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I am trying to match a literal string '{0,0}' using the syntax m{...}.
I know that I have to escape both the '{' and '}' characters.

Here is my program
========================
use strict;
use warnings;

$_ = '{0,0}';
if (m{\A\{0,0\}\z}) {
print "yes\n";
}
else {
print "no\n";
}
========================

The regexp works as intended and prints "yes", but there is an
unexplained warning message:

========================
Quantifier unexpected on zero-length expression in regex; marked by
<-- HERE in m/\A{0,0}\z <-- HERE / at Testregexp.pl line 5.
yes
========================

The message does not appear if I use /\A\{0,0\}\z/.

It seems to me that Perl is confused about using '{' and '}' inside a
match of the form m{...}

I am using Activestate Perl 5.10 on Windows XP.

C:\>perl -v

This is perl, v5.10.0 built for MSWin32-x86-multi-thread
(with 5 registered patches, see perl -V for more detail)

Copyright 1987-2007, Larry Wall

Binary build 1004 [287188] provided by ActiveState http://www.ActiveState.com
Built Sep 3 2008 13:16:37

--
Klaus

Klaus wrote:
>
> It seems to me that Perl is confused about using '{' and '}' inside a
> match of the form m{...}

Perl is not confused. It's a syntax error, because { and } have a special
meaning in regexes. See perldoc perlre (Section "Quantifiers").

Frank
--
Dipl.-Inform. Frank Seitz; http://www.fseitz.de/
Anwendungen für Ihr Internet und Intranet
Tel: 04103/180301; Fax: -02; Industriestr. 31, 22880 Wedel

On Apr 24, 10:32*am, Frank Seitz <devnull4...@web.de> wrote:
> Klaus wrote:
>
> > It seems to me that Perl is confused about using '{' and '}' inside a
> > match of the form m{...}
>
> Perl is not confused. It's a syntax error, because { and } have a special
> meaning in regexes. See perldoc perlre (Section "Quantifiers").

Please note that I have escaped '\{' and '\}' inside m{\A\{0,0\}\z}...

....and why does the message disappear if I use /\A\{0,0\}\z/. ?

--
Klaus

Klaus wrote:
> On Apr 24, 10:32 am, Frank Seitz <devnull4...@web.de> wrote:
>> Klaus wrote:
>>>
>>> It seems to me that Perl is confused about using '{' and '}' inside a
>>> match of the form m{...}
>> Perl is not confused. It's a syntax error, because { and } have a special
>> meaning in regexes. See perldoc perlre (Section "Quantifiers").
>
> Please note that I have escaped '\{' and '\}' inside m{\A\{0,0\}\z}...

Here, the \-escape eliminates the meaning as delimiter.
The { } become metacharacters.

> ...and why does the message disappear if I use /\A\{0,0\}\z/. ?

Here, the \-escape eliminates the meaning as metacharacter.
The { } become normal characters.

Frank
--
Dipl.-Inform. Frank Seitz; http://www.fseitz.de/
Anwendungen für Ihr Internet und Intranet
Tel: 04103/180301; Fax: -02; Industriestr. 31, 22880 Wedel

Dear Franz,

On Apr 24, 10:32*am, Frank Seitz <devnull4...@web.de> wrote:
> Klaus wrote:
>
> > It seems to me that Perl is confused about using '{' and '}' inside a
> > match of the form m{...}
>
> Perl is not confused. It's a syntax error, because { and } have a special
> meaning in regexes. See perldoc perlre (Section "Quantifiers").

No is not: the curly brackets are correctly escaped. The problem only
occurs if {} are used: other bracketing delimiters (e.g., m(\A\{0,0\}
\z) ) do not provoke the warning.

I can reproduce the problem with both 5.8.9 and 5.10.0

Matteo

Teo wrote:
> On Apr 24, 10:32 am, Frank Seitz <devnull4...@web.de> wrote:
>> Klaus wrote:
>>
>>> It seems to me that Perl is confused about using '{' and '}' inside a
>>> match of the form m{...}
>> Perl is not confused. It's a syntax error, because { and } have a special
>> meaning in regexes. See perldoc perlre (Section "Quantifiers").
>
> No is not: the curly brackets are correctly escaped. The problem only
> occurs if {} are used: other bracketing delimiters (e.g., m(\A\{0,0\}
> \z) ) do not provoke the warning.
>
> I can reproduce the problem with both 5.8.9 and 5.10.0

See <>

Frank
--
Dipl.-Inform. Frank Seitz; http://www.fseitz.de/
Anwendungen für Ihr Internet und Intranet
Tel: 04103/180301; Fax: -02; Industriestr. 31, 22880 Wedel

Klaus wrote:
> I am trying to match a literal string '{0,0}' using the syntax m{...}.
> I know that I have to escape both the '{' and '}' characters.
>
> Here is my program
> ========================
> use strict;
> use warnings;
>
> $_ = '{0,0}';
> if (m{\A\{0,0\}\z}) {
> print "yes\n";
> }
[...]
> ========================
> Quantifier unexpected on zero-length expression in regex; marked by
> <-- HERE in m/\A{0,0}\z <-- HERE / at Testregexp.pl line 5.
> yes
> ========================

Same here - Perl 5.19 on Debian/Linux.

Seems to be bug.

Workarounds:

m{\A[{]0,0[}]\z}
m{\A\{0\,0\}\z}

Helmut Wollmersdorfer

On Apr 24, 10:58*am, Frank Seitz <devnull4...@web.de> wrote:
> Klaus wrote:
> > On Apr 24, 10:32 am, Frank Seitz <devnull4...@web.de> wrote:
> >> Klaus wrote:
>
> >>> It seems to me that Perl is confused about using '{' and '}' inside a
> >>> match of the form m{...}
> >> Perl is not confused. It's a syntax error, because { and } have a special
> >> meaning in regexes. See perldoc perlre (Section "Quantifiers").
>
> > Please note that I have escaped '\{' and '\}' inside m{\A\{0,0\}\z}...
>
> Here, the \-escape eliminates the meaning as delimiter.
> The { } become metacharacters.
>
> > ...and why does the message disappear if I use /\A\{0,0\}\z/. ?
>
> Here, the \-escape eliminates the meaning as metacharacter.
> The { } become normal characters.

Ok I see but this is rather confusing:

* in a // delimited regex the literal '/' has to be escaped
* in a {} delimited regex the literal '{' has *not* to be escaped

am I getting it right?

But then when I look at perlop

When searching for single-character delimiters, escaped delimiters
and "\\" are skipped. For example, while
searching for terminating "/", combinations of "\\" and "\/" are
skipped. If the delimiters are bracketing, nested
pairs are also skipped. For example, while searching for closing
"]" paired with the opening "[", combinations of
"\\", "\]", and "\[" are all skipped, and nested "[" and "]" are
skipped as well. However, when backslashes are
used as the delimiters (like "qq\\" and "tr\\\"), nothing is
skipped. During the search for the end, backslashes
that escape delimiters are removed (exactly speaking, they are not
copied to the safe location).

it gets more confusing. If I understand correctly the difference is
only there if the { } are paired.
In m{ aaa{bbb } the { is not escaped and it is understood as the
beginning of a quantifier.

In fact I get:

Search pattern not terminated at ./test.pl line 6.

So to have a literal '{' I should escape it if not paired and not
escape it if not paired.

Did I get it wrong? (I sincerly hope so

Matteo

On Apr 24, 10:58*am, Frank Seitz <devnull4...@web.de> wrote:
> Klaus wrote:
> > On Apr 24, 10:32 am, Frank Seitz <devnull4...@web.de> wrote:
> >> Klaus wrote:
>
> >>> It seems to me that Perl is confused about using '{' and '}' inside a
> >>> match of the form m{...}
> >> Perl is not confused. It's a syntax error, because { and } have a special
> >> meaning in regexes. See perldoc perlre (Section "Quantifiers").
>
> > Please note that I have escaped '\{' and '\}' inside m{\A\{0,0\}\z}...
>
> Here, the \-escape eliminates the meaning as delimiter.

I see, thanks for the explanation.

> The { } become metacharacters.

I find it unfortunate that they become metacharacters, particularly so
because there is no reason to quote metacharacters { } in the first
place, as they always come in pairs and are handled natuarally by m{...
{ }...} as a nested pair of curlies, for example m{a{1,2}}

--
Klaus

On Apr 24, 11:12*am, Helmut Wollmersdorfer <>
wrote:
> Klaus wrote:
> > I am trying to match a literal string '{0,0}' using the syntax m{...}.
> > I know that I have to escape both the '{' and '}' characters.
>
> > Here is my program
> > ========================
> > use strict;
> > use warnings;
>
> > $_ = '{0,0}';
> > if (m{\A\{0,0\}\z}) {
> > * * print "yes\n";
> > }
> [...]
> > ========================
> > Quantifier unexpected on zero-length expression in regex; marked by
> > <-- HERE in m/\A{0,0}\z <-- HERE / at Testregexp.pl line 5.
> > yes
> > ========================
>
> Same here - Perl 5.19 on Debian/Linux.
>
> Seems to be bug.
>
> Workarounds:
>
> m{\A[{]0,0[}]\z}
> m{\A\{0\,0\}\z}

Thanks for the workarounds, they work ok. But I agree that the
original problem is a bug. Where can I post a bug report ?

--
Klaus