Can't save console output as Ruby variable

Question

I am having trouble saving the output of a command in console into Ruby as a variable. I am trying to save information of a .p12 file in as a variable p12_info. This is what I have tried so far.

file = File.read("certificate.p12")
p12 = OpenSSL::PKCS12.new(file, "")
p12_info = `openssl pkcs12 -in #{p} -info -noout -passin pass:""`
print "Info: "
puts p12_info

And this is the output I'm getting:

File name: certificate.p12
MAC Iteration 1
MAC verified OK
PKCS7 Encrypted data: pbeWithSHA1And40BitRC2-CBC, Iteration 2048
Certificate bag
Certificate bag
PKCS7 Data
Shrouded Keybag: pbeWithSHA1And3-KeyTripleDES-CBC, Iteration 2048
Shrouded Keybag: pbeWithSHA1And3-KeyTripleDES-CBC, Iteration 2048
Info:

The console command seems to be running when I try to set the variable p_12, but doesn't actually get saved into p12_info.

Alternatively if I try this:

p12_info = `echo "foo`
print "Info: "
puts p12_info

Then I get this output, which is what Im going for:

File name: certificate.p12
Info: foo

Any ideas about why this could be happening will be greatly appreciated.

EDIT:

@tadman - Thanks so much for the help. You are correct, the command did in fact output with the appended > /dev/null. Unfortunately, I am having trouble figuring out how to use popen3. I am very unfamiliar with all this..I've tried:

Open3.popen3(`openssl pkcs12 -in bad_certificate.p12 -info -noout -passin pass:""`) {|stdin, stdout, stderr, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  p12_info = wait_thr.stderr # Process::Status object returned.
}

To no avail. Any pointers that could lead me in the right direction? Much appreciated.

Are you sure the output is going to STDOUT? You can test on the shell with openssl ... > /dev/null and if you still see output then it's writing to STDERR instead. Then you'll have to use popen3. — tadman
– tadman, Commented Jul 23, 2013 at 15:16
Is that what you put for the popen3 call? It should be in regular quotes, not back-ticks. — lurker
– lurker, Commented Jul 23, 2013 at 16:54
@mbratch yeah, that was a mistake. tadman pointed me in the right direction, but nevertheless, many thanks for the input — Anthony To
– Anthony To, Commented Jul 23, 2013 at 17:33

tadman · Accepted Answer · 2013-07-23 16:59:15Z

1

You're missing a few things. One is that popen3 takes a string argument, and backticks cause an external shell call that coincidentally returns a string.

The backtick convention comes from the bash shell where it's used to inline the result of a command:

ls -l `which ls`

This could expand to:

ls -l '/bin/ls'

With that in mind, what you should have is this:

Open3.popen3('openssl pkcs12 -in bad_certificate.p12 -info -noout -passin pass:""') do |stdin, stdout, stderr, wait_thr|
  # stderr is a standard IO filehandle
  p12_info = stderr.read
end

answered Jul 23, 2013 at 16:59

tadman

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