Eclipse: how to introduce variables in .target and .launch files

Right now we have .target and .launch files in eclipse that point to specific hard-coded locations. How do I introduce new variables and assign them in eclipse, variables that are local to each developer.

Here is an example. I want to set up a projectlocation variable, but don't know where to set it:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?pde version="3.6"?>

<target name="OSGI-installed"&g开发者_StackOverflowt;
<locations>
<location path="${projectlocation}\trunk\CACHE\junit4.TransformedRepo" type="Directory"/>
<location path="${projectlocation}\trunk\CACHE\mokito.repo" type="Directory"/>
<location path="${projectlocation}\trunk\CACHE\p2EDARepo" type="Directory"/>
<location path="${projectlocation}\trunk\CACHE\p2BundlesRepo" type="Directory"/>
</target>

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Go to this setting: windows/preferences/Run/Debug/String Substitutions and add in your variables such as ${variableName}