Re: Quantifier follows nothing error in Regexp::Grammars (quantifier "?")

The question mark is a quantifier

$ perl -le " qr{\d****} "
Nested quantifiers in regex; marked by <-- HERE in m/\d** <-- HERE **/
+ at -e line 1.

$ perl -le " qr{(?#an error follows)****} "
Quantifier follows nothing in regex; marked by <-- HERE in m/(?#an err
+or follows)* <-- HERE ***/ at -e line 1.

$ perl -le " qr{?} "
Quantifier follows nothing in regex; marked by <-- HERE in m/? <-- HER
+E / at -e line 1.
[download]

You need to learn to character class :) See perlrecharclass

Try <token: punctuation> ( [.,?!"';:\-&()\[\]]+ )

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Re^2: Quantifier follows nothing error in Regexp::Grammars (quantifier "?") by hdb (Monsignor) on Oct 09, 2013 at 07:14 UTC
Minor comment: the hyphen should be the first character in the character class: `<token: punctuation> ( [-.,?!"';:\&()\[\]]+ )` [download] otherwise it is interpreted as defining a range rather than a literal hypen.	[reply] [d/l]
Re^3: Quantifier follows nothing error in Regexp::Grammars (quantifier "?") by Happy-the-monk (Canon) on Oct 09, 2013 at 07:18 UTC
the hyphen should be the first character in the character class ... otherwise it is interpreted as defining a range rather than a literal hypen. ...or the last... ...or escaped with a backslash `\`. Cheers, Sören Créateur des bugs mobiles - let loose once, run everywhere. (hooked on the Perl Programming language)	[reply] [d/l]
Re^3: Quantifier follows nothing error in Regexp::Grammars (quantifier "?") by soonix (Chancellor) on Oct 09, 2013 at 09:58 UTC
perldoc perlrecharclass says you don't need to escape `[` within a (non-Posix) character class, and for ] there is a similiar rule as for the hyphen, so `<token: punctuation> ( [][.,?!"';:&()-]+ )` [download] should be valid without any backslash. Update: corrected position of hyphen, had it outside of the regex :-/	[reply] [d/l] [select]
Re^3: Quantifier follows nothing error in Regexp::Grammars (hyphen charclass) by Anonymous Monk on Oct 09, 2013 at 08:30 UTC
Minor comment: the hyphen should be the first character in the character class: Why do you think so, what are the reasons for this habit/style? I vaguely recall maybe that I read this advice before, but it didn't stick :) (not memorable)	[reply]
Re^4: Quantifier follows nothing error in Regexp::Grammars (hyphen charclass) by hdb (Monsignor) on Oct 09, 2013 at 08:42 UTC
If you write `/[:-&]/`, you get `Invalid [] range ":-&" in regex; marked by <-- HERE in m/[:-& <-- HERE ]/` because ':' comes later in the ASCII table than '&'. If you write `/[&-:]/`, it matches each of `&'()*+,-./0123456789:`, the full range in the ASCII table between ':' and '&'. If you write `/[-&:]/`, it matches only one of `-&:` as the hyphen is not interpreted as a range operator. Of course, you can escape it with a backslash as well, which is the case in the post above but I had not seen when I first looked at it.	[reply] [d/l] [select]
Re^5: Quantifier follows nothing error in Regexp::Grammars (hyphen charclass) by Anonymous Monk on Oct 09, 2013 at 08:50 UTC
Re^4: Quantifier follows nothing error in Regexp::Grammars (hyphen charclass) by Happy-the-monk (Canon) on Oct 09, 2013 at 08:44 UTC
what are the reasons for this habit/style? in a character class, the hyphen is a range operator as in `[0-9A-Za-z]` or `[A-z]`-foolery. Cheers, Sören Créateur des bugs mobiles - let loose once, run everywhere. (hooked on the Perl Programming language)	[reply] [d/l] [select]