Add Define Multiline Strings With Heredocs as a Ruby TIL

ruby/define-multiline-strings-with-heredocs.md

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+# Define Multiline Strings With Heredocs
+
+[A _heredoc_ (_here document_) is a special ruby
+syntax](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Here+Documents)
+for defining formatted multiline strings. These are useful for any situation
+where you need to define a block of text where newlines and indentation are
+preserved -- e.g. output an error, help message, or some formatted SQL.
+
+The standard syntax is defined with `<<` and some uppercase identifier (e.g.
+`TXT`, `DOC`, `SQL`, etc.) to open and close the multiline string.
+
+```ruby
+def lookup_team(team_id)
+  query = <<SQL
+    select users.id from users
+      join teams
+        on teams.id = users.team_id
+      where teams.id = #{team_id}
+      order by created_at desc
+      limit 10;
+SQL
+
+  team_member_ids = db.execute(query)
+end
+```
+
+With the SQL formatted this way, it is easier to read and we can print/log out
+this nicely formatted version to make debugging easier.
+
+Notice that the terminating `SQL` identifier is fully left justified. I find
+that visually off relative to the indentation of everything else, so I like to
+use the _indented_ heredoc syntax (`<<-`).
+
+```ruby
+def lookup_team(team_id)
+  query = <<-SQL
+    select users.id from users
+      join teams
+        on teams.id = users.team_id
+      where teams.id = #{team_id}
+      order by created_at desc
+      limit 10;
+  SQL
+
+  team_member_ids = db.execute(query)
+end
+```