A conditional ant exec task

I can’t say I’m a fan of the Apache Ant build tool but that’s what our project uses so I’ve been trying to wrap my small brain around it enough to make some small changes to our configurations.

Today I needed to call an exec task in a build.xml file on the condition that the executable is in the user’s $PATH. This is what I came up with. Other suggestions are welcome. In my case I needed to execute svn (because the svn task doesn’t provide an api for the svn info command) but the general conditional will apply to any executable.

<target name="buildInfo" depends="canDoSvn,svnInfo/>

<target name="canDoSvn">
<property environment="env" />
<condition property="can.do.svn">
<and>
<available file="${projectsDir}/${proj}/.svn" type="dir" />
<available file="svn" type="file">
<filepath>
<pathelement path="${env.PATH}"/>
</filepath>
</available>
</and>
</condition>
</target>

<target name="svnInfo" if="can.do.svn">
<exec dir="${projectsDir}"
executable="svn"
outputproperty="svnInfoOut"
failonerror="false"
failifexecutionfails="false">
<arg line="info ${proj}"/>
</exec>
</target>

To kick things off, the buildInfo target is called elsewhere in the build script. This target defines dependancies for two other targets that get called in listed order.

In the canDoSvn target I test if the file svn can be found in the user’s $PATH. To do this I set the property task’s environment attribute to env which gives me a handle on the user’s PATH environment variable: ${env.PATH} . The path attribute of pathelement converts the colon-separated list of env.PATH to a directory search list used by the available task.

I also test if there is an .svn directory available. This is to verify that the project being built is from an svn working directory. Obviously svn info would fail otherwise.

If these two conditions are met, the can.do.svn property is set to true and allows the svnInfo target to run when called as a dependancy of buildInfo. I’m defining canDoSvn as a dependancy rather than calling it directly with antcall because with the latter method the can.do.svn property is not accessible outside the canDoSvn target, so the svnInfo condition is never met.

To be thorough, I still need to add a condition that the svn file is executable. I’m not sure how to do that yet.

In my case, I’m guaranteed the ant build is executing on a Linux system, so I don’t know or have to worry about what will happen if this technique is attempted in MS Windows.

Update: From the documentation, it looks like the svn task does indeed interface the the svn info command, using the status element. Anyhoo, I don’t have the svn task installed on our systems so wrapping the svn command line stands.