You can seek any seekable filehandle, including STDIN, but only if it's seekable. {grin}

It depends on what it's opened on. If it's a terminal or a pipe or a socket, no. If it's a file, yes (usually). The easiest way is to try, and note the success/failure result from seek, and then interpret $! on failure.

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.