A lesson in shortcuts. Long ago, as the design of the Unix file system was b...

A lesson in shortcuts.Long ago, as the design of the Unix file system was being worked out, the entries . and .. appeared, to make navigation easier. I'm not sure but I believe .. went in during the Version 2 rewrite, when the file system became hierarchical (it had a very different structure early on).  When one typed ls, however, these files appeared, so either Ken or Dennis added a simple test to the program. It was in assembler then, but the code in question was equivalent to something like this:   if (name[0] == '.') continue;This statement was a little shorter than what it should have been, which is   if (strcmp(name, ".") == 0 || strcmp(name, "..") == 0) continue;but hey, it was easy.Two things resulted.First, a bad precedent was set. A lot of other lazy programmers introduced bugs by making the same simplification. Actual files beginning with periods are often skipped when they should be counted.Second, and much worse, the idea of a "hidden" or "dot" file was created. As a consequence, more lazy programmers started dropping files into everyone's home directory. I don't have all that much stuff installed on the machine I'm using to type this, but my home directory has about a hundred dot files and I don't even know what most of them are or whether they're still needed. Every file name evaluation that goes through my home directory is slowed down by this accumulated sludge.I'm pretty sure the concept of a hidden file was an unintended consequence. It was certainly a mistake.How many bugs and wasted CPU cycles and instances of human frustration (not to mention bad design) have resulted from that one small shortcut about  40 years ago?Keep that in mind next time you want to cut a corner in your code.

(For those who object that dot files serve a purpose, I don't dispute that but counter that it's the files that serve the purpose, not the convention for their names. They could just as easily be in $HOME/cfg or $HOME/lib, which is what we did in Plan 9, which had no dot files. Lessons can be learned.)




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  • Jimmy Zelinskie's profile photo
    I was wondering why this post had so many comments. Then I found out it was posted on proggit/HN. The discussions there were hardly interesting, however.
  • Mark Lomas's profile photo
    $HOME/cfg and $HOME/lib are a terrible idea. They prevent you having two differently-configured instances of the same object within the same hierarchy (e.g. both owned by the same user). Actually I will go further, any absolute path that has special meaning makes it difficult to create two subtly-different instances of the same thing.How does Rob test an updated library without breaking the current instance? I hope he doesn't put the new version in $HOME/lib.

    Or to put it more succinctly, the '.' prefix allows me to have two or more instances of the same thing with the same name (by varying the parent folder). Absolute paths don't allow this.

  • K Kutani's profile photo
    +Mark Lomas Are you familiar with Plan 9's bind(1)?  It would solve the problems you posit.
  • Rob Pike's profile photo
    +Mark Lomas The . prefix doesn't do that, having a convention for a local configuration file does that. You can use a different convention.
  • Julius Schmidt (aiju)'s profile photo
    there is no feature so bad that some people won't love it.
    i could post examples but i don't want to cause any more flaming in this thread.
  • Rob Pike's profile photo
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