understanding $' ' quotes in bash

Question

At least in bash pattern substitution following quotes are often used: $' ' For example ${arr[@]/%/$'\n\n\n'} prints three newline characters after each array "arr" item. Are those some sort of special quotes? How are they called? Where are they used besides bash pattern substitution?

Answer 1

ANSI-C Quoting

Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard.

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For example:

$'hello\nworld'

You'll get 11 characters with newline in the middle.

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echo -e 'hello\nworld'
echo   $'hello\nworld'

They give you the same result.