chore(kb): start notes about output redirection

knowledge base/redirect outputs.md

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+# Redirect outputs
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+
+## TL;DR
+
+Pipes are set up **before** the I/O redirections are interpreted.<br/>
+The sequence of I/O redirections is interpreted **left-to-right**.
+
+```sh
+command 2>&1 >'/dev/null' | grep 'something'
+command 2>'/dev/stdout' 1>'/dev/null' | grep 'something'
+
+# Swap the standard error and standard output over, then close the spare descriptor used for the swap.
+command 3>&1 1>&2 2>&3 3>&-
+```
+
+## Further readings
+
+- [How can I pipe stderr, and not stdout?]
+- [Pipe only STDERR through a filter]
+- [File Descriptors in Bourne shell]
+
+<!--
+  Reference
+  ═╬═Time══
+  -->
+
+<!-- Others -->
+[File Descriptors in Bourne shell]: https://mixedvolume.blogspot.com/2004/12/file-descriptors-in-bourne-shell.html
+[How can I pipe stderr, and not stdout?]: https://stackoverflow.com/questions/2342826/how-can-i-pipe-stderr-and-not-stdout
+[Pipe only STDERR through a filter]: https://stackoverflow.com/questions/3618078/pipe-only-stderr-through-a-filter#52575087