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Open3.popen3

As explained in The Well-Grounded Rubyist, Fourth Edition

Open3.popen3 is a Ruby method that starts an external program and returns separate handles for its standard input, standard output, and standard error.

Open3.popen3 starts an external program and returns separate handles for its standard input, standard output, and standard error. Require the open3 library first; unlike the Ruby session's own streams, these handles communicate directly with the child process. section 14.6.2

A cat session

require 'open3'\nstdin, stdout, stderr = Open3.popen3("cat")\nstdin.puts("Hi.\\nBye")\nstdout.gets # => "Hi.\\n"\nstdout.gets # => "Bye\\n"

The returned values support a deliberately separated communication model:

  • Write data to the input handle and read the child process's output through the output handle. section 14.6.2
  • Capture errors independently through the error handle, while a fourth return value provides a Process::Waiter object that can be ignored in simple cases. section 14.6.2

How The Well-Grounded Rubyist, Fourth Edition covers it

How deep it goes
Demonstrates basic stream exchange and threaded interaction but stops short of deeply treating system-level behavior.
Examples
Uses cat sessions, line-based input and output, and a threaded program that groups every three responses.
What it assumes
Requires loading the open3 library and working with Ruby I/O handles; the examples establish the separate process streams directly.
What you can do after
Operate an external program from Ruby by writing to its input and reading its output and errors through separate handles.
How it connects
Connects external programs with standard streams, I/O handles, threads, and process waiting.
Cover of The Well-Grounded Rubyist, Fourth Edition
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of The Well-Grounded Rubyist, Fourth Edition. The section links point to the parts of the book it draws on.