How do I get SSMS to use the relative path of the current script with :r in sqlcmd mode like SSDT does?
Getting a relative path in SSMS is not that straight-forward since you are not executing the script; SSMS has loaded the script into memory and is executing its text. So the current directory/folder is the default process starting folder. You can see this by running the following in SQLCMD mode in SSMS:

!! PWD


However, I did find a kinda-sorta way to do this. I admit that this is not the super-most ideal way to do this, however, it currently seems to be the only way to get a true relative path (given that setting the path in a variable isn't really "relative" per se).

So what you can do is:


Execute a DOS command to find foo.sql and store the path to that file in a text file in a folder that you can get from SSMS, either because it is a hard-coded path or because it uses an environment variable that is available to both the DOS command and to SQLCMD mode in SSMS
When storing the path in that file, store it as a SQLCMD mode command that sets a variable to that path
Import that text file into SSMS using :r and it will set that variable to the desired path


!! CD C:\ &amp; FOR /F %B IN ('DIR /B /A -HS /S foo.sql') DO ECHO :setvar mypath "%~dpB" &gt; %TEMP%\relative_path.txt

:r $(TEMP)\relative_path.txt

:r $(mypath)\bar.sql


Notes:


The above method assumes only 1 file on the system is named foo.sql. If more than one file has that name, the last one found will be the path set in the relative_path.txt file
Doing the CD C:\ will start at the root of the C: drive. This is probably not the most efficient place to start. If you generally have your SQL files in an area such as C:\Users{YourLogin}\Documents\Visual Studio 2013\Projects, then just change the CD command to get closer to the destination, such as:

!! CD C:\Users\{YourLogin}\Documents\Visual Studio 2013 &amp; FOR ...