How expensive is: require "foo.pl";

I'm about to rewrite a large portion of a project that I have developed over the last 10years while learning perl. There is alot of optimisation that can be gained.

A key part of the code is a large if/elsif block that require xxx.cgi files depending on a POST value. Eg:

    if($FORM{'action'} eq "1"){require "1.cgi";}
elsif($FORM{'action'} eq "2"){require "2.cgi";}
elsif($FORM{'action'} eq "3"){require "3.cgi";}
elsif($FORM{'action'} eq "4"){require "4.cgi";}

It has many more irritations but开发者_Go百科 just how expensive is using "require" in perl?

require itself has a relatively low cost in any case and, if you require the same file more than once within a single run of your program, it will detect that the file has already been loaded and not attempt to load it a second time. However, if you have a long and highly-populated search path (@INC) and you require (or use) a lot of files, it's possible that all of the directory searches could add up; this isn't common (and doesn't sound likely in your case), but it can be improved by reorganizing your module directories so that the things you're loading show up earlier in @INC.

The potentially-major performance hit referred to by earlier answers is the cost of compiling the code in the files you require. Getting rid of the require by moving the code into your main program will not help with this, as the code will still need to be compiled. In your case, it would probably make things worse, as it would cause the code for all options to be compiled on every one rather than only compiling the code used by the one action selected by the user.

As has been said, it really depends on the actual code in those files. Your best bet would be to do tests using Devel::NYTProf and/or Benchmark to see where the most time is being spent in your code if you are unhappy with its performance.

You can also read Profiling Perl on perl.com, but it is a bit outdated as it uses Devel::DProf.

Not answer to your primary question, but still a good idea for code refactor i read recently in Ovid blog.

The first time, possibly expensive; Perl has to search a path to find the file and load it up. Subsequent times, it's cheap -- a table is consulted and the file isn't actually loaded a second time. If this is in a CGI that is run once per request and then exited, then this is not too good.

It's really going to depend on the size of the files you're calling to. If you have massive CGI files, then it might detriment the performance of your software. If we're talking 6 or 7 lines of code each, then no issue. Try benchmarking your program's performance with and without, and make your own judgement.