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From: Liu Xin <navy.xliu@gmail.com>
To: "Lawrence Velázquez" <larryv@zsh.org>
Cc: zsh-workers@zsh.org
Subject: Re: An incompatible behavior from bash?
Date: Mon, 22 Aug 2022 00:54:19 -0700	[thread overview]
Message-ID: <CAHPdc0k4mzMhR2zfkmkA8ufLm6wKKMGR=vZ1iRqjG0ejmgEu+g@mail.gmail.com> (raw)
In-Reply-To: <605183ae-f347-4f64-bf99-e89f98b6637e@www.fastmail.com>

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Hi, Lawrence,

I hold the wrong impression that zsh is compatible with bash. I just assume
it because I see both Ubuntu and MacOS have replaced bash with it.
Thank you for your explanation. Indeed, it uses letter l as a word modifier
(14.1.4 Modifiers). I will read the zsh manual!


On Fri, Aug 19, 2022 at 5:40 PM Lawrence Velázquez <larryv@zsh.org> wrote:

> On Fri, Aug 19, 2022, at 6:32 PM, Liu Xin wrote:
> > I think zsh is compatible with bash
> It is only partially compatible, and compatibility is not a development
> priority.  The notion that zsh is a fancy superset of bash is false;
> zsh will only run simple bash scripts correctly.  (Whether it errs
> loudly or quietly depends on the feature used.  Using sh emulation
> may also help.)
> You are better off assuming that an arbitrary bash feature *does
> not* work with zsh unless proven otherwise, rather than assuming
> that it *does* work.
> > but I found one different behavior
> > in parameter expansion.  In the following example, I guess zsh
> > interprets "$1:l" as a whole. Is it intentional?
> Yes.  From the documentation you linked:
>         In addition to the following operations, the colon modifiers
>         described in "Modifiers" in "History Expansion" can be
>         applied: for example, ${i:s/foo/bar/} performs string
>         substitution on the expansion of parameter $i.
>         [...]
>         ${name}
>                 The value, if any, of the parameter _name_ is
>                 substituted.  [...]  In addition, more complicated
>                 forms of substitution usually require the braces
>                 to be present; exceptions, which only apply if the
>                 option KSH_ARRAYS is not set, are a single subscript
>                 or any colon modifiers appearing after the name
>                 [...].
> Your example applies the "l" history modifier, which converts the
> expansion to lowercase.  This is more obvious with a different
> choice of value:
>         % export VAR=HELLO
>         % zsh -c 'echo "$VAR:l"'
>         hello
> Braces are required if KSH_ARRAYS is set (either explicitly or via
> sh/ksh emulation).
>         % zsh --emulate sh -c 'echo "$VAR:l"'
>         HELLO:l
>         % zsh --emulate sh -c 'echo "${VAR:l}"'
>         hello
> --
> vq

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  reply	other threads:[~2022-08-22  7:59 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-19 22:32 Liu Xin
2022-08-20  0:39 ` Lawrence Velázquez
2022-08-22  7:54   ` Liu Xin [this message]
2022-08-22 21:44     ` Bart Schaefer
2022-08-23  5:42       ` Liu Xin

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