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Re: Simplifying code (Not obfuscation)

by zakb (Pilgrim)
on Mar 04, 2003 at 10:32 UTC ( #240285=note: print w/replies, xml ) Need Help??

in reply to Simplifying code (Not obfuscation)

In Perl, there's more than one way to do it, and your way is almost perfectly fine (by me).

First up, I would hope that you're using strict and warnings, and that $var is actually declared as my $var. This will help you in the future; see Why use strict/warnings for why.

The other improvement I would suggest is to lose the double quotes in your print statement if all you're printing is $var, i.e.:

print $var;

is sufficient.

One other thing you may want to do is check whether the system command actually executed successfully. The backquote returns undef if the command failed, and it would be good practice to check for this.

There are undoubtedly other things you can do, but with these suggestions and your code the way it is, it is understandable, readable and maintainable by anyone from a Perl novice to a god.

Update: added bit about checking return value of ``

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Re: Re: Simplifying code (Not obfuscation)
by 2mths (Beadle) on Mar 04, 2003 at 11:19 UTC
    A refreshing and totally unexpected tone of reply. I often see comments about more than one way..., but often there does seem to be a preferred way and/or a best practise way.

    I have already read the strict/warnings node and commented in agreement with it (My first post actually). I do use warnings but must admit that I don't tend to use strict. I'm trying to get myself into the habbit of doing so for 'production' code.

    In terms of testing the result of system would something like the below be appropriate?
    if ($var = `system thingy`) || die "Failed to get return from call to system\n";

    Thanks for the comments, encouragment and suggestions.

      Well for me, maintainability should be one of our highest concerns as developers: will the developer who follows me understand my code? But that's probably a good subject for a meditation later!

      You're close with catching the error; this should work:

      $var = `...` or die "System failed: $!\n";

      Basically, you don't need the if; the left hand side of the expression will be undef (false) if it fails, so the or will evaluate the right hand side. You'll see this form of error catching quite a bit, especially when using open and the like to operate on files. Note the use of $!, which will tell you what the system error message was - see perlvar for more information about this.

        Fantastic reply!

        Explanation of such things as: Use of if, or and $! greatly appreciated. One of those posts that makes brings together lots of snippets from here and there to create something far greater than the sum of it's parts.

        If I can vote for this reply I will, though it'll have to be tomorrow, my 5 for today have been spent.

      Your test is mixing two different kinds of conditional, the 'if' and the 'or' types.

      If/Unless version:

      unless ($var = `system thingy`) { die "Failed to get return from call to system\n"; }

      Or version:

      $var = `system thingy` or die "Failed to get return" from call to syst +em";
      Note the use of 'or' instead of ||. The only difference between them is their precendence, but as a result the 'or' doesn't need the braces round the assignment.

      Overall good coding style. Nice and readable. If all the code I had to do maintenance on was so readable I'd be a very happy bunny.

      Update: Changed the if to an unless since I totally messed up the logic. Oops. Thanks 2mths for pointing that out, shall try and engage brain earlier next time.

      Update: Fixed the missing ` problem. Thanks parv. Also updated brain to test all Perlmonks submissions to avoid silly mistakes like this in future.

        Again, a very welcome and highly appreciated post, highlighting to me the existance of and difference between "if" and "or".

        I won't pretend to understand the meaning of precedence in this context but I don't think that stops me understanding the pertinent points of your post.

        That said, looking closely at the if solution I would have thought that would die if the system call actually succeeded. Am I missing something?
        Molt, the unless version will not work due to missing "`" in the condition.

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