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Re^4: Parallelization of heterogenous (runs itself Fortran executables) code

by Dominus (Parson)
on Nov 21, 2007 at 22:13 UTC ( #652259=note: print w/ replies, xml ) Need Help??


in reply to Re^3: Parallelization of heterogenous (runs itself Fortran executables) code
in thread Parallelization of heterogenous (runs itself Fortran executables) code

Here is a version using Text::ParseWords and a modified spawn subroutine, which uses exec in scalar context.
I think that was an extremely bad move, because now you have to worry about shell metacharacters in arguments, which you formerly did not. For example, consider:
runN echo '*'
We are expecting this to run one echo to print out a star, but with your implementation, it does not; the quotes are stripped off and it echoes a list of the filenames in the current directory.

Similarly, suppose a file in the current directory is named foo bar. Then runN command * will run the command not with the argument foo bar but with the two arguments foo and bar.

Now let's suppose there is a file in the current directory named `rm -rf /`. (Note backquotes!) Then running your version of runN command * will erase the entire filesystem.

I wrote a blog entry about the perils of multiple shell evaluation in this context. I said:

My fear was that by introducing a double set of shell-like interpretation, I'd be opening a horrible can of escape character worms and weird errors, and my hope was that if I ignored the issue the problems might be simpler, and might never arise in practice.
This is exactly the sort of thing I was worried about. Your implementation certainly proves that I was correct about at least the first part of this prediction!


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