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Re^4: true from (-e "") on Windoze (" is an illegal filename character

by ikegami (Pope)
on Sep 17, 2012 at 05:34 UTC ( #993968=note: print w/ replies, xml ) Need Help??


in reply to Re^3: true from (-e "") on Windoze (" is an illegal filename character
in thread true from (-e "") on Windoze

Not sure why "yuck"?

Either, it should be treated as illegal and return "The system cannot find the file specified",

It's an invalid file name, so it should return an error indicating such. It doesn't, thus "yuck".


Comment on Re^4: true from (-e "") on Windoze (" is an illegal filename character
Re^5: true from (-e "") on Windoze (" is an illegal filename character
by BrowserUk (Pope) on Sep 17, 2012 at 06:30 UTC
    It's an invalid file name, so it should return an error indicating such.

    Not so.

    When you type "" on the command line, the program never sees the "s as they are processed by the command line processor. What the program receives is an empty string.

    In a very (perlish) pragmatic manner, the OS chooses to use what would otherwise be a nonsensical value -- to which even an error message of "Illegal filename" would be wrong, because strictly, they haven't supplied any file name -- to have a meta meaning and utilises it.

    In this case, it would be nonsensical to dir/stat files matching 'nothing', so it ascribes that value the meta meaning -- a default value -- of 'everything'.(*)

    That is no different to many perl built-ins using $_ if they receive no parameters. Or *nix taking a bare ls to mean everything. (The fact that they issue an "No such file or directory" message to ls '' is both strictly wrong; and missing a trick.)

    Pure pragmatism of the kind that Perl does so well.

    Whilst I could understand -- but disagree with -- a Java programmer saying yuck to such pragmatism, it strikes me as disjoint coming from a Perl aficionado like you.

    * It is even logical at the CS level, in that, the empty string is a vaild substring of every possible string.)


    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

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      I was talking about -e '""' (a system call), not dir "" (a command line tool). What's appropriate for one is not necessarily appropriate for the other.

      That said, I'm not convinced the behaviour of dir "" is the best. Note that ls "" returns ls: cannot access : No such file or directory.

        I was talking about -e '""' (a system call), not dir ""... What's appropriate for one is not necessarily appropriate for the other.

        The system call that underlies dir is the same system call that underlies -e, thus similar behaviour is entirely appropriate.

        Making them different would be the wrong thing to do.

        I'm not convinced the behaviour of dir "" is the best.

        Convinced or not; best or not; it is the behaviour, for better or worse.

        Making Perl work differently would be as asinine as truncating 32-bit return codes to 8-bits. (Whatever happened to the the principle of maximum information preservation)

        The principle of least surprise dictates that you don't screw with the heads of developers on a given platform, in order to accommodate the expectations of programmers cross-targeting it from other platforms.

        Note that ls "" returns ls: cannot access : No such file or directory.

        The fact that *nix has an anything goes policy to filename characters, doesn't make it a good idea.

        Think of all the extra code written/maintained to accommodate for/protect against all the accidental/malicious possibilities that policy creates

        But, I doubt we'll ever agree, so let's agree to differ.


        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.

        RIP Neil Armstrong

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