From: Kurtis Rader <krader@skepticism.us>
To: sergio <mailbox@sergio.spb.ru>
Cc: zsh-users@zsh.org
Subject: Re: [[ and [
Date: Sat, 3 Mar 2012 20:50:05 -0800 [thread overview]
Message-ID: <CABx2=D8ifbJB3PTJuyLPzbbiGXdMCFUrgxJGm1W27+BDEk2CjA@mail.gmail.com> (raw)
In-Reply-To: <4F52D510.6000002@sergio.spb.ru>
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To expand on Bart's reply the "if [ ]" form goes back to the original
Bourne shell (probably before you were born but not before I was born :-)
which only supported invoking external programs and evaluating their exit
status. The left square-bracket was actually a filesystem alias for
/bin/test (or /usr/bin/test). Although today it is more likely that both
the "[" and "test" commands are built-ins to the shell that exhibit the
historic semantics. Whereas "[[" is a token that triggers the shell to
parse the contents up to the matching "]]" using different rules. I believe
the "[[ ]]" notation was introduced by the Korn shell after David Korn who
wrote the first version.
On Sat, Mar 3, 2012 at 6:36 PM, sergio <mailbox@sergio.spb.ru> wrote:
> Hello.
>
> It's dumb question, but I can't find this in man.
>
> What it the difference between [[ ]] and [ ]?
> if [[ ]]; then ... fi
> and
> if [ ]; than ... fi
>
> OK, the first is an evaluating of the conditional expression, and what
> is the second?
>
> --
> sergio.
>
--
Kurtis Rader
Caretake of the exceptional canines Einstein and Chino
prev parent reply other threads:[~2012-03-04 4:50 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-04 2:36 sergio
2012-03-04 4:24 ` Bart Schaefer
2012-03-06 0:32 ` sergio
2012-03-06 6:05 ` Bart Schaefer
2012-03-06 11:05 ` sergio
2012-03-06 11:35 ` Peter Stephenson
2012-03-06 11:44 ` Peter Stephenson
2012-03-06 11:53 ` Mikael Magnusson
2012-03-07 9:02 ` Nadav Har'El
2012-03-07 9:05 ` Mikael Magnusson
2012-03-07 9:21 ` Nadav Har'El
2012-03-07 15:27 ` Bart Schaefer
2012-03-07 8:52 ` Nadav Har'El
2012-03-07 9:43 ` Peter Stephenson
2012-03-07 14:11 ` Nadav Har'El
2012-03-07 14:27 ` Peter Stephenson
2012-03-07 18:38 ` Mark
2012-03-06 16:16 ` sergio
2012-03-06 16:29 ` Peter Stephenson
2012-03-06 17:40 ` sergio
2012-03-07 8:12 ` Nadav Har'El
2012-03-04 4:50 ` Kurtis Rader [this message]
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