Eval. get the console result into a variable

Ruby
1

I’m creating a web service using Sinatra to run ruby code, so for that
I’m using something like:

begin
eval(code)
rescue Exception => resRun
end

but I need to get access to the result of the code run in the console…
so if code is something like:
puts “example”

I want to get the output “example” in a variable

How is it possible to do it?

2

Hi,

The kernel methods “print”, “puts” etc. actually call $stdout.write and
$stdout.puts. So you could simply create your own object with a write
and puts method and (temporarily) change $stdout to this object:

class OutputCollector

attr_reader :content

def write x
@content += x.to_s
end

def puts x
write x.to_s + “\n”
end

def initialize
@content = ‘’
end

end

this changes $output to an instance of OutputCollector, executes the

block (all output will be written to the OutputCollector), changes

$stdout back to the default value (given by STDOUT) and returns the

collected output

def catch_output
coll = OutputCollector.new
$stdout = coll
yield
$stdout = STDOUT
coll.content
end

caught = catch_output do
print ‘abc’
print 123
end

show collected output

p caught

Of course, you should be careful when evaluating user code. I would at
least create a new Thread with an appropriate value of $SAFE.

3

Not working in my case since what we have inside is an eval with a
testcase inside

Jan E. wrote in post #1051635:

Hi,

The kernel methods “print”, “puts” etc. actually call $stdout.write and
$stdout.puts. So you could simply create your own object with a write
and puts method and (temporarily) change $stdout to this object:

4

What do you mean? What isn’t working?

5

Did you try something simple like

caught = catch_output do
eval ‘print 1’
end
p caught

If this works (it should), then there’s probably something wrong with
the string you evaluate. Does it even have output?

6

Jan E. wrote in post #1051815:
I didn’t get anything

What do you mean? What isn’t working?

7

Thanks for the help… but it is more difficult like it looks like
so i’m gonna do it other way… putting the code in a file and then
calling resRun= ruby #{fileNameRuby}

and in case resRun is empty means that there was an error in the code so
i have to do it like resRun=eval(code)

Thanks for your help :slight_smile:

Jan E. wrote in post #1051820:

Did you try something simple like

caught = catch_output do
eval ‘print 1’
end
p caught

If this works (it should), then there’s probably something wrong with
the string you evaluate. Does it even have output?