syphilis has asked for the wisdom of the Perl Monks concerning the following question:

In recent versions of blead (including current 5.21.5) I get: 
C:\>perl -le "$_ =~ /sub mymy{ }/;"
Unescaped left brace in regex is deprecated, passed through in regex; 
+marked by <-- HERE in m/sub mymy{ <-- HERE  }/ at -e line 1.
C:\>

[download]
That's easily fixed: 
C:\>perl -le "$_ =~ /sub mymy\{ }/;"

C:\>

[download]
But why not also (or instead) deprecate the unescaping of the *right* brace ?

Cheers,
Rob

Replies are listed 'Best First'.
Re: No need to escape right brace in regex
by Athanasius (Archbishop) on Oct 21, 2014 at 04:40 UTC

    I don’t know why, but this behaviour is apparently by design:

    A literal "{" should now be escaped in a pattern

    If you want a literal left curly bracket (also called a left brace) in a regular expression pattern, you should now escape it by either preceding it with a backslash ("\{") or enclosing it within square brackets "[{]", or by using \Q; otherwise a deprecation warning will be raised. This was first announced as forthcoming in the v5.16 release; it will allow future extensions to the language to happen.

    — perl5211delta#Deprecations

    Presumably the planned “future extensions to the language” (whatever they are) won’t be affected by unescaped right braces.

    Hope that helps,

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

[reply]
[d/l]
[select]

      { is only special if it's followed by /\d+,?\d*}/. If they want to add anything else that can go between { }, they have to either add a simple rule to the language (always backslash { unless you want special behavior), or a bunch of weird rules that they might want to change again later.

      } is never special unless a preceding { makes it so.

[reply]
        But you don't *always* get the deprecation warning: 
        C:\>perl -le "$_ =~ /{}/;"

C:\>perl -le "$_ =~ /.+{}/;"

C:\>perl -le "$_ =~ /a+{}/;"

C:\>perl -le "$_ =~ /(a+)?{}/;"

C:\>perl -le "$_ =~ /a{}/;"
Unescaped left brace in regex is deprecated, passed through in regex; 
+marked by
<-- HERE in m/a{ <-- HERE }/ at -e line 1.

C:\>perl -le "$_ =~ /\d{}/;"
Unescaped left brace in regex is deprecated, passed through in regex; 
+marked by
<-- HERE in m/\d{ <-- HERE }/ at -e line 1.

C:\>

        [download]
        That behaviour fits ok with the (undetailed) documentation that Athanasius found, but does it tie in at all with the cases you're describing ?
        (I don't see the connection, though that doesn't mean there isn't one :-)

        Cheers,
        Rob
[reply]
[d/l]
        Hmm I think it's even more complicated, there is still (?{code}) and (??{code}) to handle.

        But yes looks like they are cleaning up some messi parsing rules.

        Cheers Rolf

        (addicted to the Perl Programming Language and ☆☆☆☆ :)

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[d/l]
[select]
Re: No need to escape right brace in regex
by biohisham (Priest) on Oct 21, 2014 at 09:30 UTC

    With Perl 5.18.2 on a Ubuntu 14.04 box I don't seem to get any error if I replace the double quotes for single quotes around the code, but when I try to reproduce the behavior in the cases you report (a.k.a escaping the brace or leaving it unescaped ) I get the following error 

    perl -le "$_=~/sub mymy\{}/;"

syntax error at -e line 1, near ";=~"
Execution of -e aborted due to compilation errors.

    [download]

    The error is consistently reported in all the cases you mentioned in your follow-up reply too

    A 4 year old monk
[reply]
[d/l]
[select]
      Yes, I'm on Windows. I think you really need to stick with single quotes on Ubuntu, otherwise things get a bit weird with the setting and interpolation of $_.
      The Windows shell doesn't interpolate on the "$" sign - as "$" isn't meaningful on Windows like it is on Linux.

      On my Ubuntu-14.04 with perl-5.18.0, the first time I run the command quoted above, it's fine.
      But after that I get errors too. 
      sisyphus@sisyphus5-desktop:~$ echo $_
PATH
$ perl -le "$_=~/sub mymy\{}/;" # No error here
$ echo $_
PATH=~/sub mymy\{}/;
$ perl -le "$_=~/sub mymy\{}/;"
Backslash found where operator expected at -e line 1, near "mymy\"
syntax error at -e line 1, near "mymy\"
Execution of -e aborted due to compilation errors.

      [download]
      The actual error messages can vary a bit, depending upon what gets run when - but I've seen the same error as you reported.

      Cheers,
      Rob
[reply]
[d/l]
        That's right. The Windows shell does not apply on the "$" sign and is not significant on Windows as it is usually with Linux.

        Get an email address
[reply]

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