Ant conditions - which comes first 'if' or 'unless'

问题

Question

If an ant target uses both if and unless, which is evaluated first?

Example

What comes first, the chicken or the egg? . . .

<target name="prepare" if="chicken" unless="egg" >
    <echo>Dinner time. Chicken is served!</echo>
</target>

Would ant evaluate the chicken property first? Or the egg property?

回答1:

It isn't really a question of evaluation, since the properties either are or are not set before the target gets called.

EDIT: I looked at the 1.8.1 source and the logic is as follows:

if (!testIfAllows()) {
    project.log(this, "Skipped because property '" + project.replaceProperties(ifCondition)
            + "' not set.", Project.MSG_VERBOSE);
    return;
}
if (!testUnlessAllows()) {
    project.log(this, "Skipped because property '"
            + project.replaceProperties(unlessCondition) + "' set.", Project.MSG_VERBOSE);
    return;
}

So the unless won't matter unless the if passes. But keep in mind, these don't have anything to do with evaluating properties. It just looks them up to see if they are set.

来源：https://stackoverflow.com/questions/4084014/ant-conditions-which-comes-first-if-or-unless