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Fault Tolerant Shell
Paul Howe writes "Roaming around my school's computer science webserver I ran across what struck me as a great (and very prescient) idea: a fault tolerant scripting language. This makes a lot of sense when programming in environments that are almost fundamentally unstable i.e. distributed systems etc. I'm not sure how active this project is, but its clear that this is an idea whose time has come. Fault Tolerant Shell."
It's a well meaning idea, but it would cause more problems than it would solve. It would just encourage sloppy code; people would rationalize "I don't need to fix errors because it doesn't matter", which is a very bad habit to get into when programming, ignoring errors, or even warnings
a auto-completing python interpreter and editor
Try the Wing IDE. It has most of the functions you wanted... But it's not free software.
The right to offend is far more important than the right not to be offended. (Rowan Atkinson)
This will not improve people's skills. In fact, it willl make them more prone to mistakes, and more likely to get the result that they didn't expect. It's similat to computer spell checkers. Ever since people started relying on these, their spelling has gone way downhill simly because they don't bother thinking. Computer do all the spelling for them. They don;t need a spell checker. They need spelling lessons.
This si even worse. Computers will try to second guess what the user means, get get it wrong half tyhe time.
A qualified shell scripter will be not make these mistakes in the first place. Anyone who thinks they need this shell actually just need to learn to spell and to ytype accuratly.
While, yes, you manage distributed systems from the center, you don't *push* updates, changes, modifications because, it doesn't scale. You end up having to write stuff like this fault tolerant shell which is frankly backwards thinking.
Instead, you automate everything and *pull* updates, changes, scripts etc. That way if a system is up, it just works, if it's down, it'll get updated next time it's up.
I won't go into details but I'll point you at http://infrastructures.org/
Government of the people, by corporate executives, for corporate profits.
how many times have you hacked something together in perl that ended up being relied on for some pretty important stuff, only to find 6 months down the track that there's some condition (db connects fine, but fails halfway through script execution as an example) you didn't consider and the whole thing just collapses in a heap - a nasty to recover heap cause you didn't write much logging code either.
This would REALLY be useful when you're connecting to services external to yourself - network glitches cause more problems with my code than ANYTHING else, and it's a pain in the arse to write code to deal with it gracefully. i'd really really like to see a universal "try this for 5 minutes" wrapper, which, if it still failed, you'd only have one exit condition to worry about. hey, what the hell, maybe i'll spend a few days and write one myself.
Perhaps the answer to the problem of teenagers dropping bricks from motorway and railway bridges is to sue Tetris.
All the programmers who need the environment to compensate for their inadequacies, step on one side. All the programmers who want to learn from their mistakes and become better at their craft, get on the other side.
Most of us know where this line is located.
So what happens if the files are crucial (let's use the toy example of kernel modules being updated): The modules get deleted, then the update fails because the remote host is down. Presumably the shell can't rollback the changes a la DBMS, as that would involve either hooks into the FS or every file util ever written.
Now I think it's a nice idea, but it could easily lead to such sloppy coding; if your shell automatically tries, backs off and cleans up, why would people bother doing it the 'correct' way and downloading the new files before removing the old ones?
Doesn't that depend on the definition of clustered though? Clustered systems can be things like beowulf clusters. But often a collection of standalone web servers behind a http load balancers is commonly referred to as a web cluster or array.
IMHO as someone who works in a complex web server / database server environment, there are many interdependancies brought by different software, different platforms and different applications. Whilst 100% uptime on all servers is a nice to have, it's a complex goal to achieve and requires not just expertise in the operating systems & web / database server software but an indepth understanding of the applications.
A system such as this fault tolerant shell is actually quite a neat idea. It allows for flexibility in system performance and availability, without requiring complex (and therefore possibly error prone or difficult to maintain) management jobs. An example would be server which replicates images using rsync. If one of the targets is busy serving web pages or running another application, ftsh would allow for that kind of unforeseen error to be catered for relatively easily.
The Romans didn't find algebra very challenging, because X was always 10
You obviously didn't read the article.
"It [ftsh] is especially useful in building distributed systems, where failures are common, making timeouts, retry, and alternation necessary techniques."
It doesn't protect you from typos in the script, it handles failures in the commands that are executed.
I'm sorry, but I can't understand why a Windows port (even if not native) is even attempted. Seems kind of useless in a totally GUI environment. Of course, maybe it's just me?
-- There is no spoon. Only fork.
Shell scripts should be short and easy to write. I have seen plenty of them fail due to some resource or another being temporarily down. At first people are neat and then send an email to notify the admin. When this then results in a ton of emails everytime some dodo knocks out the DNS they turn it off and forget about it.
Every scripting language has their own special little niche. BASH for simple things, perl for heavy text manipulation, PHP for creating HTML output. This scripting language is pretty much like BASH but takes failure as given. The example shows clearly how it works. Instead of ending up with PERL like scripts to catch all the possible errors you add two lines and you got a wonderfull small script, wich is what shell scripts should be, that is none the less capable of recovering from an error. This script will simply retry when someone knocks out the DNS again.
This new language will not catch your errors. It will catch other peoples errors. Sure a really good programmer can do this himself. A really good programmer can also create his own libraries. Most find of us in admin jobs find it easier to use somebody elses code rather then constantly reinvent the wheel.
MMO Quests are like orgasms:
You may solo them, I prefer them in a group.
"An example would be server which replicates images using rsync. If one of the targets is busy serving web pages or running another application, ftsh would allow for that kind of unforeseen error to be catered for relatively easily."
It depends how you organise your systems. If you push to them then yes you need something like ftsh. If you organise them so that they pull updates, pull scripts to execute and arrange those scripts so that they fail safe (as they all should anyway) then you'll have something which is a couple of orders of magnitude more reliable and scalable. It just needs a little more thought to begin with.
Government of the people, by corporate executives, for corporate profits.
Well that was just an example. If on the other hand the system the images were pulled from was very busy then the same is true. The problem is that you can't architect for a moving target and the flexbility that rapidly changing environments require is something which ftsh would be quite useful for.
The Romans didn't find algebra very challenging, because X was always 10
Comment removed based on user account deletion
Here's a Ruby one:
def college_try (limit, seq =0)
begin
yield
catch e
# forgot the syntax for getting the block
college_try( limit, seq + 1, block ) if (seq < limit)
end
end
college_try( 50 ) {
begin
do some work
catch e
do error clean up here
raise e
ensure
do cleanup that should always run here
end
}
Anyways, I agree with the notion that most popular scripting languages have advanced error handling that is up to the task.
Ofcourse bash can do it as well using the proper constructions. That is not the point. Care should be taken not to view bash as a golden hammer when it comes to shell scripting. The same goes for 'ftsh', ofcourse. It won't try to replace bash for every script out there.
The author merely thinks it would be nice to have a shell in which such fault-tolerant constructions are natural by design. Just to save people headaches when writing simple scripts which are there to get some job done, not to waste time dealing with every single possible failure and time-out by hand.
I could more damage with "wile true; do ... " in bash. It's not like an infinite loop is very hard. ftsh on the other hand defaults to exponential backoff, which isn't exactly what you want if you want to DOS someone.
Resources DO become unavailable in most systems. It simply doesn't pay to ensure everything is duplicated, and set up infrastructures that makes it transparent to the end user - there are almost always cheaper ways of meeting your business goals by looking at what level of fault tolerance you actually need.
For most people hours, sometimes even days, of outages can be tolerable for many of their systems, and minutes mostly not noticeable if the tools can handle it. The cost difference in providing a system where unavailabilities are treated as a normal, acceptable condition within some parameters, and one where failures are made transparent to the user can be astronomical.
To this date, I have NEVER seen a computer system that would come close to the transparency you are suggesting, simply beause for most "normal" uses it doesn't make economic sense.
> Your example only does a fraction
> of what ftsh does.
yawn, so we didn't post a 100-500 line library in our slashdot comment.
the point is, this stuff would be trivial to implement in language like ruby. plus, using a full scripting language you get lots of other useful features like regular expressions, classes, etc, etc
It's a good idea, but it's a library implemented as a language.
Spell checkers are *not* a substitute for knowing how words are spelled.
Of course not. But using a spell checker means having time to learn about the homonyms, instead of endlessly playing catch up.
You still predicated your post on "relying" on spell checkers; I'm saying that people learn from good spell checkers. That people can't learn everything from a spell checker is hardly a reason to throw the baby out with the bath water and insist that people use inferior learning techniques anyhow!
A kid that can spell accurately is in a much better position to learn about homonyms then one for whom spelling is still a mysterious, abstract art that involves guessing at things.
What's with all of the people claiming that FTSH will ruin the world because it makes it easier to be a sloppy programmer. Did you freaking read the documentation?
To massively oversimplify, FTSH adds exceptions to shell scripting. Is that really so horrible? Is of line-after-line of "if [$? -eq 0] then" really an improvement? Welcome to the 1980's, we've discovered that programming languages should try and minimize the amount of time you spent typing the same thing over and over again. Human beings are bad at repetitive behavior, avoid repetition if you can.
Similarlly FTSH provides looping constructs to simplify the common case of "Try until it works, or until some timer or counter runs out." Less programmer time wasted coding Yet Another Loop, less opportunities for a stupid slip-up while coding that loop.
If you're so bothered by the possibility of people ignoring return codes it should please you to know that FTSH forces you to appreciate that return codes are very uncertain things. Did diff return 1 because the files are different, or because the linker failed to find a required library? Ultimately all you can say is that diff failed.
Christ, did C++ and Java get this sort of reaming early on? "How horrible, exceptions mean that you don't have to check return codes at every single level."
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