i am new in linux and using ubuntu'10.10'...i basically want to know as what is the significance of learning shell....????...i googled but max time i find tutorial but didnot get any satisfactory answers...
Whenever you want to automate small tasks where using real programming languages is overkill (e.g. batch convert files, rip DVD chapters, synchronize directories, ...) shell scripts often are invaluable.
Moreover, a lot of "plumbing" in the system is done with shell scripts (e.g. daemons start/stop scripts, event scripts), so knowing at least how to read them often can give you a grasp on how some parts of the system work under the hood, and give you a clue about where the problem can lie in case of malfunctions; knowing how to write them can also be useful if you need to customize the system in some way.
That is a nice question to ask. The fact is that studying shell script help you to do a lot of tasks, (well it helped me ). I used shell script whenever i had to perform more than one Linux commands one by one and sometimes when I had to run jobs over and over again with same pattern. Shell really helps in doing such tasks.
And off the syllabus, studying shell for tasks made me more familiar with the OS and commands.
Related
Does anyone know of a scripting language that's included with most platforms (say Mac/Windows/Linux)? I haven't been able to find one. So far javascript in web browsers or compiled java are about it. Jython comes close.
My goal is to be able to download a file from the web or portable storage and just run it, without having to install something first, or have special user permissions, or edit it, or rename it, or give it executable privilages. It would give you access to generally accepted metaphors in computing: input, output, persistent storage, time, spawning tasks, sockets, fixed and floating point math, unicode, etc. Ideally it would abstract away minutia like line endings, endianness, and yielding for other processes.
I don't want to get into why having a universal language/virtual machine is important, or at the very least, useful. I feel that we are missing a middleware above the operating system level, something like POSIX but less esoteric, and without it, we all are forced to spend a disproportionate amount of time reinventing the wheel or writing special cases. For me, availability and a complete feature set are more important than speed (which could come later).
Thanks in advance for any insights you can provide,
Zack Morris
You will be able to run carefully written sh scripts on almost all unix systems.
If you want to add Microsoft systems, then it is more difficult, but still possible to provide a single script file, that will "autodetect" the interpreter it's running on and select between a sh part and a command.com or whatever they have on Microsoft systems.
Once you can run a script on a known system you can further download or unpack and install automatically whatever software you need.
I am working on a solution for which I need a work flow/process flow engine. My work flow contains some Java based processes(classes) and some Linux Shell scripts. The flow would not be static and the execution of each process depends on the state/outcome of the previous process, and there would be multiple paths and the path would be determined the state of the previous processes.
I tried looking at jBPM, but I do not find a suitable support for invoking shell scripts. Please suggest me a suitable alternative for my requirement.
Many thanks.
well you can use jBPM5, it's extremely simple to add support for running shell scripts, we can help you with that.
Can you elaborate a little bit more on the requirements that you have?
Cheers
I'm trying to automate input into a command line C program (which I have no control over), it takes arguments, runs some processor intensive code (read takes a minute), then prompts to fill out form like information. I'm not sure what the best way to Input into the prompts once they become available. Are there any CPAN libraries which make this easier? How should I go about this? To clarify I'm trying to wrap this program as a library. Kind of like how Git::Wrapper Wraps git.
Without knowing more about the program you're trying to automate, I'd suggest you start by looking at Expect. It's also possible to do this with IPC::Run's start, pump, and finish functions, but Expect is a higher-level module. (And for a really low-level module, there's IPC::Open3 in core.)
Question
What would be a good (ideally, technical) reason to ever program some non-trivial task in dos batch language on a modern Windows system as opposed to downloading either PowerShell, or ActiveState Perl?
To be more specific, I make the following two assumptions for the duration of this question:
anyone technical enough to be able to write a medium-complexity batch script is technical enough to install either of the scripting interpreters.
Neither of those two present enough of a learning curve for basic batch replacement tasks that said curve would outweigh the pain of doing any remotely-non-trivial task in batch.
Notes
"You need a batch program for autoexec.bat" is not a valid reason. Your autoexec.bat may consist of simply calling non-batch script.
If you disagree with either of my 2 assumptions above, that's fine, and I may be wrong. But my question is specifically "assuming those 2 assumptions are correct, what would be the reason to still stick with batch?" If it makes it easier to suspend disbelief (in case you disagree with me), add in a 3rd assumption that the question is limited to people who already posess at least some modicum of PowerShell or Perl experience.
To re-iterate - this is not meant to be a subjective question about how easy it is to learn PSh or ASPerl compared to doing advanced batch coding. That is a separate question that is too subjective to be bothered with in this post.
Background:
I used to do some fairly complicated batch programming back in the elder days, and remember batch as one of the worst possible programming languages I had encountered.
The idea for this question came after seeing a bunch of batch questions on SO, and trying to grok the answer of one of them out of sheer curiosity and giving up in pain after a minute, exclaiming mentally "why would anyone go through this pain instead of doing that in 1 line of Perl?" :)
My own plausible answer
I assume there may be an an likely DOS-compatible system, which has DOS interpreter but has no compatible PowerShell or Perl... I'm not aware of one but not completely impossible.
Typically, the rationale is that you need the script to run on a machine which does not have another interpreter and on which you are not allowed to install an interpreter. Production servers in many companies are a good example -- you want them to have as few exploitation vectors as possible, which means no scripting languages that are not required for application functionality.
You're right when you say that the batch language is a terrible language -- there's a reason they sunk the time and money into building PowerShell -- but it's also the only universal language you can rely on across the myriad versions of Windows.
Because I work at a bank where the default browser is IE6 on Windows XP and I have no idea if I'll be able to install PowerShell on someone's computer and I have a batch file which they can use to quickly and easily:
sqlcmd with some pre-import SQL
bcp
sqlcmd with some post-import SQL
With the whole batch needing to be RUNAS /NETONLY because the workstation does not participate in the domain that the SQL Server is on/trusts.
Not that I'm complaining or anything...
And I would say they are non-trivial because sometimes they take parameters and they require some pretty crazy escape quoting.
I have a contract at a major utility company which absolutely does not allow unapproved programs on their computers. That would be expected of computers attached to the innermost networks which connect between control computers and devices, but the ban applies to the general purpose and administrative networks too.
The approved operating system is Windows XP SP3 with IE6. Upgrading is not allowed until technical support blesses it. Which, it seems, still may be some years from now.
Therefore, batch files are the only general scripting tool available. Some developer machines have access to C++ compilers, but the resulting programs are not permitted for internal distribution until the conclusion of a (probable multi-year) validation effort.
You could also choose to use vbscript or jscript rather than perl and you wouldn't need to worry about installing any additional software.
various reasons
Its company policy, be it for security or other illogical reasons given by management, that you strictly
use DOS.
You had to support some legacy DOS
scripts already written.
You or the admins in the company
only know DOS and have no capacity
to learn other languages.
You are coding for part of a larger
DOS program already written
Doing things the "harder" way make you look
cool.
You have a lot of time on your hands
to devise workarounds for some
things that are difficult to do
easily with DOS
I package our server releases into zip files using a batch file (Windows), running the command-line version of WinZip. Previously we did this sort of thing "by hand" but I developed the process of automating it with a batch file.
The batch file has become quite complicated because our product is complicated (i.e., Which sections are we releasing this time? Are we releasing the config files as well?) and I'm starting to run into some frustrating limitations with batch files.
Would PowerShell be a good thing to investigate as an "upgrade" to the batch file? Or is that complete overkill given that most of what it would be doing is firing off DOS commands?
Bonus: can PowerShell consume .NET assemblies? As in, could I start doing the zipping with SharpZip?
If you have a working solution, then you don't need to go to powershell. Having said that, if you plan to make changes or improve the process then I would highly recommend powershell as the way to go. Powershell can access .Net assemblies...mostly. Some assemblies are structured in a way that makes it more difficult than others.
You can check here for some resources if you decide to look at powershell.
Initially I was really excited about PowerShell. Finally a powerful native shell on Windows. However, I quickly realized that compared to your favorite unix shell PowerShell is just way too verbose. Even doing simple stuff takes way too much typing compared to what you can do with bash and GNU tools for Win32.
I like the idea, that the shell knows about different types, but if I need to do that much additional work, I prefer just getting the necessary data with the various unix stream editors.
EDIT: I just had another look at PowerShell, and I have to admit, that it does have some really useful features that are not available for the traditional unix style tools.
For one the PowerShell owns all the commands which means that it can provide a much more coherent set of features. Parameters are treated uniformly, you can search for commands, parameters and so forth using wild cards which is really useful.
The second great feature is that PowerShell lets you enumerate sources which are normally not available to stream editors such as the Windows registry, the certificate store and so forth. Of course you can have tools that does this for you and present it as text, but the PowerShell approach is just really elegant IMO.
Take a look at PowerShell Community Extensions (PSCX), its FREE and it has Zip cmdlets:
Write-Zip
Write-BZip2
Write-GZip
http://www.codeplex.com/PowerShellCX
You should watch this presentation/discussion with Jeffrey Snover, PowerShell creator and architect. If you're not amazed by the technical details (lots of "wow" moments to be had), you'll be amazed by Jeffrey's enthusiasm :). Once you get the basics, it's easy to be very productive with PowerShell.
The answer is YES - PowerShell can use .NET assemblies. There is a bit of funny business involved in v1 if you need to wire up delegates and v2 makes that much more clean.
Just call LoadFile / LoadAssembly to get the appropriate libraries in memory and away you go
[Reflection.Assembly]::LoadFile('/path/to/sharpzip.dll')
$zip = new-object ICSharpCode.SharpZipLib.Zip.FastZip
$zip.CreateZip('C:\Sample.zip', 'C:\BuildFiles\', 'true', '^au')
# note - I didn't actually test this code
# I don't have SharpZip downloaded - just read their reference.
Also note that the PowerShell Community Extensions support various compression methods like write-zip.
I've tried to replace one of the lengthy build batch files I use with power shell. I found it a pain: at least at that time, documentation focused on the funny verbiage and what cool, perly things you can do with it, but lacked in the "getting simple things done" category. I got it working, but the error handling was to shaky.
YMMV, try powershell, you might enjoy it. But try it before updating your build batches.
My solution: use a C# console application. I've got serious logging, exception handling, can use my utility functions, and if something doesn't work I have a real debugger. It's the first solution I like to modify.
I'm not sure about powershell, but might I recommend using something like IronPython (if you want to have access to the .NET libraries) or plain python? You get a full-blown programming language with very few limitations.
On the one hand, if it works, just leave it. But it sounds like this is something you'll be adding to over time, and of course your eventual successor/coworker who needs to edit the batch file will also need to understand it. If you're from a programming background then you may well find the power of Powershell makes your script a lot shorter and easier to read/maintain (for example, even just having full if statements and for/while loops). On the other hand if you're not overly familiar with programming, a lot of people find Powershell a bit daunting at first glance.
Regarding the .NET part, Powershell is built on top of .NET so yes, you can access .NET assemblies (but you should always see if there's a cmdlet available first).
I would recommend a book called "The Powershell Cookbook" by Lee Holmes, published by O'Reilly. It provides "recipes" which you can use for common tasks; this will probably speed up your time to implement the script, and it'll teach you Powershell along the way.