-s magic not appearing to work

[Dr Nic]

In the tasty snippet below, the lines + rails_env variables are
passable via "-s lines=10", but they aren't picked up. The commented
out lines were my hack to get the values whilst the magic -s seemed to
elude me.

Am I using -s + local variables incorrectly here?

task :log do
lines ||= 100
rails_env ||= 'production'
# lines = configuration.variables[:lines] || 100
# rails_env = configuration.variables[:rails_env] || 'production'
env = ENV['RAILS_ENV'] || 'production'
run "tail -n #{lines} #{deploy_to}/#{shared_dir}/log/
#{rails_env}.log" do |ch, stream, out|
puts out
end
end

Cheers
Nic

[Jamis Buck]

The problem is two-fold:

1. Capistrano variables are not local variables, but are actually
messages rerouted via method_missing.

2. Ruby auto-vivifies local variables, which can interfere
method_missing calls.

If in Ruby you do:

x = x || 5

The interpreter will see, before executing the line, that it sets a
local variable. Thus, it will first create that variable with a value
of nil.

In your task, then:

lines ||= 100

Ruby cannot know that method_missing will handle that 'lines'
message, so it assumes it is a local variable and dutifully creates a
new local variable with a value of nil, instead of calling
method_missing and getting the value you expect.

I hope that makes sense. Your solution accessing the variables hash
directly is what I'd recommend.

- Jamis

[Nic Williams]

That's the odd part, the lines = lines || 100 doesn't seem to work either.

task :log do
  lines = lines || 100
  rails_env = rails_env || 'production'

  # lines     = configuration.variables [:lines] || 100
  # rails_env = configuration.variables[:rails_env] || 'production'
  env   = ENV['RAILS_ENV'] || 'production'

  run "tail -n #{lines} #{deploy_to}/#{shared_dir}/log/#{rails_env}.log" do |ch, stream, out|
    puts out
  end
end

Still uses 100.

BUT,

  lines = lines || foobar || 100

works if I pass -s foobar=10, so lines might be a variable defined elsewhere perhaps.

At least I now know how it works, so I'll just keep trying variable names til it works in future :)

Cheers
Nic

- Ruby/Rails/Javascript/Web2.0
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[Jamis Buck]

On Apr 11, 2007, at 5:06 AM, Nic Williams wrote:

> That's the odd part, the lines = lines || 100 doesn't seem to work
> either.

Right, it won't, because it is semantically identical to "lines ||=
100".

> BUT,
>
> lines = lines || foobar || 100
>
> works if I pass -s foobar=10, so lines might be a variable defined
> elsewhere perhaps.

Right, because foobar isn't being assigned to, Ruby won't autovivify
a local variable by that name, so when it comes time to evaluate
'foobar', the method_missing hook gets called for it.

> At least I now know how it works, so I'll just keep trying variable
> names til it works in future :)

Yeah, this is a nasty gotcha, unfortunately. :( It would be fixed if
I actually defined a method for every time a variable is
created...but I'm not sure that I like that.

- Jamis

[Wayne E. Seguin]

Nic,

What I do is something like this:

task :log do
run "tail -n #{lines || 100} #{deploy_to}/#{shared_dir}/log/
#{rails_env || ENV["RAILS_ENV"] || "production"}.log" do

|ch, stream, out|
puts out
end
end

Not only does it work great with the -s option, it has the benefit of
being much shorter codewise.

[Wayne E. Seguin]

Oh and you can also shorten the code more using 'shared_path':

run "tail -n #{lines || 100} #{shared_path}/log/...

~Wayne