Re: eval segfaults when $@ isn't writable

To set $! to a constant 1, you need to give the typeglob a reference to it:

$ perl -Mwarnings -Mstrict -e'BEGIN { *! = \1; open my $fd, "< nonexis
+tent"; print "$!\n"; }'
1
[download]

It's notable that the typeglob assignment to constant destroys $!'s dual value magic:

$ perl -e'$! = 1; print "$!\n"'
Operation not permitted
[download]

I don't know whether the segfault is justified or a bug or simply undefined behavior. Just setting *@ = \1 (or 1) does not fire the segfault. I expect that die has some eval-like tendencies.

After Compline,
Zaxo

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Re^2: eval segfaults when $@ isn't writable by Hue-Bond (Priest) on Jul 04, 2006 at 10:22 UTC
To set $! to a constant 1, you need to give the typeglob a reference to it: What I meant was not to assign the constant 1 to $!, but to make $! an alias for $1, which is read only too: `! = 1; "text" =~ /.(..)/; print "$!\n"; __END__ ex` [download] It's notable that the typeglob assignment to constant destroys $!'s dual value magic:* `$ perl -e'$! = 1; print "$!\n"'` I don't get this. There's no typeglob assignment in your example. Maybe a typo? If you meant `*! = 2` then you'll get an alias for $2, as expected. So no `$!` magic. (Thank you anyway for remembering me that there's a CUFP I wanted to share :)). -- David Serrano	[reply] [d/l] [select]
Re^3: eval segfaults when $@ isn't writable by Zaxo (Archbishop) on Jul 04, 2006 at 15:31 UTC
The $! = 1; fragment was just to demonstrate the dual value magic - compare to the example before that. After Compline, Zaxo	[reply]
Re^4: eval segfaults when $@ isn't writable by Hue-Bond (Priest) on Jul 04, 2006 at 15:42 UTC
Then it isn't a typeglob assignment, and no magic is lost. This is the same code as yours, using errno 111 instead of 1: `$ perl -e'$! = 111; print "$!\n"' Connection refused` [download] Either you were fooled by the "Operation not permitted" error (which is unlikely since it isn't a Perl error according to perldiag), or I still don't get your point. -- David Serrano	[reply] [d/l]