reverse the order of characters in a string

Question

In string \"12345\", out string \"54321\". Preferably without third party tools and regex.

Answer 1

rev | tail -r (BSD) or rev | tac (GNU) also reverse lines:

$ rev <<< $'12\n34' | tail -r
43
21
$ rev <<< $'12\n34' | gtac
43
21

If LC_CTYPE is C, rev reverses the bytes of multibyte characters:

$ LC_CTYPE=C rev <<< あの
��め�
$ export LC_ALL=C; LC_ALL=en_US.UTF-8 rev <<< あの
のあ