What does this param expansion do?

Question

What exactly does the following do?

MY_VAR=${MY_INPUT##*$'\n'}

Answer 1

Deletes the longest match of the substring *\n from the start of the string stored in MY_INPUT. Note that * is a wildcard, so the result is that every line of MY_INPUT is discarded except the last one, which is stored in MY_VAR. The $ before '\n' is put there just to evaluate \n and consider it as a newline instead of literally the characters \ and n.

Some examples:

MY_INPUT            MY_VAR
"a\nb\nc"        -> "c"
"a\n"            -> ""
"abcde\n\n\ndef" -> "def"

Note: in the second example the last line is empty so MY_VAR is an empty string.

---

As requested, another way to do this could be:

tail -n1 <<< "$MY_INPUT"

or:

echo "$MY_INPUT" | tail -n1