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• Network vulnerability and port scanning services

  - by DigitalRoss

  I'm setting up a periodic port scan and vulnerability scan for a medium-sized network implementing a customer-facing web application. The hosts run CentOS 5.4. I've used tools like Nmap and OpenVAS, but our firewall rules have special cases for connections originating from our own facilities and servers, so really the scan should be done from the outside. Rather than set up a VPS or EC2 server and configuring it with various tools, it seems like this could just be contracted out to a port and vulnerability scanning service. If they do it professionally they may be more up to date than something I set up and let run for a year... Any recommendations or experience doing this?

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• Is there a bash shortcut for traversing similar directory structures?

  - by Steve Weet

  The Korn shell used to have a very useful option to cd for traversing similar directory structures e.g. given the following directorys /home/sweet/dev/projects/trunk/projecta/app/models /home/andy/dev/projects/trunk/projecta/app/models Then if you were in the /home/sweet.... directory then you could change to the equivalent directory in andy's structure by typing cd sweet andy So if ksh saw 2 arguments then it would scan the current directory path for the first value, replace it with the second and cd there. Is anyone aware of similar functionality in bash. EDIT 1 Following on from Michal's excellent answer I have now created the following bash function called scd (For Sideways cd) function scd { cd "${PWD/$1/$2}" } EDIT 2 Thanks to @digitalross I can now reproduce the ksh functionality exactly with the code from below (With the addition of a pwd to tell you where you have changed to) cd () { if [ "x$2" != x ]; then builtin cd ${PWD/$1/$2} pwd else builtin cd "$@" fi }

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• I'm having a problem identifying a floating point exception.

  - by Peter Stewart

  I'm using c++ in visual studio express to generate random expression trees for use in a genetic algorithm type of program. Because they are random, the trees often generate (I'll call them exceptions, I'm not sure what they are) Thanks to a suggestion by George, I turned the mask _MCW_EM on so that hardware interrupts are turned off. (the default) So, the program runs uninterrupted, but some of the values returned are: -1.#INF, -1.#NAN, -1.#INV. I don't know how to identify these so that I can throw an exeption: if ( variable == -1.#INF) ?? DigitalRoss in this post seemed to have the solution, but as I understood it I couldn't make it work. I've been looking all over the place for this simple bit of code, that I assumed would be used all the time, but have had no luck. thanks

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• Why no more macro languages?

  - by Muhammad Alkarouri

  In this answer to a previous question of mine about scripting languages suitability as shells, DigitalRoss identifies the difference between the macro languages and the "parsed typed" languages in terms of string treatment as the main reason that scripting languages are not suitable for shell purposes. Macro languages include nroff and m4 for example. What are the design decisions (or compromises) needed to create a macro programming language? And why are most of the mainstream languages parsed rather than macro? This very similar question (and the accepted answer) covers fairly well why the parsed typed languages, take C for example, suffer from the use of macros. I believe my question here covers different grounds: Macro languages or those working on a textual level are not wholly failures. Arguably, they include bash, Tcl and other shell languages. And they work in a specific niche such as shells as explained in my links above. Even m4 had a fairly long time of success, and some of the web template languages can be regarded as macro languages. It is quite possible that macros and parsed typing do not go well together and that is why macros "break" common languages. In the answer to the linked question, a macro like #define TWO 1+1 would have been covered by the common rules of the language rather than conflicting with those of the host language. And issues like "macros are not typed" and "code doesn't compile" are not relevant in the context of a language designed as untyped and interpreted with little concern for efficiency. The question about the design decisions needed to create a macro language pertain to a hobby project which I am currently working on on designing a new shell. Taking the previous question in context would clarify the difference between adding macros to a parsed language and my objective. I hope the clarification shows that the question linked doesn't cover this question, which is two parts: If I want to create a macro language (for a shell or a web template, for example), what limitations and compromises (and guidelines, if exist) need to be done? (Probably answerable by a link or reference) Why have no macro languages succeed in becoming mainstream except in particular niches? What makes typed languages successful in large programming, while "stringly-typed" languages succeed in shells and one-liner like environments?

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