You need the format_write and format_top_name methods (and maybe others, depending on how sophisticated your form handling needs to be). IO::Tee inherits some format-handling code from IO::Handle. The docs for IO::Tee really only mention it in passing, but it becomes clearer in the docs for IO::Handle, and you need to be sure to tell IO::Tee specifically about things like which format to use for top-of-form (which is "automatic" for STDOUT and the like).

The following code snippet should get you started. Notice that since the name of the format is passed down to IO::Tee, you need to specify the full package name of the format (o/wise you get complaints about undefined formats from IO::Tee). 

use strict;
use warnings;
use IO::Tee;

my( $abc, $xyz ) = ( q/hello/, 12345 );

format TEE_TOP =
==== Top of Output ====
.

format TEE =
@<<<<<  @#####
$abc,   $xyz
.

# with lexical file handle; can also use bareword handle
open my $outfile, '>', 'junk.out'  or die "error opening junk.out: ($!
+)";
my $tee = IO::Tee->new( \*STDOUT, $outfile );

# see docs for IO::Tee and IO::Handle for explanation of these methods
# and others available for proper format use/control
$tee->format_top_name( q/main::TEE_TOP/ );
$tee->format_write( q/main::TEE/ );

[download]
From the shell:

-> ./tst-tee-write
==== Top of Output ====
hello    12345
-> cat junk.out
==== Top of Output ====
hello    12345

[download]

In reply to Re: IO::Tee and write / format by broomduster
in thread IO::Tee and write / format by beadon

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.