'make -n' equivalent for ant - ant

Question

According to the man page of make, -n option does the following job:
Print the commands that would be executed, but do not execute them.
I am looking for an option which acts the same in Apache Ant.

Answer 1

Horrific, but here it is. We can hack the targets at runtime using some code inside a <script> tag*. The code in do-dry-run below sets an unless attribute on each of your targets, and then sets that property so that none of them executes. Ant still prints out the names of targets that are not executed because of an unless attribute.
*(JavaScript script tags seem to be supported in Ant 1.8+ using the Oracle, OpenJDK and IBM versions of Java.)
<?xml version="1.0" encoding="UTF-8"?>
<project default="build">
<target name="targetA"/>
<target name="targetB" depends="targetA">
<echo message="DON'T RUN ME"/>
</target>
<target name="targetC" depends="targetB"/>
<target name="build" depends="targetB"/>
<target name="dry-run">
<do-dry-run target="build"/>
</target>
<macrodef name="do-dry-run">
<attribute name="target"/>
<sequential>
<script language="javascript"><![CDATA[
var targs = project.getTargets().elements();
while( targs.hasMoreElements() ) {
var targ = targs.nextElement();
targ.setUnless( "DRY.RUN" );
}
project.setProperty( "DRY.RUN", "1" );
project.executeTarget( "#{target}" );
]]></script>
</sequential>
</macrodef>
</project>
When I run this normally, the echo happens:
$ ant
Buildfile: build.xml
targetA:
targetB:
[echo] DON'T RUN ME
build:
BUILD SUCCESSFUL
Total time: 0 seconds
But when I run dry-run, it doesn't:
$ ant dry-run
Buildfile: build.xml
dry-run:
targetA:
targetB:
build:
BUILD SUCCESSFUL
Total time: 0 seconds

Answer 2

Ant has no dry-run option as make or maven have. But you could run the ant file step by step it in debugging mode under eclipse.

Answer 3

No I belive. There is no such way by default in Ant. And many unstisfying attempts you would find on google. But I have searched once and was unsuccessful.

Answer 4

It would be a useful feature, but not easily implemented.
Make and ANT are architecturally quite different. ANT doesn't run external OS commands, instead, most ANT "tasks" execute within the same Java thread.
It would be possible to emulate a "dry run" as follows:
<project name="Dry run" default="step3">
<target name="step1" unless="dry.run">
<echo>1) hello world</echo>
</target>
<target name="step2" depends="step1" unless="dry.run">
<echo>2) hello world</echo>
</target>
<target name="step3" depends="step2" unless="dry.run">
<echo>3) hello world</echo>
</target>
</project>
Running ANT as follows will print the target name but won't execute the enclosed tasks:
$ ant -Ddry.run=1
Buildfile: build.xml
step1:
step2:
step3:
BUILD SUCCESSFUL
Total time: 0 seconds

Answer 5

Create a special target in your buildscript that does some echoing only i.e. to check whether properties, path .. are resolved correctly.
see https://stackoverflow.com/a/6724412/130683 for a similar question answered.
For checking the details of your ant installation use ant -diagnostics