Shouldn't that be something like...

$ftp->cd($dir) or ($ftp->mkdir($dir) and $ftp->cd($dir));
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Technically, the most english way of writing the code (that actually works) is:

$ftp->mkdir($dir) and $ftp->cd($dir)
[download]

If you don't mind making the standard case having one extra file system access and the non-standard case having one less access.

-Ted