Indeed I originally read that particular faq while I were regularly on clpmisc, as individual faq entries were randomly posted there. Back then I felt intrigued by the possibility, and I tried it on Linux. I can't remember which {perl,kernel} version it was, but it didn't appear to work.

Whatever, I don't know about other unices, but under Linux I guess that programs like ps just check /proc/$pid/cmdline, and I doubt (but I'm far from being sure!) that there are other ways to recover the same info.

Now, as of my experiment of yesterday, it seems that at least with recent enough perls and kernels (5.8.7 and 2.6.13 respectively, here) assigning to $0 actually writes into /proc/self/cmdline:

$ perl -le '$0="foo"; print <>' /proc/self/cmdline 
foo
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