[texhax] Issue about `~' character

[David Carlisle]

Your question is very unclear.

you say you can not use \string~ as it occurs within a \write
but \string~ will work within a write and cause ~ to be written as itself
as a ~ to the file.

If you are inputting that file back to TeX then you also need to make
that ~ that you
read back in to be inert there are various ways to do that, depending
what you are doing
you could for instance do

\write\wherever{\string\string\string~}

which will write

 \string~

to the file which if \input back will produce

~

David