GNU bug report logs - #22216
test, expr Operator Precedence and Associativity

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Dan Jacobson <jidanni <at> jidanni.org>
To: bug-coreutils <at> gnu.org
Subject: test, expr Operator Precedence and Associativity
Date: Tue, 22 Dec 2015 01:18:23 +0800

$ man perlop # has a 50 line section called
   Operator Precedence and Associativity

Might (info "(coreutils) test invocation") not fully specify test's?
Might (info "(coreutils) expr invocation") not fully specify expr's?

Message #10 received at 22216-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Dan Jacobson <jidanni <at> jidanni.org>, 22216-done <at> debbugs.gnu.org
Subject: Re: bug#22216: test, expr Operator Precedence and Associativity
Date: Mon, 21 Dec 2015 18:00:42 +0000

On 21/12/15 17:18, Dan Jacobson wrote:
> $ man perlop # has a 50 line section called
>    Operator Precedence and Associativity
> 
> Might (info "(coreutils) test invocation") not fully specify test's?
> Might (info "(coreutils) expr invocation") not fully specify expr's?

expr precedence is quite well described I think.
How about this for test(1):

commit fd92e4f9c0c7465472660948008879e7e6df1de8
Author: Pádraig Brady <P <at> draigBrady.com>
Date:   Mon Dec 21 17:57:30 2015 +0000

    doc: describe test operator precedence and associativity

    * doc/coreutils.texi (Connectives for test): Add notes
    on precedence and associativity.
    Fixes http://bugs.gnu.org/22216

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 33be4d8..9fffc82 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -12645,18 +12645,23 @@ The usual logical connectives.
 @item ! @var{expr}
 @opindex !
 True if @var{expr} is false.
+@samp{!} has lower precedence than
+all components of @var{expr}.

 @item @var{expr1} -a @var{expr2}
 @opindex -a
 @cindex logical and operator
 @cindex and operator
 True if both @var{expr1} and @var{expr2} are true.
+@samp{-a} is left associative,
+and has a higher precedence than @samp{-o}.

 @item @var{expr1} -o @var{expr2}
 @opindex -o
 @cindex logical or operator
 @cindex or operator
 True if either @var{expr1} or @var{expr2} is true.
+@samp{-o} is left associative.

 @end table

Message #13 received at 22216-done <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: 22216-done <at> debbugs.gnu.org
Subject: Re: bug#22216: test, expr Operator Precedence and Associativity
Date: Tue, 22 Dec 2015 08:00:25 +0800

OK. Also make sure (info "(coreutils) test invocation") makes it clear that
one cannot use
test -f $1 -a $1 ! -ot $2 #and must use
test -f $1 -a ! $1 -ot $2 #.

Message #16 received at 22216-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>,
 Pádraig Brady <P <at> draigBrady.com>
Cc: 22216-done <at> debbugs.gnu.org
Subject: Re: bug#22216: test, expr Operator Precedence and Associativity
Date: Mon, 21 Dec 2015 17:05:09 -0700

[Message part 1 (text/plain, inline)]

On 12/21/2015 05:00 PM, 積丹尼 Dan Jacobson wrote:
> OK. Also make sure (info "(coreutils) test invocation") makes it clear that
> one cannot use
> test -f $1 -a $1 ! -ot $2 #and must use
> test -f $1 -a ! $1 -ot $2 #.

Use of -a in test is inherently non-portable.  POSIX even says so -
there are some expressions which are completely ambiguous when you
attempt to use -a or -o.

Also, your lack of quoting is a classic pitfall for how to incorrectly
use test.

Better than what you typed would be using:

test -f "$1" && test ! "$1" -ot "$2"

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

[signature.asc (application/pgp-signature, attachment)]

Message #19 received at 22216-done <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: Eric Blake <eblake <at> redhat.com>
Cc: 22216-done <at> debbugs.gnu.org,
 Pádraig Brady <P <at> draigBrady.com>
Subject: Re: bug#22216: test, expr Operator Precedence and Associativity
Date: Tue, 22 Dec 2015 08:21:16 +0800

>>>>> "EB" == Eric Blake <eblake <at> redhat.com> writes:

EB> On 12/21/2015 05:00 PM, 積丹尼 Dan Jacobson wrote:
>> OK. Also make sure (info "(coreutils) test invocation") makes it clear that
>> one cannot use
>> test -f $1 -a $1 ! -ot $2 #and must use
>> test -f $1 -a ! $1 -ot $2 #.

EB> Use of -a in test is inherently non-portable.  POSIX even says so -
EB> there are some expressions which are completely ambiguous when you
EB> attempt to use -a or -o.

Mmmm! The documentation should mention that!

EB> Also, your lack of quoting is a classic pitfall for how to incorrectly
EB> use test.

EB> Better than what you typed would be using:

EB> test -f "$1" && test ! "$1" -ot "$2"

Mmmm, quote tips only mention in the case of (info "(coreutils) String tests").
Maybe need to mention in more places!

Also no "X$1" = X special tip seen...

Message #22 received at 22216 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>,
 Eric Blake <eblake <at> redhat.com>
Cc: 22216 <at> debbugs.gnu.org
Subject: Re: bug#22216: test, expr Operator Precedence and Associativity
Date: Tue, 22 Dec 2015 01:30:24 +0000

[Message part 1 (text/plain, inline)]

On 22/12/15 00:21, 積丹尼 Dan Jacobson wrote:
>>>>>> "EB" == Eric Blake <eblake <at> redhat.com> writes:
> 
> EB> On 12/21/2015 05:00 PM, 積丹尼 Dan Jacobson wrote:
>>> OK. Also make sure (info "(coreutils) test invocation") makes it clear that
>>> one cannot use
>>> test -f $1 -a $1 ! -ot $2 #and must use
>>> test -f $1 -a ! $1 -ot $2 #.
> 
> EB> Use of -a in test is inherently non-portable.  POSIX even says so -
> EB> there are some expressions which are completely ambiguous when you
> EB> attempt to use -a or -o.
> 
> Mmmm! The documentation should mention that!
> 
> EB> Also, your lack of quoting is a classic pitfall for how to incorrectly
> EB> use test.
> 
> EB> Better than what you typed would be using:
> 
> EB> test -f "$1" && test ! "$1" -ot "$2"
> 
> Mmmm, quote tips only mention in the case of (info "(coreutils) String tests").
> Maybe need to mention in more places!

Patch V2 attached.

thanks,
Pádraig

[doc-test-logical-ops.patch (text/x-patch, attachment)]

Message #25 received at 22216 <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: 22216 <at> debbugs.gnu.org, Eric Blake <eblake <at> redhat.com>
Subject: Re: bug#22216: test, expr Operator Precedence and Associativity
Date: Tue, 22 Dec 2015 10:08:20 +0800

>>>>> "PB" == Pádraig Brady <P <at> draigBrady.com> writes:

PB> +Also @samp{!} is a shell special character and needs to be quoted.

Perhaps say instead:

Also @samp{!} is often a shell special character and is best used quoted.

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