how to write '@' in configure_file( "" @ONLY )

Code
1

how to write ‘@’ in configure_file( "@" @ONLY ) ?

input_file has the following content:

@

I tried configure_file( "input_file" @ONLY ) but am receiving \@.

2

I think the easiest solution is to create a CMake variable containing the at-sign and use it:

set(AT @)
configure_file("@AT@" @ONLY)