How we can separate a backref from a digit?

Serge314 has asked for the wisdom of the Perl Monks concerning the following question:

Hello,

How we can separate a backreference from a digit?

print "Match1\n" if "aa1" =~ /^(a)\1(#)1$/;  # comment not works
print "Match2\n" if "aa1" =~ /^(a)\1.{0}1$/; # works, but it's very ug
+ly
print "Match3\n" if "aa1" =~ /^(a)\1 1$/x;   # works, but I don't want
+ to use x modifier...
print "Match4\n" if "aa1" =~ /^(a)\g{1}1$/;  # works, but since Perl 5
+.10...
[download]

Regards
Serge

Comment on How we can separate a backref from a digit? Download Code

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Re: How we can separate a backref from a digit? by ikegami (Patriarch) on Mar 18, 2011 at 07:17 UTC
Using `(?:\1)` works.	[reply] [d/l]
Re^2: How we can separate a backref from a digit? by Serge314 (Acolyte) on Mar 18, 2011 at 07:58 UTC
It looks good. By the way: `$a=1; print "Match\n" if "aa1" =~ /^(a)\1$a$/; # not match!` [download] After interpolation of variables we get the false backlink \11! To all: should I submit a bug report to perl.org? Serge	[reply] [d/l]
Re^3: How we can separate a backref from a digit? by ikegami (Patriarch) on Mar 18, 2011 at 07:59 UTC
Not a bug.	[reply]
Re^4: How we can separate a backref from a digit? by Serge314 (Acolyte) on Mar 18, 2011 at 08:06 UTC
Re^5: How we can separate a backref from a digit? by Jenda (Abbot) on Mar 18, 2011 at 11:13 UTC
Some notes below your chosen depth have not been shown here
Re^5: How we can separate a backref from a digit? by ikegami (Patriarch) on Mar 18, 2011 at 08:14 UTC
Re: How we can separate a backref from a digit? by BrowserUk (Patriarch) on Mar 18, 2011 at 07:30 UTC
A few more ways, I think the last would be my choice `print "Match1\n" if "aa1" =~ /^(a)\1()1$/;; Match1 print "Match1\n" if "aa1" =~ /^(a)\1(?:)1$/;; Match1 print "Match1\n" if "aa1" =~ /^(a)\1(?:1)$/;; Match1 print "Match1\n" if "aa1" =~ /^(a)\1+1$/;; Match1 print "Match1\n" if "aa1" =~ /^(a)\1{1}1$/;; Match1` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
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Re: How we can separate a backref from a digit? by JavaFan (Canon) on Mar 18, 2011 at 10:02 UTC
The problems you mention are exactly why 5.10 has \g{}. Pre-5.10, you'll have to use an ugly fix. And it can even be worse: `/....\11..../` [download] Backref to the 11th set of parenthesis, or a tab?	[reply] [d/l]
Re: How we can separate a backref from a digit? by Anonymous Monk on Mar 18, 2011 at 07:14 UTC
whitespace `/ ^ # sos (a) # $1 \1 # its $1 again $ # eos /x;` [download] See perlre, perlretut	[reply] [d/l]