& is not the concatenation operator in Perl. What you're looking for is the dot. For this example, there's no need to use it, though. Also, there's no reason to use backticks to get environment variables; they're stored in the %ENV hash.

my $testval = "~$ENV{USER}/foo";
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1. I'm pretty sure you mean to be using a concatentation operator, which in Perl is .. The & you are using is a bitwise AND operator.
2. Using `` causes variable interpolation, so your script is trying to interpolate a variable called $USER. Using the {} has no bearing on variable interpolation the way you are using it. You have to escape the $ with a \
3. The return value you will get from the `` will have a newline attached to it. You'll need to chomp that.

After all that you should come with something like this:

chomp($user = `echo \$USER`);
$TESTVAL = "~" . $user . "/foo";
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Of course, the methods the other monks posted are probably a better idea than this. I'm trying to show you how to properly use the operators you chose.

Hope that helps.

Amel - f.k.a. - kel

Sorry...
I am trying to write ASP, Java, Perl, and SH all at the same time for 5 different projects.
My brain is a little fried since I haven't used Perl for a while.

Update Okay, Amel, told you while I was typing this :)

                - Ant