Add Select A Specific Rails Version To Install as a Rails TIL

rails/select-a-specific-rails-version-to-install.md

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+# Select A Specific Rails Version To Install
+
+We can install a specific Rails version with `gem` using the version flag.
+
+```bash
+$ gem install rails --version 7.1.3
+```
+
+That's only if we already know which specific version we are intending to
+install.
+
+A better version of this would show us a list of available version and let us
+select the one we want.
+
+We can do this by fetching all remote Rails versions with `gem`, splitting that
+output up into a single version per line, and then piping that to an `fzf`
+prompt. The version we navigate to and select will be fed into the `gem
+install` command.
+
+```bash
+gem install rails --version $(
+  gem list rails --exact --remote --all \
+  | sed -n 's/.*(\([^)]*\)).*/\1/p' \
+  | tr ',' '\n' \
+  | sed 's/^ //' \
+  | fzf
+)
+```