Output to a file. ! allows an existing file to be overwritten even if noclobber is set. & redirects both stdout and stderr.

Append to a file

Read stdin from a file

Inline data: the text on the following lines, up to the line containing only the specified string will be fed as stdin to the statement. Command and variable substitution is normally done on the inline text.

In the special case where string contains any of the quoting characters, ^ ', " or `, they're discarded without processing. But both the resulting string and the inline text are taken as literal text.