I have a controller method written along these lines:
begin
system("/script/that/generates/output > text_file")
var += IO.readlines(“text_file”)
send_data var, :filename => “attachment.txt”, :disposition =>
‘attachment’, :type => ‘text/plain’
rescue
flash[:error] = “Error message here”
redirect_to :action => ‘error_page’
end
What this is supposed to do is send the contents of the text file plus
some other data directly to the user. The problem is, of course, that
the system call will not run from a Rails controller as this is
apparently considered very naughty. I could instead use backgroundrb to
generate the file (the same system call is fine as part of a
backgroundrb job) and then e-mail it to users but I would rather send it
immediately as the attachment is virtually instantaneous. Is
backgroundrb really the only way to do that? It seems a bit much for
such a small task.
I’m not sure what you’re talking about. You can make system calls.
I did a search of this group and found advice against system calls.
You might want to check your log files to see what they tell you about
your
current situation.
They tell me absolutely nothing, unfortunately. The system call fails
with no message in the logs, and yet I can run the same system call
successfully on the command line as the same user. My assumption was
that system calls were not allowed but perhaps I was mistaken and there
is something else very strange going on.
When you say ‘fails’ I assume you mean you just can’t find the file you
expect to be created anywhere on your system.
That’s part of it. I tried setting things up as in this pseudocode:
begin
logger.info(“ONE”)
first system call
logger.info(“TWO”)
second system call
logger.info(“THREE”)
rescue
redirect to the error page
end
In this case the expected file does not appear, “ONE” is found in the
log but not “TWO” or “THREE”, and the app. redirects to the error page.
It seems that the system call is a complete failure with no explanation.
When you say ‘on the command line’, do you mean from irb or
script\console ?
Or do you mean ‘from the OS command line’? If the latter, it’s
potentially
a permissions issue.
I tried it on the OS command line. I thought that it might be
permissions, but I’d run script/server as a user that has write
permission to the relevant directory. I’d also expect some sort of
permissions error in the logs from the system call but none were to be
found. I hadn’t tried it with irb or script/console but I just did and
it worked as expected. Very odd…
Thanks for taking the time to make some suggestions!
The system call fails with no message in the logs,
and yet I can run the same system call successfully
on the command line as the same user.
When you say ‘fails’ I assume you mean you just can’t find the file you
expect to be created anywhere on your system. If there’s something
visible
happening that you can report, it would help.
When you say ‘on the command line’, do you mean from irb or
script\console ?
Or do you mean ‘from the OS command line’? If the latter, it’s
potentially
a permissions issue. Note that your rails app runs as a different user
than
you. Try to run it as that user and see what happens.
Also, in rails system() or backticks are only not advised, when they end up blocking the master mongrel process for a real long time, otherwise you can happily use system() or within your programs
without problems.
Thanks - evidently I had jumped to the wrong conclusion.
It looks like one of the object methods included in #{} within the
system call is failing; it’s strange that there’s no error message but
that must be the cause.
Thanks - evidently I had jumped to the wrong conclusion.
It looks like one of the object methods included in #{} within the
system call is failing; it’s strange that there’s no error message but
that must be the cause.
Sometimes exception handling code can eat useful error messages,
especially if you don’t capture and display the exception object, you
may miss useful info. When diagnosing things, I occasionally find it
is useful to comment out the rescue clause and let the error bubble to
the surface. Alternatively, capture it (e.g. rescue Exception => e)
and display in your rescue clause with a logger or similar output.
When you say ‘on the command line’, do you mean from irb or
it worked as expected. Very odd…
Thanks for taking the time to make some suggestions!
Rather than using system() you can use backticks echo "hello" to
capture output of a command, which will tell you more about, what
happened to the call.
Also, in rails system() or backticks are only not advised, when they end up blocking the master mongrel process for a real long time, otherwise you can happily use system() or within your programs
without problems.
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