Placement of $~ or $FORMAT_NAME

[loris]

Dear All,

I know I should be using Perl6::Form and not struggling with Perl5 formats, but bear with me.

I want to print something formatted to the terminal or to a file. This is what I came up with:

#!/usr/bin/perl

use strict;
use warnings;
use English qw( -no_match_vars );

use Getopt::Long;

my $file;
my $file_name = 'delete_me.txt';

GetOptions('file|f' => \$file,
          );

my $greeting = "Hello World!";

format BLAH =
Greeting: @<<<<<<<<<<<<<<<<
$greeting
.

$FORMAT_NAME = "BLAH";

my $fh;

if (defined($file)) {
    open($fh,'>',$file_name) or die "Couldn't open $file_name for writ
+ing: $!";
    select($fh);
}

#$FORMAT_NAME = "BLAH";
write();

if (defined($file)) {
    close($fh);
}

The code above produces the error

Undefined format "$fh" called at ./test.pl line 32.

if called with ./test.pl -f. If I uncomment the line before the write(), the data is written to the file.

Why is this and is there a better idiom for switching between filehandles when using formats?

Thanks,

loris

[JavaFan]

From the documenation:

       HANDLE->format_name(EXPR)
       $FORMAT_NAME
       $~      The name of the current report format for the currently
               selected output channel.  Default is the name of the
               filehandle.  (Mnemonic: brother to $^.)

You change the default filehandle after initially setting $FORMAT_NAME.

[loris]

Ah, so $~ isn't set for whichever filehandle is current, but just for the one that is current at the moment. If I change the filehandle with select() I also have to reset $~.

Thanks,

loris

[Tux]

Take care when switching: also $: and $^A can be affected and $%, $=, $-, and $^ will change on a select. The values might not always be reliable :) YMMV