Collect prints to a string

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

Replies are listed 'Best First'.
Re: Collect prints to a string by toolic (Bishop) on Apr 23, 2011 at 18:46 UTC
One way to effectively buffer your print output is to open a filehandle directly to a scalar variable, then select the filehandle. Then you can print to STDOUT at a later time. This allows you to avoid modifying your sub. The following snippet is UNTESTED: `my $out; open my $fh, '>', \$out or die "cant open variable\n"; select $fh; print1('foo'); # do some stuff print STDOUT $out;` [download]	[reply] [d/l]
Re: Collect prints to a string by wind (Priest) on Apr 23, 2011 at 19:14 UTC
As documented in open `use strict; use warnings; open my $fh, '>', \my $buffer or die "Can't open memory file: $!"; select $fh; foo(); bar(); print STDOUT "<buffered>\n$buffer</buffered>\n"; sub foo { print "Hello from Foo\n"; } sub bar { print "Hello from Bar\n"; } __END__` [download] Update: Removed unnecessary reference to `my $stdout = \*STDOUT;` Thanks toolic.	[reply] [d/l] [select]
Re: Collect prints to a string by InfiniteSilence (Curate) on Apr 23, 2011 at 17:58 UTC
Step 1: Learn to write tests in Perl and create a separate test for every function that you plan to modify. Make certain that all tests pass 100% before proceeding. [ Contextual note: I add this because, when making changes to production code, you can avoid the fear of breaking things by having comprehensive testing available to run automated regression tests. Once you get used to doing this you will lose your fear of refactoring production code.] Step 2: Change the offending function names by appending something to them. So `sub print_l` becomes `sub print_l_old`. Change the 'print' statements to 'return' statements. Rerun your tests. Everything should break (that's okay for now). Step 3: Create new functions with the old function names and have them call the old functions like this: `use strict; sub print_l_old { return qq\|the world is a great place\|; } sub print_l{ print print_l_old() . qq\| to be.\|; } print_l();` [download] The idea of a function is normally to return something. In other languages there is a way to notify the user whether or not a function was supposed to be used to return anything (like declaring it void, etc.). There is not anything like this in Perl (that I know of) so my best practice is to almost always write functions to return something, even if that something is only `undef`. Whatever solution you come up with, I would add it to your coding standards. I added this section and all this help about refactoring because I think the code you have posted probably needs to be rewritten. There are good, safe ways to do that using Perl utilities. Update: Oops, I forgot to mention that your tests will break if you add new stuff like `qq\| to be.\|`. The right approach should be to just call the old functions in the new without appending anything and rerun your tests. They should all pass. Then rewrite your tests to match your next version's changes. You should be using a version control system, so you should be able to easily differentiate versions and tag releases along with associated tests. Celebrate Intellectual Diversity	[reply] [d/l] [select]
Re: Collect prints to a string by mikeraz (Friar) on Apr 23, 2011 at 17:34 UTC
You mean something like: `sub print_1 { my $text = shift; return <<EOT; <p> $text </p> <form> form stuff </form> EOT }` [download] ??? Be Appropriate && Follow Your Curiosity	[reply] [d/l]
Re^2: Collect prints to a string by vit (Friar) on Apr 23, 2011 at 17:46 UTC
"return" will need to modify subs which I do not want to do. Probably I do not even need to write return because a default return will work, like $string .= print_1($text); ?	[reply]