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fcntl 

        # IO.fcntl

(from ruby core)
---
    ios.fcntl(integer_cmd, arg)    -> integer

---

Provides a mechanism for issuing low-level commands to control or query
file-oriented I/O streams. Arguments and results are platform dependent.
If *arg* is a number, its value is passed directly. If it is a string,
it is interpreted as a binary sequence of bytes (Array#pack might be a
useful way to build this string). On Unix platforms, see `fcntl(2)` for
details.  Not implemented on all platforms.

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