仅选择属于冒号的单词

我有一个使用标记语言的文本文件(类似于维基百科文章)

cat test.txt
This is a sample text having: colon in the text. and there is more [[in single or double: brackets]]. I need to select the first word only.
and second line with no [brackets] colon in it.

我需要选择单词“having:”仅仅因为这是常规文本的一部分。我试过了

grep -v '[*:*]' test.txt

这将正确避免标记,但不会选择预期的单词。