bash: ANSI C quoting

In bash, $'...' quoting (aka "ANSI C quoting", aka "dollared single quoting") is a special type of quoting that expands use of ANSI C-style escape characters.

For comparison, here are unquoted, single quoted (literal), double quoted (mainly literal), and ANSI C quoted (escapes expanded) examples:

echo hi\tbye     # hitbye
echo "hi\tbye"   # hitbye
echo 'hi\tbye'   # hitbye
echo $'hi\tbye'  # hi(tab)bye

See bash manual page on ANSI C Quoting