grep
find

[Unix] Find files contains string

 find . -name *.yml -exec grep -l '\[\]' {} \;

Explanation:

find . -name *.yml 

Find the files with extension of yml;

-exec ..

Select if the command exit code is zero value after exec.

grep -l 

Output file path inside of content.

{}

File path pass from find as a parameter of grep

\;

The -exec must end with ;, if invoke from shell must with quote \;.