move dir fundamentals to basics

basics/shell.md

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+# Shells
+
+Dash - fast but limited funcionality, great for scripts.
+
+sh - primitive and ubiquitous.
+
+bash - the standard
+
+elvish - user-friendly, but new, with a full file-browser embedded into the system.
+
+# Login
+
+All shells launch either as login or non-login.  All remote sessions without a GUI withl require authentication, and therefore will be login.
+
+## Login
+
+These shells start by reading /etc/profile then the first of ~/.bash_profile, ~/.bash_login or ~/.profile, and load all given values.
+
+## Non-Login
+
+Non-login shells will read /etc/bash.bashrc and then the ~/.bashrc file.  You can summon the different shell perameters with the command `.`.
+
+For example, so summon the file ~/.bashrc, you can perform:
+
+`. ~/.bashrc`
+
+How the logout is handled depends upon ~/.bash_logout
+
+# Defaults
+
+The default shell config files to create for a new user are under /etc/skel.
+
+# Shellcheck
+
+Run `shellcheck script.sh` on your scripts to check them for mistakes.
+