Add Create Multi-Line Strings Without The Line Breaks as a yaml til

yaml/create-multi-line-strings-without-the-line-breaks.md

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+# Create Multi-Line Strings Without The Line Breaks
+
+There are [many ways](https://stackoverflow.com/a/21699210/535590) to add
+multi-line strings to a YAML document. Most of them preserve the literal
+newlines present in the multi-line string. And generally that is what you want
+in a multi-line string.
+
+Sometimes, however, you want a multi-line string just for its readability in
+the file. The literal representation of the string should exclude the newlines.
+To achieve this, you can use either `>-` or `|-`.
+
+```yaml
+run: >-
+  echo "::set-output name=NODE_VERSION::$(
+    cat .tool-versions
+    | grep nodejs
+    | sed 's/nodejs \(.*\)$/\1/'
+  )"
+```
+
+This creates a readable key-value pair without introducing newline characters
+into the string that represents a shell command.