From: Bart Schaefer <schaefer@tiny.zanshin.com>
To: Danny Dulai <nirva@ishiboo.com>
Cc: Bart Schaefer <schaefer@zanshin.com>, zsh-users@sunsite.auc.dk
Subject: Re: Setting paths with ~'s in values.
Date: Tue, 23 Feb 1999 21:07:56 -0800 (PST) [thread overview]
Message-ID: <14035.35116.392298.579759@c-bart.amazon.com> (raw)
In-Reply-To: <19990223033938.20667@bleep.ishiboo.com>
Danny Dulai writes:
> what is the difference between [[ ... ]] and [ ... ] ?
`[[ ... ]]` is a lexical construct; in effect, `[[` and `]]` are
reserved words (though I don't recall if they're actually implemented
that way). `[` is just a command that happens to look for an argument
']', and interprets everything in between.
That means that the `...` in a `[[ ... ]]` expression can be treated
specially by the parser, so you can use things like `&&` and `||`
where `[` and `test` require -a and -o. In particular, the equality
test in a `[[`-expression uses pattern matching, so glob characters
in such expressions are not expanded against the filesystem. That's
what I've repeatedly been forgetting the last few weeks.
> Is [[ the builtin version of the test command?
No, `[` is the builtin version of `test`; but many of the conditional
expressions supported by `test` are also supported by `[[ ... ]]`,
which is the source of much of this confusion.
prev parent reply other threads:[~1999-02-24 5:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-02-12 20:17 Larry P . Schrof
1999-02-12 22:05 ` Bart Schaefer
1999-02-12 22:29 ` Bart Schaefer
1999-02-22 22:20 ` Danny Dulai
1999-02-23 4:58 ` Bart Schaefer
1999-02-23 8:39 ` Danny Dulai
1999-02-24 5:07 ` Bart Schaefer [this message]
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