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From: ZyX <zyx.vim@gmail.com>
Reply-To: zyx.vim@gmail.com
To: Mikael Magnusson <mikachu@gmail.com>,
 Zsh Users <zsh-users@zsh.org>
Subject: Re: is variable with variable name possible?
Date: Tue, 5 Apr 2011 08:04:59 +0400
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Reply to message =ABRe: is variable with variable name possible?=BB,=20
sent 00:50:02 05 April 2011, Tuesday
by Stephane Chazelas:

> In your example, if we have to accomodate users enabling
> shwordsplit or globsubst (or running zsh in sh or ksh
> emulation), we need
>=20
> : "${(P)somevar::=3D$PWD}"
If we are talking about script, then you should use `emulate -L zsh' somewh=
ere=20
at the top. This will deal with all possible weird options that are set by =
user.

> eval "$somevar=3D\$(pwd)"
> or
> eval "$somevar=3D\$PWD"
>=20
> are POSIX and POSIX shells have globsubst and shwordsplit on.
> The above will work regardless of the status of those options.
Somebody said that $somevar contains nothing harmful?

Original message:
> 2011-04-04 18:34:26 +0200, Mikael Magnusson:
> [...]
>=20
> > >> > eval "$somevar=3D\$(pwd)"
> > >> > or
> > >> > eval "$somevar=3D\$PWD"
>=20
> [...]
>=20
> > >> How do you feel about this?
> > >>=20
> > >> : ${(P)somevar::=3D$PWD}
> > >=20
> > > [...]
> > >=20
> > > Try after
> > >=20
> > > sudo ln -s . '/*'
> > > cd '/*/*/*/*/*'
> > > setopt globsubst
> > >=20
> > > ;-)
> > >=20
> > > (if you're lucky, it won't crash your machine).
> >=20
> > Pretty sure globsubst breaks your idea too, but fine,
> >=20
> > : ${(P)~~somevar::=3D$PWD}
> >=20
> > In fact, globsubst pretty much breaks every hook function i have :P.
>=20
> [...]
>=20
> eval "$somevar=3D\$(pwd)"
> or
> eval "$somevar=3D\$PWD"
>=20
> are POSIX and POSIX shells have globsubst and shwordsplit on.
> The above will work regardless of the status of those options.
>=20
> In POSIX shells, you need to quote variables to prevent
> globsubst or shwordsplit, even in arguments to ":" because
> globsubst can be very very resource intensive.
>=20
> You can bring a machine to its knees with
>=20
> : ${var=3Dfoo}
>=20
> if $var is for instance /*/*/*/../../../*/*/*/../../../*/*/*
>=20
> So, you should either use instead:
>=20
> var=3D${var-foo}
> or
>=20
> : "${var=3Dfoo}"
>=20
> In your example, if we have to accomodate users enabling
> shwordsplit or globsubst (or running zsh in sh or ksh
> emulation), we need
>=20
> : "${(P)somevar::=3D$PWD}"
>=20
> But
>=20
> eval "$somevar=3D\$PWD"
>=20
> is more legible and more portable.

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