Regex to replace $vars with subroutine

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

I created an HTML page I need to get my script to work with. I decided the easiest way would be to drop $var placeholders in my code where I want each of the "active content" to load into. I have $galleryname, $gallerypictures, etc as placeholders.

Now when I get($page) via LWP::Simple, how do I then s/$var/ with the results of a subroutine? Each placeholder has their own subroutine to determine what will be printed in that section.

$page =~ s/\$galleryname/&galleryname/;
[download]

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Re: Regex to replace $vars with subroutine by friedo (Prior) on Jun 06, 2008 at 19:53 UTC
The proper way to do this is with one of the many templating modules that exist on CPAN, such as HTML::Template. But if you truly want to roll your own, you can use the /e option on your regex (see perlre) to make the replacement string executable code.	[reply]
Re: Regex to replace $vars with subroutine by Corion (Patriarch) on Jun 06, 2008 at 20:05 UTC
All you're missing is the `/e` modifier, see perlre. `$page =~ s/\$galleryname/galleryname()/ge` [download]	[reply] [d/l] [select]
Re^2: Regex to replace $vars with subroutine by Anonymous Monk on Jun 06, 2008 at 23:06 UTC
Hi. Can you see why this isn't working as expected? `use warnings; use strict; my $string = "this is a test \$placeholder"; $string =~ s/\$placeholder/test_sub()/e; print $string; sub test_sub { print "hello there"; }` [download] # prints "hello therethis is a test1 I don't want the subroutine to print anything, just do everything it needs to do and print out all output back into the $string	[reply] [d/l]
Re^3: Regex to replace $vars with subroutine by kyle (Abbot) on Jun 07, 2008 at 01:19 UTC
Change print to return, and it works. `use warnings; use strict; my $string = "this is a test \$placeholder"; $string =~ s/\$placeholder/test_sub()/e; print $string; sub test_sub { return "hello there"; }` [download] If you really need to capture the output of what a sub `print`s, that's a whole other problem. I was doing something like that in Use of uninitialized value in open second time but not first., and there's more discussion with it about other ways to do it.	[reply] [d/l] [select]
Re: Regex to replace $vars with subroutine by kyle (Abbot) on Jun 06, 2008 at 21:51 UTC
I agree with friedo. A template is the right way to go. The solution from Corion will work fine, but you may also want to look at How do I avoid double substitution when replacing many patterns?	[reply]
Re: Regex to replace $vars with subroutine by Narveson (Chaplain) on Jun 06, 2008 at 19:58 UTC
Update: Put `$page` through two passes of string interpolation. `$galleryname = galleryname(); $page = eval "qq{$page}";` [download] It struck me right away that your `$var` placeholders are just begging to be interpolated. If `gallery()` returns `'the Rijksmuseum'` and `$page` is `'Welcome to $gallery!'`, then `eval` will see `qq{Welcome to $gallery}` and `$page` will get `'Welcome to the Rijksmuseum!'`	[reply] [d/l] [select]