From: Kurtis Rader <krader@skepticism.us>
To: ZyX <kp-pav@yandex.ru>
Cc: Zsh Users <zsh-users@zsh.org>, Ray Andrews <rayandrews@eastlink.ca>
Subject: Re: grammar triviality with '&&'
Date: Mon, 2 Mar 2015 20:43:27 -0800 [thread overview]
Message-ID: <CABx2=D8FCUQjoR7+6k9WBO3rU97tnJMFnpib5YMG1Sqcia=gew@mail.gmail.com> (raw)
In-Reply-To: <2721791425356115@web16g.yandex.ru>
[-- Attachment #1: Type: text/plain, Size: 1963 bytes --]
On Mon, Mar 2, 2015 at 8:15 PM, ZyX <kp-pav@yandex.ru> wrote:
>
> I do not think this is a mistake. And I found at least two differences:
>
> 1. `command test --help` returns zero, `command \[ --help` displays help.
> 2. `[` requires `]` (unless it received `--help` or `--version`), no
> matter what name it is called with, `test` requires not.
>
> Note that coreutils ebuild does *not* contain any references to `test` or
> `[`, patches as well do not (except when Makefile is patched not to
> regenerate man pages). This means that this difference is created by GNU
> developers, *not* by distro maintainers.
>
Ugh! I can confirm your observations using my Ubuntu 14.04 server. Yet on
Mac OS X Yosemite the two names are linked to the same binary. Mac OS X
exhibits the traditional behavior. I have no idea why GNU based distros
have the two names linked to slightly differently behaving binaries.
Presumably the GNU team had a good reason for this departure from the
traditional behavior. Furthermore, the GNU team could have used a single
binary for both names since a program can easily use the name it was
invoked by to alter its behavior. But that difference doesn't affect my
point that traditionally /bin/test and /bin/[ referred to the same program
and /bin/sh didn't know how to do anything other than invoke an external
command with a sequence of "words" and evaluate its exit status. So "if [
some condition ]; then" was really just "if /bin/[ some condition \] ;
then".
Note that quoting is critical. Which is the main reason the Korn-shell
(ksh) introduced the "[[ ... ]]" syntax. Invoking /bin/[ (or /usr/bin/[)
requires a trailing "]". Invoking /bin/test (or /usr/bin/test) requires
that there be no trailing "]". How the arguments are passed to the two
commands is also important. The "/bin/[" form requires that the shell has
already tokenized the condition into words.
--
Kurtis Rader
Caretaker of the exceptional canines Junior and Hank
next prev parent reply other threads:[~2015-03-03 4:43 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-01 16:07 Ray Andrews
2015-03-01 16:43 ` ZyX
2015-03-01 17:01 ` Ray Andrews
2015-03-01 18:48 ` Bart Schaefer
2015-03-01 19:00 ` ZyX
2015-03-01 19:16 ` Ray Andrews
2015-03-01 20:48 ` ZyX
2015-03-01 18:49 ` Lawrence Velázquez
2015-03-02 2:27 ` Vincent Lefevre
2015-03-02 3:12 ` Ray Andrews
2015-03-02 5:22 ` Lawrence Velázquez
2015-03-02 3:53 ` Kurtis Rader
2015-03-02 4:18 ` Ray Andrews
2015-03-02 5:22 ` Kurtis Rader
2015-03-02 16:17 ` Ray Andrews
2015-03-02 18:52 ` Kurtis Rader
2015-03-02 19:03 ` ZyX
2015-03-02 20:16 ` Kurtis Rader
2015-03-03 4:15 ` ZyX
2015-03-03 4:43 ` Kurtis Rader [this message]
2015-03-04 15:03 ` Vincent Lefevre
2015-03-04 19:07 ` ZyX
2015-03-02 19:25 ` Ray Andrews
2015-03-02 10:46 ` Vincent Lefevre
2015-03-02 11:06 ` Peter Stephenson
2015-03-02 19:19 ` Bart Schaefer
2015-03-04 14:47 ` Vincent Lefevre
2015-03-05 1:51 ` Bart Schaefer
2015-03-05 10:06 ` Peter Stephenson
2015-03-02 8:54 ` Bart Schaefer
2015-03-02 10:31 ` Vincent Lefevre
2015-03-02 16:31 ` Ray Andrews
2015-03-02 16:49 ` Bart Schaefer
2015-03-02 17:38 ` Ray Andrews
2015-03-02 18:51 ` Bart Schaefer
2015-03-04 8:55 ` Vincent Lefevre
2015-03-04 17:12 ` Ray Andrews
2015-03-06 4:59 ` Bart Schaefer
2015-03-06 16:10 ` Ray Andrews
2015-03-06 20:23 ` Lawrence Velázquez
2015-03-06 21:25 ` Ray Andrews
2015-03-06 16:32 ` Vincent Lefevre
2015-03-06 17:43 ` Bart Schaefer
2015-03-06 21:01 ` Ray Andrews
2015-03-09 11:26 ` Vincent Lefevre
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