The quotes are important because of what they do: Without them, the shell catches the pipe before the shell you're invoking (cmd.exe) even sees them.
Without quotes: 
{ C:\Windows\System32\cmd.exe /c c:\test\slowproc.cmd } | tee.exe proc
+esslog

[download]
with quotes (hopefully): 
C:\Windows\System32\cmd.exe /c { " c:\test\slowproc.cmd | tee.exe proc
+esslog " }

[download]
If you could get rid of the call to tee.exe, you could get rid of using cmd.exe too. Much as I dislike it when a monk rashly suggests the OP turn left after requesting help with turning right, here goes:

Instead of the cmd.exe/tee.exe adventure, have you considered using Perl's fork(), then in the child process: open CMD, "slowproc.cmd|";? You could then write anything you get on <CMD> to STDOUT and a log file. (OK, my Camel is at work, so I'm hoping that I did that right from memory. I will trust the other monks to gently correct if not.)

If you're not interested in going down the fork()'ed path, the other option would be to create a wrapper.cmd that invokes slowproc.cmd with the pipe. Then ask cmd.exe to run wrappers.cmd.

Hope this helps.

--
Spring: Forces, Coiled Again!

In reply to Re: Win32::Process and tee by paulbort
in thread Win32::Process and tee by Sprad

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.