From: Stephane Chazelas <stephane.chazelas@gmail.com>
To: Nikolai Weibull <now@disu.se>
Cc: Eric Cook <llua@gmx.com>, "zsh-users@zsh.org" <zsh-users@zsh.org>
Subject: Re: Equivalent of set -- *(DN) in sh
Date: Thu, 22 Jan 2015 15:21:40 +0000 [thread overview]
Message-ID: <20150122152139.GB8163@chaz.gmail.com> (raw)
In-Reply-To: <CADdV=MsvuSAQMJVsr17Y7g2Nfjy95CQ007opQqv-7=RHjgjaKw__35342.9068615243$1421913204$gmane$org@mail.gmail.com>
2015-01-22 08:44:40 +0100, Nikolai Weibull:
[...]
> set x *; shift
> test $# -eq 1 && test "x$1" = x\* && ! test -e \* && shift
> n=$#
> set x .[!.]* ${1+"$@"}; shift
> test $# -eq `expr $n + 1` && test "x$1" = 'x.[!.]?*' && ! test -e
> '.[!.]?*' && shift
> n=$#
> set x ..?* ${1+"$@"}; shift
> test $# -eq `expr $n + 1` && test ="x$1" = 'x..?*' && ! test -e '..?*' && shift
>
> This tries to avoid using test -e (or whatever version of testing for
> a files existence you’d like to use)
Well, it doesn't try very hard does it ;-) ? Remember you need
test -e || test -L (or test -h on some old systems).
> but also avoids using patterns
> just to test for failures to avoid unnecessary directory traversals.
The directory content will be in cache after the first `set x
*`. Forking and exeuting some exprs is probably going to be
worse in most cases.
> It also avoids messing with IFS, but perhaps that’s necessary?
Well, yes "$@" in the Bourne shell relies on it containing space
and you're leaving a number of variables and command
substitutions unquoted.
Note that "case" has far fewer problems than "test".
>
> The ${1+"$@"} is to avoid an old Zsh bug, right?
No, that's the other way round. ${1+"$@"} is to work around
problems with the Bourne shell (at least those where that has
not been fixed (where "$@" expands to one empty argument when $#
is 0)). zsh is the one that had problems with
${1+"$@"} (not "$@"), not really a bug, but down to how
parameter expansion nested.
Which is why you see things like:
test -z "$ZSH_VERSION" || alias -g '${1+"$@"}="$@"'
> It also avoids set --, as that’s apparently not portable either.
According to http://www.in-ulm.de/~mascheck/bourne/, -- was
added to the Bourne shell at the same time as [!...], so that
would suggest that if you want to account for those very old
systems, you can't use [!...] either. Note that old Bourne
shells didn't support characters with the 8th bit set either.
--
Stephane
prev parent reply other threads:[~2015-01-22 15:21 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-18 18:28 Nikolai Weibull
2015-01-18 19:07 ` Roman Neuhauser
2015-01-18 19:43 ` Nikolai Weibull
2015-01-18 20:32 ` Roman Neuhauser
2015-01-18 19:31 ` ZyX
2015-01-18 19:46 ` Nikolai Weibull
2015-01-18 20:46 ` Eric Cook
2015-01-19 15:51 ` ZyX
2015-01-19 15:55 ` ZyX
2015-01-19 16:02 ` ZyX
2015-01-19 16:16 ` ZyX
2015-01-19 21:44 ` Eric Cook
[not found] ` <54BD7ABB.5070501__36205.2317861982$1421704010$gmane$org@gmx.com>
2015-01-19 23:05 ` Stephane Chazelas
2015-01-22 7:44 ` Nikolai Weibull
[not found] ` <CADdV=MsvuSAQMJVsr17Y7g2Nfjy95CQ007opQqv-7=RHjgjaKw__35342.9068615243$1421913204$gmane$org@mail.gmail.com>
2015-01-22 15:21 ` Stephane Chazelas [this message]
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