You didn't convert the file names into shell string literals when you created the shell command. There are two simpler alternatives:

You can use the multi-arg form of system which passes the arguments to the child without serializing them*:

system('cp', $oldname, "renamed/$newname")
   or die("cp: $!/$?\n");
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You can use File::Copy:

copy($oldname, "renamed/$newname")
   or die("copy: $!\n");
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* — Serialization will occur in Windows, but Perl will handle quoting and escaping for you (within the limits of Windows's command line abilities).

Brilliant. Thank you so much.

Or, use the multi-argument form of system that will not call the shell. Put one argument per argument.

—John

Double quotes on a bourne shell are subject to shell interpolation. Strange filenames will bite you:

#!/usr/bin/perl -w
use strict;
die "DON'T RUN THIS SCRIPT"; # just in case ...
my ($from,$to)=('mostly-harmless.txt','$(rm -rf /)');
system(qq[cp "$from" "$to"]);
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The shell invoked (typically /bin/sh) will see the following command line:

cp "mostly-harmless.txt" "$(rm -rf /)"

Before executing cp, the shell must first evaluate "rm -rf /", as its stdout should be passed as second argument to cp.

The best way to use system is not to mess with the shell at all, i.e. to use the system LIST variant or a perl build-in. In this case, CPAN has File::Copy which handles file copying inside perl, automatically using the most efficient implementation available (system API if present, fall back to open-read-write-close), and without any quoting problems or slow sub-process invokations.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

Abigail-II has a video (presentation from a conference) where he promotes using cp not File::Copy. Personally, I think a better solution is to fix the nuances in File::Copy that he identified.