Help using Benchmark.pm

Ovid has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to verify some regex optimizations, so I decided to benchmark my code.

#!/usr/bin/perl -w 
use strict; 

my $myvar = 'Tom said "hi," and Sally replied "get lost, Ovid is more 
+my style."';

use Benchmark;
 timethese(100000, { 
    Greedy  => '$myvar =~ /"(.*)"/', 
    Lazy    => '$myvar =~ /"(.*?)"/', 
    Negated => '$myvar =~ /"[^"]*"/' 
});
[download]

Unfortunately, the above code keeps giving me the following error:

Use of uninitialized value at (eval 2) line 1.
[download]

I've tried swapping out the single quotes, the double quotes, and even tried running the debugger on it (yeah, I know that must do wonders for timing your code). I've also read up on a fair amount of documentation for this, all to no avail! Help

Thanks in advance for any advice!

Cheers,
Ovid

Comment on Help using Benchmark.pm Select or Download Code

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RE: Help using Benchmark.pm by autark (Friar) on Jul 12, 2000 at 23:02 UTC
Hi, Your problem can be solved by making $myvar a global, either by using: `use vars qw\|$myvar\|; $myvar = "...";` [download] or if you use perl 5.6: `our $myvar = "...";` [download] It can also be solved by letting the keys in that hash point to functions: `timethese(100000, { Greedy => sub { $myvar =~ /"(.)"/ }, Lazy => sub { $myvar =~ /"(.?)"/ }, Negated => sub { $myvar =~ /"[^"]*"/ } });` [download] If the value of one of the keys is not a reference to a function, Benchmark is forced to eval your code - and when you eval a string all the variables referenced within it will be looked up in the stash (where all the symbols live) - they are treated as globals you could say. That's why it works when you make $myvar a non-lexical variable. Autark.	[reply] [d/l] [select]
Re: Help using Benchmark.pm by btrott (Parson) on Jul 12, 2000 at 22:59 UTC
`use vars qw/$myvar/;` [download] No my. Don't declare it as lexical, because it won't be in scope when you're actually running the benchmarked code. Or rather when Benchmark is running your code.	[reply] [d/l]
RE: Help using Benchmark.pm by Adam (Vicar) on Jul 12, 2000 at 22:53 UTC
You need to give `$myvar` a value in each snippet. `Greedy => '$myvar =~ /"(.)"/',` becomes `Greedy => '$myvar = "Some String"; $myvar =~ /"(.)"/',` For more advice see the node Benchmarking Your Code. Update: I see that I located the problem (scoping), but not the cause.(the `my`)	[reply]
RE: Help using Benchmark.pm by Ovid (Cardinal) on Jul 12, 2000 at 23:14 UTC
Thanks for the help everyone! It's now running just fine :)	[reply]