Only sysread returns characters as it receives them. read returns when the specified number of characters have been read, and readline returns when an end of line marker is found. (Reaching the end of file or encountering an error will have them return before that, of course.)

I forgot that <> reads lines (or more accurately, readline or glob, as you pointed out).

glob doesn't read files. I pointed out that <> can be a shortcut for glob, not that glob reads lines.