windows - Resolve absolute path from relative path and/or file name

Question

Is there a way in a Windows batch script to return an absolute path from a value containing a filename and/or relative path?

Given:

".."
"..somefile.txt"

I need the absolute path relative to the batch file.

Example:

• "somefile.txt" is located in "C:Foo"
• "test.bat" is located in "C:FooBar".
• User opens a command window in "C:Foo" and calls Barest.bat ..somefile.txt
• In the batch file "C:Foosomefile.txt" would be derived from %1

Answer 1

In batch files, as in standard C programs, argument 0 contains the path to the currently executing script. You can use %~dp0 to get only the path portion of the 0th argument (which is the current script) - this path is always a fully qualified path.

You can also get the fully qualified path of your first argument by using %~f1, but this gives a path according to the current working directory, which is obviously not what you want.

Personally, I often use the %~dp0%~1 idiom in my batch file, which interpret the first argument relative to the path of the executing batch. It does have a shortcoming though: it miserably fails if the first argument is fully-qualified.

If you need to support both relative and absolute paths, you can make use of Frédéric Ménez's solution: temporarily change the current working directory.

Here's an example that'll demonstrate each of these techniques:

@echo off
echo %%~dp0 is "%~dp0"
echo %%0 is "%0"
echo %%~dpnx0 is "%~dpnx0"
echo %%~f1 is "%~f1"
echo %%~dp0%%~1 is "%~dp0%~1"

rem Temporarily change the current working directory, to retrieve a full path 
rem   to the first parameter
pushd .
cd %~dp0
echo batch-relative %%~f1 is "%~f1"
popd

If you save this as c:empexample.bat and the run it from c:UsersPublic as

c:UsersPublic>empexample.bat ..windows

...you'll observe the following output:

%~dp0 is "C:emp"
%0 is "empexample.bat"
%~dpnx0 is "C:empexample.bat"
%~f1 is "C:Userswindows"
%~dp0%~1 is "C:emp..windows"
batch-relative %~f1 is "C:Windows"

the documentation for the set of modifiers allowed on a batch argument can be found here: https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/call