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Re: feeding text to a process, and capturing its output, safely

by QM (Vicar)
on Mar 23, 2004 at 19:49 UTC ( #339149=note: print w/ replies, xml ) Need Help??


in reply to feeding text to a process, and capturing its output, safely

Can you comment on the "safely" aspect of this?

-QM
--
Quantum Mechanics: The dreams stuff is made of


Comment on Re: feeding text to a process, and capturing its output, safely
•Re: Re: feeding text to a process, and capturing its output, safely
by merlyn (Sage) on Mar 23, 2004 at 19:52 UTC
    Yes.

    Oh, you mean will I elaborate?

    OK.

    No shell is involved. This makes it safer than the solutions I've seen that usually end up as something like:

    my @RESULT = `echo $INPUT | Some Command`;
    The problem is that $INPUT is being handed to a shell, making me have to worry and wonder about all shell-sensitive characters.

    -- Randal L. Schwartz, Perl hacker
    Be sure to read my standard disclaimer if this is a reply.

      Thanks, I had forgotten about that.

      I should think this method might be preferred then, unless the application is something quick-and-dirty.

      Will you please comment on the disadvantages of this method?

      -QM
      --
      Quantum Mechanics: The dreams stuff is made of

        Will you please comment on the disadvantages of this method?

        It depends on where your input is coming from and what it contains, but in the general case, wherein the input *might* contain shell metacharacters and *might* potentially even be constructed with malice, the shell *might* give complete control of your system (or, at least, as much control as is available to the user the code is running as) to whoever constructed the input. More likely, however, a shell metacharacter will get included randomly by someone who is not aware of the implications and cause apparently random breakage. For example, you'll put an ampersand in the input one time without thinking, and Weird Stuff(TM) will happen, and you'll have to track down the problem and figure out that the ampersand needs to be escaped, and so on. This is bad: your program is not robust, and input that's a little different from what was anticipated causes it to unexpectedly fail.

        It's also something of a portability nightmare, since different shells have different metacharacters that behave in different ways. This can create all kinds of zany debugging fun.


        ;$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}} split//,".rekcah lreP rehtona tsuJ";$\=$;[-1]->();print

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