorting complete ---
ENDLOCAL

Conclusion​

Extracting a file's extension is a simple but powerful capability in Windows Batch, made possible by the tilde (~) modifiers.

  • To get the extension from a path stored in a variable, use a FOR loop and the %%~xF syntax.
  • To get the extension from a command-line argument, use the direct %~x1 syntax.

This is a fundamental technique for writing any script that needs to perform actions based on file type, allowing for powerful and flexible file management automation.

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