Temporarily establish file associations

Question

I have a portable development tool that I want to use on other PCs. I would like to establish a file association so that clicking on a file opens the tool. Then, when I finish, I want to cancel or reset the file association on this PC.

Is there any way to do this? Perhaps from a batch file?

Answer 1

Well, you can use the commands ftypeand assocto create or delete a file type association:

ASSOC .foo=FooFile
FTYPE FooFile=X:\Foo\foo.exe %1 %*

You can delete them later with

FTYPE FooFile=
ASSOC .foo=

: -, . Subversion. : set.cmd reset.cmd; , . set.cmd , , .

, .

@echo off
setlocal enableextensions enabledelayedexpansion
rem Debug flag. Generates a little more output; un-set if undesired
set DEBUG=1

rem Parse arguments and help
if [%1]==[] goto Usage
if [%2]==[] goto Usage

rem Find out whether the association is taken
for /f "usebackq tokens=2* delims==" %%x in (`assoc .%1 2^>nul`) do set assoc_old=%%x
if defined DEBUG (
    if defined assoc_old (echo Association already defined: [%assoc_old%]) else (echo Association not yet taken)
)

rem Find a new, unused association
rem Note that we assume that we find one, eventually. This isn't guaranteed, but we'll ignore that for the moment
rem Otherwise this loop might run forever
:loop
    set assoc_new=My.%1.%RANDOM%
    if defined DEBUG echo Trying new association (%assoc_new%)
    assoc .%1 >nul 2>nul
    if errorlevel 1 (
        set assoc_new=
        if defined DEBUG echo Didn't work out
    ) else (
        if defined DEBUG echo Found one! \o/
    )
if not defined assoc_new goto loop

if defined DEBUG echo Writing reset batch file
echo @echo off>reset.cmd
echo assoc .%1=%assoc_old%>>reset.cmd
echo ftype %assoc_new%=>>reset.cmd

if defined DEBUG echo Writing setting batch file
echo @echo off>set.cmd
echo assoc .%1=%assoc_new%>>set.cmd
echo ftype %assoc_new%=%2 %%1>>set.cmd

goto :eof

:Usage
echo.Usage
echo.  %~nx0 type command
echo.
echo.  type      is the file type to override, such as docx or txt.
echo.            No dot before it is necessary.
echo.  command   is the command to perform on that file.
echo.            %%1 is automatically appended at the end.
echo.            If the command includes spaces, surround it with quotes.
echo.
echo.Example
echo.  %~nx0 txt notepad

exit /b 1