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From: Stephane Chazelas <stephane.chazelas@gmail.com>
To: zsh-users@zsh.org
Subject: Re: Use of == in functions
Date: Sun, 12 Jan 2020 12:03:53 +0000
Message-ID: <20200112120353.snhivqosevvv526a@chaz.gmail.com> (raw)
In-Reply-To: <20200112100906.GA95942__47727.4053309642$1578823915$gmane$org@pooh.prefix.duckdns.org>

[repost to zsh-users. I'll see if I can add a mutt hook to avoid
the problem in the future].

2020-01-12 11:09:06 +0100, Kusalananda Kähäri:
[...]
> == within [[ ]]
> =  within [   ]
> 
> ... just like in bash (but bash allows its built in test/[ utility to
> understand == too)
[...]

zsh's [ builtin also supports == as an alias of = (like its [[
]] construct also supports == as an alias of =), but in zsh,
=cmd is an operator that expands to the path of the cmd command,

$ echo =ls
/usr/bin/ls

so you would need:

[ a '==' b ]

(or disable the =cmd feature with set +o equals) if for some
reason you wanted to use the non-standard == in place of =.

Just like you need

[ a '=~' regex ]

for regex matching.

And

[ a '<' b ]

to compare strings lexically as < is also a redirection
operator.

Now, as none of <, ==, =~ are standard [ operators (so sh
compatibility is no longer a good reason to use the "["
command), you might as well use the ksh-style [[...]] construct
which doesn't have this kind of issue:

[[ a =~ b ]], [[ a < b ]], [[ a == b ]] are all fine (but then
again, there's no need to double the =. == is an operator that
is needed in languages where there's a need to disambiguate
between assignment and equality comparison, but inside [[...]]
(as opposed to ((...)) for instance), there's no assignment)


-- 
Stephane



  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-12  8:34 Frank Gallacher
2020-01-12 10:09 ` Kusalananda Kähäri
2020-01-12 10:33   ` SUMMARY " Frank Gallacher
     [not found] ` <20200112100906.GA95942__47727.4053309642$1578823915$gmane$org@pooh.prefix.duckdns.org>
2020-01-12 12:03   ` Stephane Chazelas [this message]
2020-01-12 13:58     ` Daniel Shahaf

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