Programming Ruby: The Pragmatic Programmer's Guide

# Programming Ruby ### The Pragmatic Programmer's Guide
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module Errno

### Index:

Ruby exception objects are subclasses of `Exception`. However, operating systems typically report errors using plain integers. Module `Errno` is created dynamically to map these operating system errors to Ruby classes, with each error number generating its own subclass of `SystemCallError`. As the subclass is created in module `Errno`, its name will start `Errno::`.

The names of the `Errno` `::` classes depend on the environment in which Ruby runs. On a typical Unix or Windows platform, there are `Errno` classes such as `Errno::EACCES`, `Errno::EAGAIN`, `Errno::EINTR`, and so on.

The integer operating system error number corresponding to a particular error is available as the class constant `Errno::` error `::Errno`.

`Errno::EACCES::Errno` | » | `13`
`Errno::EAGAIN::Errno` | » | `11`
`Errno::EINTR::Errno` | » | `4`

The full list of operating system errors on your particular platform are available as the constants of `Errno`.

`Errno.constants` | » | `E2BIG, EACCES, EADDRINUSE, EADDRNOTAVAIL, EADV, EAFNOSUPPORT, EAGAIN, ...`

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
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