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Fixing Unix/Linux/POSIX Filenames

Mar 26, 2009, 13:02 (0 Talkback[s])
(Other stories by David A. Wheeler)

"A Tale of Complications
magine that you don't know Unix/Linux/POSIX (I presume you really do), and that you're trying to do some simple things with it. For example, let's try to print out the contents of all files in the current directory, putting it into a file above:

cat * > ../collection

"The list doesn't include "hidden" files (filenames beginning with "."), but often that's what you want anyway, so that's not unreasonable. The problem is that although this usually works, filenames could begin with "-" (e.g., "-n"). So if there's a file named "-n", and you're using GNU cat, all of a sudden your output will be numbered! Oops; that means on every command we have to disable option processing; for most commands that means using "--" everywhere, except not all commands support "--" (ugh!). There are lots of traps, e.g., for portability you're supposed to use printf(1) not echo(1) if the first parameter might start with a "-". Many people know that prefixing the filename or glob with "./" can resolve these kinds of problems (e.g., "cat ./*"), and most versions of "find" do prefix filenames by default. But not all programs do such prefixing, because it's not immediately obvious that you need to do so. As a result, when you're writing a new program, you can't guarantee that the caller has prefixed it nicely for you."

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