ANSI-C Quoting (Bash Reference Manual)

3.1.2.4 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. Backslash escape sequences, if present, are decoded as follows:

\a: alert (bell)
\b: backspace
\e

\E

an escape character (not ANSI C)
\f: form feed
\n: newline
\r: carriage return
\t: horizontal tab
\v: vertical tab
\\: backslash
\': single quote
\": double quote
\?: question mark
\nnn: the eight-bit character whose value is the octal value nnn (one to three octal digits)
\xHH: the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
\uHHHH: the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
\UHHHHHHHH: the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
\cx: a control-x character

The expanded result is single-quoted, as if the dollar sign had not been present.