Ruby/Rails: pass arguments to command line application from rake task

Question

How do you pass arguments from within a rake task and execute a command-line application from Ruby/Rails?

Specifically I'm trying to use pdftk (I can't find a comparable gem) to split some PDFs into individual pages. Args I'd like to pass are within < > below:

$ pdftk <filename.pdf> burst output <filename_%04d.pdf>

Answer 1

In the ruby code for your rake task:

`pdftk #{input_filename} burst output #{output_filename}`

You could also do:

system("pdftk #{input_filename} burst output #{output_filename}")

system() just returns true or false. backticks or %x() returns whatever output the system call generates. Usually backticks are preferred, but if you don't care, then you could use system(). I always use backticks because it's more concise.

More info here: http://rubyquicktips.com/post/5862861056/execute-shell-commands

Answer 2

e.g. as:

filename = 'filename.pdf'
filename_out = 'filename_%04d.pdf'

`pdftk #{filename} burst output #{filename_out}`

or

system("pdftk #{filename} burst output #{filename_out}")

system returns a retrun code, the backtick-version return STDOUT.

If you need stdout and stderr, you may also use Open3.open3:

filename = 'filename.pdf'
filename_out = 'filename_%04d.pdf'
cmd = "pdftk #{filename} burst output #{filename_out}"

require 'open3'
Open3.popen3(cmd){ |stdin, stdout, stderr|
  puts "This is STDOUT of #{cmd}:"
  puts stdout.read
  puts "This is STDERR of #{cmd}:"
  puts stderr.read
}