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!
thanks,
--lx
On Fri, Aug 19, 2022 at 5:40 PM Lawrence Velázquez <
larryv@xxxxxxx> 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