How to return a value from a phing target?

Question

I would like to have a foreach task like this, which iterates over all the files/directories in a directory "A" -

<foreach param="dirname" absparam="absname" target="subtask">
  <fileset dir="${dir.destination}/${dir.subdir}/">
    <type type="file" />
    </fileset>
</foreach>

The target "subtask" should check if the counterpart of the file/folder exists in another directory "B" (I am comparing directory A and B basically), and return either of the following if it does not -

• a flag.
• name of the file.

Following is some code for reference -

<target name="subtask">
    <if>
        <filesmatch file1="${file1}" file2="${file2}"/>
        <then>
            Return false. But how?
        </then>
        <else>
            Return true of name of the file. How?
        </else>
    </if>
</target>

Note - It is okay if this can be done without calling a target. I am not sure if the logic can be fit inside the foreachtask itself. Could not find any such thing in the phing documentation.

Basically, I should be having the list of file names which are not present in the directory B, by the end of the loop.

You may also read this question of mine, if you can give some pointers to solve the issue in some other way.

Update

Rephrasing this question, since I feel that the problem description is not clear. The phing documentation says, a target has no return value -

Targets are collections of project components (but not other targets) that are assigned a unique name within their project. A target generally performs a specific task -- or calls other targets that perform specific tasks -- and therefore a target is a bit like a function (but a target has no return value).

I don't understand why is it designed so. With this bounty, I would like to know if there is some workaround for me other than having to define my own custom tasks in PHP, and then set properties -

$this->getProject()->setNewProperty('modifiedElements', implode("\n\n",$modifiedElementsArray));

which can be accessed in the build file

I have a target which checks whether my production code base has any differences from the expected git revision -

<target name="compare_prod_with_expected_revision">
        <input propertyname="box.git_version">
            Enter git version of the production codebase:
        </input>
        <exec command="git reset --hard ${box.git_version}" dir="${dir.scratchpad}" />
        <!-- Scratchpad brought to revision ${box.git_version} -->

        <echo>Verifying whether production is at revision ${box.git_version}..</echo>
        <exec command="diff -arq --exclude='.git' ${dir.scratchpad}/${dir.subdir} ${dir.destination}/${dir.subdir}" outputProperty="diffList"/><!-- #TODO ignore.swp files in this step. Diff says .swp files present in production code. But doing ls -a there does not show the same. -->
        <php function="strlen" returnProperty="productionDeviationFromExpectedBranch"><!-- #TODO - find how to not show this step during build process. Put it in a target and set hidden="true" -->
            <param value="${diffList}"/>
        </php>
        <if>
            <equals arg1="${productionDeviationFromExpectedBranch}" arg2="0" />
            <then>
                <echo>Verified production is at revision ${box.git_version}</echo>
            </then>
            <else>
                <echo>Differences -  </echo>
                <echo>${diffList}</echo>
            </else>
        </if>
    </target>

Now, I want to phingcall this target and would like to access some property set by it.

Answer 1

I think I understood your purposes, and at the same time I feel like you chosen not the optimal tool of doing this.

As you mentioned in your question, official documentation on phing is clear about tasks (targets):

Targets are collections of project components (but not other targets) that are assigned a unique name within their project. A target generally performs a specific task -- or calls other targets that perform specific tasks -- and therefore a target is a bit like a function (but a target has no return value).

Targets should be components of your application, which execute specific task, atomic task. It could be initialization task, configuration fetching, compilation step, assets preparation and dumping, deployment task, clean-up task, etc. There's no "output", returned by target in the standard sense, but the result of target execution is the success of execution itself: success or failure.

One should not try to put way too much of logic into such project targets, as it is not intended to do complicated calculations, do heavy logical decisions, etc. I mean, Phing can do it, such things are possible, but this setup would be bulky, unreadable, and hard to scale/re-factor.

With Phing you can easily define conditional execution and branching of logical flow, you may define the sequence of execution of tasks (dependencies) - this is what makes it laconic and elegant. Keep targets as simple as possible, split the project into small, finished logical tasks.

Based on the projects I've been working with, the biggest targets, probably, were initialization stage and configs fetching. Here's some example, to understand what it might contain, I took it from real project:

<target name="init_configuration">
    <echo msg="Define initial configuration for the deployment..." />
    <if>
        <not>
            <isset property="host" />
        </not>
        <then>
            <property name="host" value="dev" override="true" />
            <echo message="The value of hostname has been set to ${host}" />
        </then>
        <else>
            <echo message="The value of hostname is ${host}" />
        </else>
    </if>
    <if>
        <not>
            <isset property="version" />
        </not>
        <then>
            <property name="version" value="1.0.0" override="true" />
            <echo message="The value of version has been set to ${version}" />
        </then>
        <else>
            <echo message="The value of version is ${version}" />
        </else>
    </if>

    <property name="host_credital_file" value="config/hosts/${host}.properties" />
    <property file="${host_credital_file}" />
    <available file="${host_credital_file}" property="hostfilefound" value="true"/>
    <fail unless="hostfilefound" message="Missing Hostfile configuration file (${host_credital_file})!" />

    <echo msg="Configuration is done" />
</target>

Other targets were extremely simplistic, they are normally – 1-5 lines long, and do only small purpose, small task. This would be, probably, the best recommendation when working with Phing.

---

The logic which you are trying to put on shoulders of Phing is possible, but would be extremely bulky.

Consider the point: how much quicker, easier, and more readable the same thing could be done with simple bash script in your example. Or even to write small CLI utility in PHP, which will do the job elegantly and quick. After that in Phing you'll leave parametric target which will execute this "revision diff script" from CLI.

Phing is a great tool for what it is designed for, but it can't be an optimal choice for every purpose. Just do not put way to much responsibility and logic into it.

As a workaround, for more complicated things it's better to combine Phing with with something specialized: bash scripting, PHP CLI, nodeJS (+ Grunt, Gulp, etc)... and just to add calls of a Phing targets later.

Answer 2

This is the way I managed to have targets which behave like functions:

<target name="-console-cmd-return-property" hidden="true">
    <exec command="${command}" checkreturn="${checkreturn}" logoutput="${logoutput}" outputProperty="${outputProperty}"/>
</target>

It gets invoked like this:

<phingcall target="--console-return-property">
    <property name="command" value="ps auxwww"/>
    <property name="checkreturn" value="true"/>
    <property name="logoutput" value="false"/>
    <property name="outputProperty" value="ps_output"/>
</phingcall>

Of course it works because it relies on existing exec, and it is not generic...