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Calling external programs

Rusty Shackleford
Ranch Hand

Joined: Jan 03, 2006
Posts: 490
I am writing a series of scripts that run and use output from a variety of network tools. What tools and what arguments will be determined at runtime, and these arguments can get complex. For example running nmap -PA -sV -O -T4 -p80,443,8080,8443,9000-10000 <target>. If the target and arguments are know before running it, it is simple, either use `...` or %x{...}, but this method seems to not take string parameters only literals, using system makes it impossible to capture output which is what I need to do. I am using open3 which works but doesn't seem to be ideal. I would like to have to be free from constructing the complete command line string, but this is the only thing that seems to work.

If I try:
inp,out,err = popen3(@tool, @args)
inp.puts @target
It works with one argument, but not multiple. This would be perfect because I will likely have a list of targets, but arguments may change based on other runtime criteria. The problem is that this only works with 1 argument, passing in multiple arguments as either a single string or many arguments results in failure: either a broken pipe or nmap can't see the target. So my solution is to build a single string and pass that:

inp,out,err = popen3(@tool)

Where @tool is something like 'nmap -PA -sV -O -T4 -p80,443,8080,8443,9000-10000 <target>'. Is there a better way to accomplish this? This works but having to build a lot strings during runtime is going to slow things down considerably as I may have hundreds of targets and a dozen or more tools to run and parse data from.

"Computer science is no more about computers than astronomy is about telescopes" - Edsger Dijkstra
Bear Bibeault
Author and ninkuma

Joined: Jan 10, 2002
Posts: 62275

"Rusty Shackeford", please check your private messages for an important administrative matter.

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Lasse Koskela

Joined: Jan 23, 2002
Posts: 11962
You can use #{} for string interpolation within %x[] statements like this:

Author of Test Driven (2007) and Effective Unit Testing (2013) [Blog] [HowToAskQuestionsOnJavaRanch]
I agree. Here's the link:
subject: Calling external programs