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Mac Forum / Programming / Perl / June 2006Odd 'head' problem
I'm not exactly sure this is what happened but I can't think of anything else. After installing several packages from CPAN, my daily log maintenance began failing. After some investigation I found that '/etc/periodic/daily/500.daily' was getting an error from the '/usr/ bin/head' command. When I ran 'head' manually the command was not the normal one. It appears that one of the perl packages replaced the normal 'head' command that works on files, with one that works on URLs. Has anyone encountered this, or can anyone determine if my surmise about one of the perl packages is correct? Thanks. Dennis Putnam Sr. IT Systems Administrator AIM Systems, Inc. 11675 Rainwater Dr., Suite 200 Alpharetta, GA 30004 Phone: 678-240-4112 Main Phone: 678-297-0700 FAX: 678-297-2666 or 770-576-1000 The information contained in this e-mail and any attachments is strictly confidential. If you are not the intended recipient, any use, dissemination, distribution, or duplication of any part of this e-mail or any attachment is prohibited. If you are not the intended recipient, please notify the sender by return e-mail and delete all copies, including the attachments. > I'm not exactly sure this is what happened but I can't think of > anything else. After installing several packages from CPAN, my [quoted text clipped - 6 lines] > anyone determine if my surmise about one of the perl packages is > correct? Thanks. This is a common gotcha on Os X. For some reason which I forget, but which I think was due to backwards compatibility with earlier versions of MacOs, the standard file system is not case sensitive: HEAD and head are considered equivalent. In the Perl distribution there is a script called "HEAD" which indeed does fetch the header of an HTML file from the web. This clashes with the standard Unix "head" command. There is a standard workaround, but just renaming the HEAD script solves things without (ISTR) breaking too much else. >> I'm not exactly sure this is what happened but I can't think of >> anything else. After installing several packages from CPAN, my [quoted text clipped - 8 lines] > > This is a common gotcha on Os X. No, it *was* a common gotcha, several years ago. > In the Perl distribution there is a script called "HEAD" which > indeed does fetch the header of an HTML file from the web. This > clashes with the standard Unix "head" command. It's in the LWP module, not the core Perl distribution. > There is a standard workaround Yes, it's called reading the instructions and paying attention. The current default behavior for LWP when installing on a case- insensitive is to *not* install the HEAD alias for lwp-request. That's been the default for quite a long time now - a couple of years at least. You have to specifically override the default for this to happen. sherm-- Cocoa programming in Perl: http://camelbones.sourceforge.net Hire me! My resume: http://www.dot-app.org You are (probably) correct. Its one of the web related cpan packages. LWP maybe, or something similar. It actually installs a command named HEAD rather than head, IIRC, but on a case insensitive file system, these are pretty much the same thing ... > I'm not exactly sure this is what happened but I can't think of > anything else. After installing several packages from CPAN, my [quoted text clipped - 21 lines] > intended recipient, please notify the sender by return e-mail and > delete all copies, including the attachments. > I'm not exactly sure this is what happened but I can't think of > anything else. After installing several packages from CPAN, my [quoted text clipped - 4 lines] > packages replaced the normal 'head' command that works on files, > with one that works on URLs. That's precisely what happened. The LWP package installs a script called HEAD that does an HTTP HEAD request. On case-insensitive file systems like HFS+, head and HEAD are the same. > Has anyone encountered this, or can anyone determine if my surmise > about one of the perl packages is correct? Thanks. Yes, many people have had this problem. It's not come up for several years, though, because recent versions of the LWP install script asks if you want to overwrite head and install HEAD when it detects a case- insensitive file system, and the default answer to that question is "no". Here's what the questions look like: The lwp-request program will use the name it is invoked with to determine what HTTP method to use. I can set up alias for the most common HTTP methods. These alias are also installed in /usr/bin. Do you want to install the GET alias? [n] Do you want to install the HEAD alias? [n] Do you want to install the POST alias? [n] The moral of the story - *read* the questions, don't just keep bouncing on the 'y' and 'return' keys. sherm-- Cocoa programming in Perl: http://camelbones.sourceforge.net Hire me! My resume: http://www.dot-app.org I don't recall those questions at all, however it is not at all obvious that 'HEAD' is going to replace 'head'. I'm not sure I understand the earlier comment about case insensitive filesystems. Certainly, OS X is not case insensitive at the CLI level, although 'Finder' is. However, PERL is running at the CLI level so I don't see why that should be a problem. Oh, well. Lesson learned, albeit too late. P.S. If 'HEAD' is an alias, where is the real file? >> I'm not exactly sure this is what happened but I can't think of >> anything else. After installing several packages from CPAN, my [quoted text clipped - 34 lines] > Cocoa programming in Perl: http://camelbones.sourceforge.net > Hire me! My resume: http://www.dot-app.org Dennis Putnam Sr. IT Systems Administrator AIM Systems, Inc. 11675 Rainwater Dr., Suite 200 Alpharetta, GA 30004 Phone: 678-240-4112 Main Phone: 678-297-0700 FAX: 678-297-2666 or 770-576-1000 The information contained in this e-mail and any attachments is strictly confidential. If you are not the intended recipient, any use, dissemination, distribution, or duplication of any part of this e-mail or any attachment is prohibited. If you are not the intended recipient, please notify the sender by return e-mail and delete all copies, including the attachments. > I don't recall those questions at all, however it is not at all > obvious that 'HEAD' is going to replace 'head'. I'm not sure I > understand the earlier comment about case insensitive filesystems. > Certainly, OS X is not case insensitive at the CLI level, although > 'Finder' is. That's complete nonsense, as the simplest test will show: ~ sherm$ echo "Hello world" > head ~ sherm$ cat HEAD Hello world HFS+ is a case-insensitive file system. Finder has nothing whatsoever to do with it - it's just a user-level file manager. sherm-- Cocoa programming in Perl: http://camelbones.sourceforge.net Hire me! My resume: http://www.dot-app.org >> I don't recall those questions at all, however it is not at all >> obvious that 'HEAD' is going to replace 'head'. I'm not sure I [quoted text clipped - 10 lines] > HFS+ is a case-insensitive file system. Finder has nothing > whatsoever to do with it - it's just a user-level file manager. base:~ me$ echo "hello Mac OS X mailing list" > head base:~ me $ cat HEAD cat: HEAD: No such file or directory base:~ me $ cat head hello Mac OS X mailing list base:~ me $ ;-) Yes, my boot volume is HFS+, and I have not moved the user directories off of it on this machine. Explanation: Case sensitivity is a property of the file system, which is separate from the shells (both CLI and GUI). Current versions of Mac OS X (from at least 10.2) allow you to specify case sensitivity on both UFS and HFS+ volumes when you partition a drive. I always format all my volumes case sensitive, except for the volume I keep classic on. I'm not sure if it's possible to change the case sensitivity when re- formatting existing partitions, and it would take more time than I want to take right now to check. As a side note, I prefer to put /usr/local, /www, and similar stuff on separate volumes formatted UFS as much as possible. Those are also case sensitive, of course. An even further off-topic complaint, it would be nice to be able to make an even finer cut, and put /var/log, /tmp, /var/tmp, etc. on separate partitions as damage-limiting measures, but, one, I run out of partitions when I do things like dual-boot openbsd, and, two, I won't trust Mac OS X's handling of hard or soft links to that level until /etc/fstab is respected before autodiskmount or whatever it's called kicks in. I've got swap on a separate partition on one of my old machines with limited hard disk space, and it definitely speeds that old machine up, but I don't recommend playing those tricks on a machine that I want to load arbitrary applications on. (Any Apple people reading the list, please note that there are good reasons for allowing /etc/fstab to do its job.) |
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