Re: Use of == in functions

[Stephane Chazelas <stephane.chazelas@xxxxxxxxx>]

[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