Why `wc -m` counts 1 character more?

Question

Why wc -m counts one character (symbol) more from here-string (<<<)

Here is example:

$ TEST_STR="askubuntu"
$ echo "$TEST_STR"
askubuntu
$ wc -m <<<"$TEST_STR"
10

It is saying 10, but actually there is only 9 symbols.

The same problem appears for wc -c

Answer 1

Because Bash Here strings add trailing newline character.

Here is proof:

$ TEST_STR="askubuntu"
$ echo "$TEST_STR"
askubuntu
$ od -c <<<"$TEST_STR"
0000000   a   s   k   u   b   u   n   t   u  \n
0000012

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Also, there is a few nice answers that explains why newline character should be there:

1. Why here string add newline character?
2. Why new line character should be there?