Reference file in Ruby subshell in Rails app

Question

I am having trouble referencing a file in another directory in my rails app. I have a controller located in my_app/app/controllers/concerns/my_controller with the following line of code:

@value = %x(python ../../lib/assets/python/test.py #{Shellwords.escape(params[:first_name])} 2>&1)

That is running test.py located in my_app/lib/assets/python/test.py with the %x() subshell.

When I reference the file from my desktop, it runs the test.py code correctly. But when I place the script in my lib/assets/python folder I get a cannot find file or directory error.

How should I correctly reference my test.py file so that the %x() command can find it?

What is the environment of the user running the %x(...)?

the Tin Man
– the Tin Man

2015-05-05 00:32:38 +00:00
Commented May 5, 2015 at 0:32 — the Tin Man
– the Tin Man, Commented May 5, 2015 at 0:32

the Tin Man · Accepted Answer · 2015-05-05 00:57:42Z

1

If the PATH isn't set so the user running your code is able to find python then you'll get that error.

Instead of referencing it as python which forces the system to try to locate Python by walking the PATH, use the full path to the interpreter. You can usually find that by typing

which python

at the command prompt, and then putting that into the code replacing the single word python.

Ruby's File class has several very useful methods for finding the path from a directory to another, or to a specific file. Look at:

I generally use realpath since it checks to see that the target actually exists before returning a path to it.

You could use it something like:

File.realpath('../../path/to/file', File.dirname(__FILE__))

which should return a path relative to the script that is currently being executed.

You can reference from the running script using:

File.realpath('../../path/to/file', File.dirname($0))

You'll need to figure out whether you want to base your path from __FILE__ or $0 and what the differences are.

edited May 5, 2015 at 0:57

answered May 5, 2015 at 0:33

the Tin Man

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3 Comments

jdesilvio Over a year ago

that works when I use the full file path to the test.py file, but how can I reference the file from within the app. /Users/me/anaconda/bin/python /Users/me/workspace/my_app/lib/assets/python/test.py works but, when I reference the file from within the app I get /Users/me/anaconda/bin/python: can't open file '../../lib/assets/python/test.py': [Errno 2] No such file or directory

the Tin Man Over a year ago

See the updated information about using File's methods.

jdesilvio Over a year ago

I tried pretty much every combo I could think of and finally realized why it wasn't working, I needed to escape the File.realpath command. @value = %x(/Users/me/anaconda/bin/python #{Shellwords.escape(File.absolute_path('lib/assets/python/test.py'))})

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