Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!convex!convex.COM
From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: can we ever compile perl?
Message-ID: <111032@convex.convex.com>
Date: 13 Dec 90 20:59:28 GMT
References: <9592:Dec920:40:5190@kramden.acf.nyu.edu> <110306@convex.convex.com> <1990Dec13.034336.21769@usenet@scion.CS.ORST.EDU>
Sender: news@convex.com
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
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From the keyboard of pvo@sapphire.OCE.ORST.EDU (Paul O'Neill):
:In article <110306@convex.convex.com> tchrist@convex.COM (Tom Christiansen) writes:
:>    eval "s/$find/$repl/g";
:Gee, I've always glossed over this eval stuff.  Now that I'm paying attention
:I'm befuddled.  Why is the eval needed, Tom?
:Why does the substitution 1/2 work w/o the eval?  The $find is parsed and
:found but the $repl gets shoved in literally.  I just hate it when I don't
:have a model that will predict code's behavior and have to "just try it" to
:see what it does.

Because perl only does one level of evaluation.  If you want 
more, have you to ask for it.  There are $1 and $2 references
inside of $repl.

:>Notice that I've used not one but two evals in this little program.
:Boy, I am dense.  Where's the other one?

It's hidden in the substitute that creates repl:

    ($repl = shift) =~ s/[\s_]/'$'.++$i/eg;

--tom
--
Tom Christiansen		tchrist@convex.com	convex!tchrist
"With a kernel dive, all things are possible, but it sure makes it hard
 to look at yourself in the mirror the next morning."  -me