"We say that there is no reason to use --pedantic; it is just there to satisfy pedants who would otherwise say, "This isn't really an ANSI C compiler!"
Some GNU utilities such as df and du do not follow the POSIX spec unless you set the environment variable POSIXLY_CORRECT. Normally GNU df and du print disk space figures in units of k. POSIX says to print disk space figures in units of 512 bytes. If you set POSIXLY_CORRECT, GNU df and du do that. (My original plan was to name it POSIX_ME_HARDER.)"

Richard Stallman
interviewed by Federico Biancuzzi
at LinuxDevCenter
O'Reilly Network
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link Danny Yee