Re: is variable with variable name possible?

[ZyX <zyx@np.by>]

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Reply to message «Re: is variable with variable name possible?», 
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
> 
> : "${(P)somevar::=$PWD}"
If we are talking about script, then you should use `emulate -L zsh' somewhere 
at the top. This will deal with all possible weird options that are set by user.

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

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