Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

Re: mkdir in perldoc

by 7stud (Deacon)
on Jan 09, 2013 at 10:08 UTC ( #1012416=note: print w/replies, xml ) Need Help??

in reply to mkdir in perldoc

Perhaps because the names of files and directories are generically known as "filenames" in the unix world.

Replies are listed 'Best First'.
Re^2: mkdir in perldoc
by QM (Parson) on Jan 09, 2013 at 10:52 UTC
    Perhaps because the names of files and directories are generically known as "filenames" in the unix world.

    Not knocking you for this, but it's equivalent to Anonymous Monk's "Because", perhaps funneling into Appeal_to_tradition. But seriously, I understand, "FILENAME" here may be a generic term for any named filesystem entry, whether it's a file, link, directory, device, pipe, etc. But mkdir will only make directories, so let's be clear and specific, when that doesn't compromise generality. "mkdir DIRNAME" will in no way cause anyone to misunderstand what will happen.

    On the other hand, if there's some great savings in coding so docs and parsers and grammars don't have to handle special cases between things like chdir, mkdir, open, do, require, rmdir, chroot, link, symlink, and other things that take named filesystem entities, I'm all ears. I'm sure the developers have enough to do besides handle pedantic observations like this.

    Whoops! See rmdir:

        rmdir FILENAME
        Deletes the directory specified by FILENAME if that directory is empty. If it succeeds it returns true; otherwise it returns false and sets $! (errno). If FILENAME is omitted, uses $_ .
        To remove a directory tree recursively (rm -rf on Unix) look at the rmtree function of the File::Path module.

    And chmod and chown look weird, just specifying a list. For example:

        chmod LIST
    when the detail says the first element must be the mode. This is better written as:
        chmod MODE, LIST

    Quantum Mechanics: The dreams stuff is made of

      And chmod and chown look weird, just specifying a list. For example:

      chmod LIST

      when the detail says the first element must be the mode. This is better written as:

      chmod MODE, LIST

      Actually, the terse syntax examples given in the Perl documentation convey subtle meaning to those who are aware of the conventions being used and changing "chmod LIST" to "chmod MODE,LIST" would convey incorrect information to such people. (To become such a person, in part, one just needs to read, understand, and remember the 2nd paragraph of perlfunc.)

      $ say "prototype('CORE::chmod')" @

      I don't mind being told "mkdir FILENAME" because it hints at this possibility:

      $ perl -e'mkdir("$ENV{HOME}/.bashrc") or die $!,$/' File exists

      I started down the road of proposing that one of those conventions might actually be involved in the choice of "FILENAME" over "DIRNAME", because I noticed this:

      $ perldoc perlfunc | grep FILENAME | egrep '^ *[a-z]+ [A-Z]' chroot FILENAME mkdir FILENAME,MASK mkdir FILENAME rmdir FILENAME sysopen FILEHANDLE,FILENAME,MODE sysopen FILEHANDLE,FILENAME,MODE,PERMS $ say 'map prototype("CORE::$_"), qw/ chroot mkdir rmdir sysopen /' _ _;$ _ *$$;$

      But that doesn't make sense for a lot of reasons.

      I also noticed:

      $ perldoc perlfunc | grep DIRNAME $ perldoc perlfunc | grep FILENAME | wc -l 16

      So, how does opendir describe its argument?

      $ perldoc -f opendir | head -1 opendir DIRHANDLE,EXPR

      Now, that needs to say "DIRHANDLE" and not "FILEHANDLE", because you can't use a Perl DIRHANDLE as a Perl FILEHANDLE so that distinction is rather important. There is no such distinction between a FILENAME and a DIRNAME for Perl (nor for Unix, nor for Windows).

      But why is that "EXPR" and not "FILENAME"? Well, it is a common choice:

      $ perldoc perlfunc | egrep '^ {7}readlink [A-Z]' readlink EXPR $ perldoc perlfunc | egrep '^ {7}lstat [A-Z]' lstat EXPR $ perldoc perlfunc | egrep '^ {7}do [A-Z]' do BLOCK do SUBROUTINE(LIST) do EXPR Uses the value of EXPR as a filename and executes the c +ontents

      One could argue that "do EXPR" helps to convey the point that "any (other) expression gets interpretted as a file name" as opposed to possibly implying that Perl does something like looking at the value to see if it looks like a file name.

      [ I was surprised to (re)learn this:

      $ perl -we "do findModule(); sub findModule{''}" Use of "do" to call subroutines is deprecated at -e line 1.


      And that might explain the choice of "EXPR" for these cases as well:

      $ perldoc perlfunc | egrep '^ {7}truncate [A-Z]' truncate FILEHANDLE,LENGTH truncate EXPR,LENGTH $ perldoc perlfunc | egrep '^ {7}stat [A-Z]' stat FILEHANDLE stat EXPR stat DIRHANDLE

      Though, I think the case of noticing FILEHANDLE and DIRHANDLE exceptions really is about examining the value not about different syntax, so I find the "EXPR" choice less valuable here. But changing "stat EXPR" to "stat FILENAME" draws too much attention to the distinction between "FILE" and "DIR" in:


      While I think changing "DBNAME" to "FILENAME" would significantly improve the clarity here:

      $ perldoc perlfunc | egrep '^ {7}dbmopen [A-Z]' dbmopen HASH,DBNAME,MASK

      (Because "DBNAME" isn't a "FILENAME" in most contexts I deal with -- though, perhaps "FILENAME" was avoided since suffixes likely get appended.)

      How about places that don't use "EXPR"?

      $ perldoc perlfunc | egrep '^ {7}link ' link OLDFILE,NEWFILE $ perldoc perlfunc | egrep '^ {7}rename ' rename OLDNAME,NEWNAME

      I find "OLDNAME" a much better choice than "OLDFILE". Similar to the starting complaint, "OLDFILE" could be the name of a directory. But more important, for me, is that "OLDFILE" doesn't as clearly convey that what is given is the name of a file not some handle or other representation. I also wouldn't go more explicit like these:


      because I would worry about implying that these can't be used on directories [which isn't something I worry about implying for mkdir() or rmdir()]. One could argue for:


      but I'd probably depart even further and go with:


      (I've long found the argument order for link,3 and ln quite confusing, I must admit.)

      After considering the broader context, I think most of the uses of "FILENAME" really should be changed to "DIRNAME". Not because I find those uses of "FILENAME" confusing or inappropriate, but because they are cases where the distinction doesn't matter and so "DIRNAME" is just slightly clearer. (I find many cases that are a lot more in need of improvement than the one that started this thread.)

      Contrast that with changing "lstat EXPR" to "lstat FILENAME". I don't like "lstat FILENAME" as it sounds like it might be trying to imply that you can't use it on directories or links, but only on plain files. But I also see no reason to use "EXPR" for that case. I think I prefer "lstat PATHNAME".

      So my updates would only be as follows:

      So I'd explicitly leave these unchanged:


      - tye        

        Thank you for an excellent exposition. This is exactly the kind of discussion I was hoping for.

        I agree with almost everything you say (and I'll only be slightly annoying by replying further).

        In several cases, such as stat, I would prefer something more generic than FILENAME. Something that conveys FILESYSTEMENTITY, but that doesn't work. I can't come up with anything better.

        In the other direction, some uses of EXPR seem almost lazy by comparison. Once the concept that an expression can be evaluated into a value or list, the docs don't need to use EXPR much. Where it's clear and simple, I'd go for a more descriptive term, such as your lstat PATHNAME example. I especially like localtime EPOCHSECONDS.

        I still don't like chmod LIST, because the first element is distinctly different from the rest. chmod MODE, LIST seems much clearer and more descriptive. In most cases LIST is about as useful as EXPR, if only slightly better in conveying multiple values are possible.

        (Aside: I wish module synopses were on average clearer, as in many cases I have to read deeper to find out that it was easier than the first read.)

        Quantum Mechanics: The dreams stuff is made of

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1012416]
beech testing in the sidebar
beech *me* me *me

How do I use this? | Other CB clients
Other Users?
Others taking refuge in the Monastery: (4)
As of 2017-03-28 23:37 GMT
Find Nodes?
    Voting Booth?
    Should Pluto Get Its Planethood Back?

    Results (343 votes). Check out past polls.