I'm having the same issue using JRuby 1.7.10 when trying to invoke rake tasks from a Rails project.
With using JRuby 1.5.6 it complains about the ruby version (1.8.7), but that's only because it's a Rails 4 app and it requires a version >= 1.9.3 (expected)

I'm having the same issue.

When I run fpm in jruby 1.7.18, I get the error shown below. I do not get the same error when running fpm on normal ruby 1.9 .

$ /tmp/jruby/jruby-1.7.18/bin/fpm -s gem -t deb fpm
NoMethodError: undefined method `split' for nil:NilClass
  install_to_staging at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/fpm-1.3.3/lib/fpm/package/gem.rb:190
               input at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/fpm-1.3.3/lib/fpm/package/gem.rb:56
             execute at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/fpm-1.3.3/lib/fpm/command.rb:332
                each at org/jruby/RubyArray.java:1613
             execute at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/fpm-1.3.3/lib/fpm/command.rb:331
                 run at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/clamp-0.6.3/lib/clamp/command.rb:67
                 run at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/fpm-1.3.3/lib/fpm/command.rb:510
                 run at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/clamp-0.6.3/lib/clamp/command.rb:125
              (root) at /tmp/jruby/jruby-1.7.18/lib/ruby/gems/shared/gems/fpm-1.3.3/bin/fpm:8
                load at org/jruby/RubyKernel.java:1087
              (root) at /tmp/jruby/jruby-1.7.18/bin/fpm:23

The offending line:

      gem_bin  = gem_env.select{ |line| line =~ /EXECUTABLE DIRECTORY/ }.first.split(': ').last

I think we have a few issues running together here.

The original report (by @inger) was against 1.6.8, and eventually falls into ant/ant.rb where it tries this:

file, line = caller.detect{|el| el !~ /^#{File.dirname(__FILE__)}/ && el !~ /\.java:/}.split(/:(\d+):?/)

FILE when running from a complete JRuby jar would be something like jar:file:blah.jar!/ant/ant.rb or classpath:ant/ant.rb. If dirname works, it would remove everything after the last /. Then it would compare with caller entries to find the first one that matches.

This is likely a old bug in File.dirname's handling of URLs...that is fixed on current JRuby 1.7.

The second report in here (by @imella) is about being unable to run rake tasks from a Rails project. Unless it's very unusual, that case would usually not be running from the complete jar, and so it is likely a different-but-similar issue. Even if it is the same issue, the File.dirname fixes I mentioned came after 1.7.10, so it needs a re-test.

The third report (by @djhaskin987) is again similar, but does not appear to involve dirname or a complete JRuby jar. This is likely another different-but-similar issue.

I'm going to close this, because I believe the original issue should be fixed.

@inger: Please retest with JRuby 1.7.18 and reopen if it still exhibits the problem.

@imella: Please retest with JRuby 1.7.18 and open a new bug if it still exhibits the problem.

@djhaskin987: Please open a new bug. You're the lucky one that has a current reproduction :-)