Loosely related software tips

Ant's sshexec task calling Ant targets on server

I had Ant running OK on a Linux server. By this I mean that when I ssh'd to the server I could type 'ant' and it would run the default target in build.xml (saved in my user home directory).

I wanted a way to be able to securely call server-side Ant targets from Ant running on my client computer. The solution to this would seem to be the sshexec ant task (one of the optional tasks introduced in Ant 1.6).

I had a spot of trouble getting it working, for reasons I couldn't fathom. It would work with simple Unix commands like 'ls', but a simple attempt to use sshexec to execute the command 'ant' on the server should have resulted in the default target being run, but it didn't. It did, however, work when I used Putty to ssh to the server.

I eventually discovered that, for some reason, when sshexec connected to the server, it had a load of environment variables missing that were there when Putty connected to the server. The following ant task showed this:

<sshexec host="${server.host}" 
    username="${server.username}"
    password="${server.password}"
    command="bash -c set"/>

This returned a list of the environment variables that were set on the server when sshexec connected. Doing 'bash -c set' through Putty showed a much improved list that had JAVA_HOME, ANT_HOME, and the path to ant.sh in the path.

I never did figure out why this was happening - I don't know much at all about Unix. I did find a couple of unanswered forum posts indicating that others had the same problem. I messed about for a while, and figured it might be something to do with sshexec creating a 'dumb' terminal (whatever that may be...), but that didn't get me anywhere.

I did get it working, however, in a way that would undoubtedly cause anyone knowing Unix to say "well, obviously". The trick was to do several commands in the one line, separating them with ;, setting the necessary environment variables first (with export), and using the full path to ant.

<target name="-runAntOnServer"
    description="Sorts out environment variables
    and so on that are necessary to run ant on 
    the server. The antOptions property can be 
    passed in to specify options to be passed 
    to ant.">
  <sshexec host="${server.host}"
      username="${server.username}"
      password="${server.password}"
      command="export JAVA_HOME=/usr/local/jdk;
      export ANT_HOME=/usr/local/ant;
      /usr/local/ant/bin/ant ${antOptions}"/>
</target>

I'm guessing the directories I set are probably pretty common, but they may well be different on different systems.

To call a specific ant target (e.g. called 'copyFiles') on the server (in build.xml saved in the user home directory) is simple:

<antcall target="-runAntOnServer">
  <param name="antOptions" value="copyFiles"/>
</antcall>

posted by bromley @ Thursday, July 21, 2005 0 comments

Why I've started this blog

I'm a bit of a perfectionist when it comes to making software: I like to be satisfied that I've done things as well as I could. This is not to say that I make perfect software (if only), more that I spend a considerable proportion of my time trying to get things right, as opposed to getting things merely working. I do like to think that my approach pays off in the long run...

When I'm developing software I'm usually in one of two 'modes':

• Work-mode - getting things working, getting things done. All fine until I discover a niggling little issue that either obstructs progress altogether, or just gives me the feeling that something isn't quite right and that there must be a better way. That's when I step into research-mode...
• Research-mode - scouring the web for information relating to my problem. Quite often there isn't much, or what there is is incomplete, offering conflicting information, or too complicated for my head :s

Anyway, at the end of one of my little voyages of research-mode discovery I tend to feel a little guilty for not sharing my findings with the rest of the world. After all, if someone else had posted a clear solution to the problem, I wouldn't have a sore head from 10 hours of reading incoherent and conflicting forum posts.

So this blog is my answer to these feelings of guilt. If I get around to it, I'll post some info from time to time. It'll probably be obvious stuff to most people that stumble across it, but hopefully it'll be useful to someone. If not then at least Google might find it for me when I'm searching for the same problem again in a few months...

posted by bromley @ Thursday, July 21, 2005 0 comments