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    Are you sure about point 2? The standard explicitly states "0 or more lines". So printf "a" > file would create a text file according to that definition. Your answer to 4 seems to be contradicting your answers to 2 and 5, as you suggest that touch file creates a text file while printf "a" > file does not. Commented May 27, 2018 at 11:31
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    @terdon: I don't see any contradiction in Michael's answer. Basically, he seems to be saying that a POSIX text file is any file whose contents matches the regexp (.{0,M}\n)* (implicitly anchored and both ends), where \n matches a newline and . matches any character that is not a newline, and M is a placeholder for the numeric value LINE_MAX-1. In particular, this implies that an empty file is a valid text file consisting of zero lines, but that any non-empty text file must end in a newline (since otherwise it would contain an incomplete line, and an incomplete line is not a line). Commented May 27, 2018 at 14:06
  • @Michael Homer Concerning the regular file thing, are there are other examples besides /dev/null? It's not really a text file since it contains one or more null characters. Commented May 27, 2018 at 18:20
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    @HaroldFischer /dev/null is an empty file. You’re thinking of /dev/zero. Commented May 27, 2018 at 19:10
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    @HaroldFischer, no, /dev/null reads as empty, as in you get no data when you read it. I'm not sure it makes much sense to consider non-regular files here, since of many of them are dynamic in nature. That includes pipes, sockets, char devices, which are basically just transport interfaces to/from some other entity. They don't hold any static set of data, so it'd make more sense to consider the properties of the data that was transferred, instead of the properties of the file. Commented May 27, 2018 at 19:21