From: brian d foy <brian.d.foy@gmail.com>
Date: Sat, 21 Aug 2010 15:47:37 +0000 (-0500)
Subject: * How can I write() into a string?
X-Git-Tag: v5.13.5~67
X-Git-Url: https://perl5.git.perl.org/perl5.git/commitdiff_plain/3cd7ab715194be8ea797d7f907f547c571ec12f2

* How can I write() into a string?
	+ Actually answer the question, now that we have
	filehandles to strings.
	+ The swrite in perlform is no good anyway.
---

diff --git a/pod/perlfaq5.pod b/pod/perlfaq5.pod
index bd969f4..683910e 100644
--- a/pod/perlfaq5.pod
+++ b/pod/perlfaq5.pod
@@ -644,7 +644,54 @@ techniques to make it possible for the intrepid hacker.
 =head2 How can I write() into a string?
 X<write, into a string>
 
-See L<perlform/"Accessing Formatting Internals"> for an C<swrite()> function.
+(contributed by brian d foy)
+
+If you want to C<write> into a string, you just have to <open> a 
+filehandle to a string, which Perl has been able to do since Perl 5.6:
+
+	open FH, '>', \my $string;
+	write( FH );
+	
+Since you want to be a good programmer, you probably want to use a lexical
+filehandle, even though formats are designed to work with bareword filehandles
+since the default format names take the filehandle name. However, you can 
+control this with some Perl special per-filehandle variables: C<$^>, which
+names the top-of-page format, and C<$~> which shows the line format. You have
+to change the default filehandle to set these variables:
+
+	open my($fh), '>', \my $string;
+	
+	{ # set per-filehandle variables
+	my $old_fh = select( $fh );
+	$~ = 'ANIMAL';
+	$^ = 'ANIMAL_TOP';
+	select( $old_fh );
+	}
+
+	format ANIMAL_TOP =
+	 ID  Type    Name
+	.
+	
+	format ANIMAL =
+	@##   @<<<    @<<<<<<<<<<<<<<
+	$id,  $type,  $name
+	.
+
+Although write can work with lexical or package variables, whatever variables
+you use have to scope in the format. That most likely means you'll want to 
+localize some package variables:
+
+	{
+	local( $id, $type, $name ) = qw( 12 cat Buster );
+	write( $fh );
+	}
+	
+	print $string;
+
+There are also some tricks that you can play with C<formline> and the 
+accumulator variable C<$^A>, but you lose a lot of the value of formats
+since C<formline> won't handle paging and so on. You end up reimplementing
+formats when you use them.
 
 =head2 How can I open a filehandle to a string?
 X<string> X<open> X<IO::String> X<filehandle>