How to set a VSPROPS variable only if it does not already exist?

问题

Say I've got a .vsprops file that is used in a solution. In that file, various variables are defined such as int_dir for intermediate build results and log_dir for the log results.

Usually, these variables get set to default values (relative to the solution).

For me, I'd like to set these two variables to my ramdisk (R:), i.e. no longer

$(SolutionDir)\intermediate

but

R:\myproject\intermediate

If I change the .vsprops file directly, the source control (Git) will mark it as modified.

Is there a way in VSPROPS so that I could check maybe an environment variable and if this variable is not set, the default is used?

If this is not possible, I'd also be interested in a solution for Git to overcome this (but not --assume-unchanged and not .gitignore because maybe other changes in that file could be relevant).

回答1:

A pure Git solution could use a gitattribute filter driver:

It would involve a smudge script, executed on git checkout, which would:

• detect if you want to change $(SolutionDir) (for instance, test for an environment variable with the updated path in it)
• detect the right file (xxx.vsprops.tpl) content (the script doesn't know the file names or path it operates on)
• generate the actual .vsprops from a .vsprops.tpl (template file) which is the one being versioned (the .vsprops is no longer versioned)

You can add a clean script which would preserve (on git commit) all the modification done in the .vsprops file back to the .vsprops.tpl, except for the $(SolutionDir) line.

来源：https://stackoverflow.com/questions/12968865/how-to-set-a-vsprops-variable-only-if-it-does-not-already-exist