Programatically associate file extensions with application on Windows

Use Ftype & Assoc to fix this (and it is scriptable).

Use Assoc to get the filetype

>Assoc .txt

gives you:

.txt = txtfile

Then

>Ftype txtfile=C:\Program Files (x86)\Notepad++\notepad++.exe %1

Once you know the file type you can use Ftype to associate it with an action.

This would work for .php files (just plop them in a batch file)

Assoc .php=phpfile
Ftype phpfile="C:\Program Files (x86)\Notepad++\notepad++.exe" %1

And you can copy these lines to add other text-based files as you would like.

Here's a script that worked for me on Windows 10

$exts=@("txt","log","csproj","sql","xml","flobble")
echo "## setting up file associations"
foreach ($ext in $exts){
    $extfile=$ext+"file"
    $dotext="." + $ext
    cmd /c assoc $dotext=$extfile
    cmd /c "ftype $extfile=""C:\Program Files (x86)\Notepad++\notepad++.exe"" ""%1"""
    echo ""
}

• Needs to be run in an administrator (elevated) PowerShell window.
• Explorer immediately refreshed and showed new file icons.

https://gist.github.com/timabell/bc90e0808ec1cda173ca09225a16e194

Thanks to the other answers for the information I needed to make this work.

At the minimum, you need to create one registry key which gives notepad++ an ID and path and then one for each extension you wish to register to use it.

To create the ID and path (check the path points to the correct location):

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\notepad_pp]
@=""

[HKEY_CLASSES_ROOT\notepad_pp\shell]

[HKEY_CLASSES_ROOT\notepad_pp\shell\open]

[HKEY_CLASSES_ROOT\notepad_pp\shell\open\command]
@="\"C:\\Program Files (x86)\\Notepad++\\notepad++.exe\" \"%1\""

and then keep repeating the next bit, one for each extension (in this example, .pl is for Perl):

[HKEY_CLASSES_ROOT\.pl]
@="notepad_pp"

Save this file with the extension .reg and you should now be able to re-associate all the extensions just by double-clicking on this file and confirming you want to import the entries into the registry.