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Stripping piece of text with RegEx

Posted on 2013-11-21
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Last Modified: 2013-11-25
I would like to be able to remove a part of text using RegEx

Example:
"[BONJOUR]Everything here should be removed as well[/BONJOUR]This part should remain"
Woud become "This part should remain".

I've tried many things, but none work:
[BONJOUR].+[/BONJOUR]
\x5bBONJOUR\x5d.+\x5b/BONJOUR\x5d

Thanks for your help.
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Question by:cdebel
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by:käµfm³d 👽
käµfm³d   👽 earned 150 total points
ID: 39666302
Try using the non-greedy version of dot-star:  .*?

Also, you need to escape the brackets since they are special characters in regex land.

e.g.

\[BONJOUR\].+?\[/BONJOUR\]

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by:pepr
ID: 39666452
As kaufmed said. Anyway, regular expressions are not powerful enough for more general cases like this because there is no way to describe nested pair structures.
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by:käµfm³d 👽
ID: 39666478
@pepr

Actually, some regex libraries support balancing groups, which can be used to match nested structures--albeit in a more complicated fashion. I think the Boost regex engine does, but I'm not 100% on that.
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by:cdebel
ID: 39666690
@kaufmed:  It's close, but it still not it.  The result i get with your expression is:
[R]This part should remain
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by:Derek Jensen
Derek Jensen earned 150 total points
ID: 39666863
@cdebel, have you tried escaping the slash?

\[BONJOUR\].+?\[\/BONJOUR\]

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by:cdebel
ID: 39666934
@bigdogdman: Yes i've tried.  The only difference between your version and Kaufmed version is the \ right before the /BONJOUR.  But i get the same result.

But there is something different if i test your expression with this website.  It seems to work there.

But does it have anything to do with boost?  I'm using this library for RegEx.  I thought RegEx was a standard... no mather which language or library i use, i was expecting the same results.

Here's my test code:
void testBoostRegex()
{
    std::string wStr = "[BONJOUR]Everything here should be removed as well[/BONJOUR]This part should remain";
    boost::regex wExp("\[BONJOUR\].+?\[\/BONJOUR\]");
    cout << boost::regex_replace(wStr, wExp, "") << endl;
    return;
}

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by:cdebel
ID: 39666955
@bigdogdman: My bad.  I've forgot to double the \.  With the following expression, it work:

    boost::regex wExp("\\[BONJOUR\\].+?\\[\\/BONJOUR\\]");

Thanks a lot!
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Accepted Solution

by:
pepr earned 200 total points
ID: 39667047
@cdebel: The problem is that you have to double backslashes in the C++ literals. It should be:
    boost::regex wExp("\\[BONJOUR\\].+?\\[/BONJOUR\\]");

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This is one of the reasons why C++11 introduced raw string literals. Now you can write:
boost::regex wExp(R"(\[BONJOUR\].+?\[/BONJOUR\])");

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Anyway, when you use C++11, the regex became the standard library.

As boost is actually a testbed for C++ standards, the C++11 regex is syntactically probably almost identical. (I have used it only the simple way, and it was identical.)

(The Microsoft Visual C++ 2013 is fairly good compiler these days, so I dare to point out to their documentation.)

For <regex> http://msdn.microsoft.com/en-us/library/vstudio/bb982382.aspx
and the regex_constants::syntax_option_type http://msdn.microsoft.com/en-us/library/vstudio/bb982516.aspx -- you can set what syntax you want to use. Anyway, the more advanced syntax also causes regular expressions be more complex in the sense of computational complexity -- see http://swtch.com/~rsc/regexp/regexp1.html

The slash need not to be escaped.
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by:käµfm³d 👽
ID: 39667943
I'm not sure that bigdogdman's post should be the accepted answer here, since it's really just a copy of what I posted. If anything, pepr's last comment should be the answer since it goes into detail about the need for double-escaping of the backslash--something I mistakenly assumed would be understood given the target language of C++.
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by:pepr
ID: 39668221
@kaufmed: I was late :) Anyway, things are as they are, and it is OK.
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by:Derek Jensen
ID: 39668971
Sorry kaufmed, I didn't mean to steal any poins from you; my bad. :">
I'll try to remember to credit you (or anyone) from now on when I'm merely offering an adjustment to their suggestion.
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by:käµfm³d 👽
ID: 39669065
It's not so much the points as the correctness. The OP stated that my suggestion didn't work (which we now know was due to lack of escaping). You're suggestion assumes that the issue is with the forward slash, which it is not. The only languages that require a forward slash to be escaped are those which use pattern delimiters (e.g. PHP, Perl, Javascipt, etc.). So in a technical sense, your answer is a repeat of my answer.

I see now that the OP posted info regarding the double-backslash as well.
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by:cdebel
ID: 39669067
I just want to point out that:
pepr reply happend after i've accepted the answer.  I would have gave him some points for the additionnal information that he have provided
bigdogdman didn't just "copy&paste" your version, but he have shown the exact version that work.  In kaufmed version, a \ was missing before the [\/BONJOUR].  I wouldn't feel correct for E-E readers if i accepted a "partially working" version just based on the fact that you answered first.
I've found the double backslash myself, you can see it with the timestamps.

I'll ask the moderator to split the point equally between the 3 of you, or reopen the question so i can accept the answer properly.

By the way, there will be a similar question in the next hour.  This question was "over simplified".  If i try to adapt to the real situation i'm facing, it still doesn't work
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by:käµfm³d 👽
ID: 39669079
Don't sweat it. I've said my peace, and you have your answer. Nobody lost a limb. It's a good day for everyone  ; )
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by:cdebel
ID: 39669129
I just want that everyone feel ok with the answer.  I didn't know that it was different for PHP/Perl/Javascript.  When i've posted this question, i've written in the tags "boost" because this is the library that i use (boost::regex_replace to be precise).  And i've posted this in regular expression, and "C++ Languages".  

But ... i was testing it in myregextester web site, because i thought i've made a mistake with my usage of boost library.

I know how it feel when someone accept the wrong answer or when the OP didn't specified things.
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by:cdebel
ID: 39669246
There's no way to ask a related question anymore, so here's the link for those who are interrested to give precisions:
http://www.experts-exchange.com/Programming/Languages/Regular_Expressions/Q_28301459.html
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by:pepr
ID: 39676136
Well, thanks for the points. Anyway, you should know I am not doing it for the points. (It is a game.) I am learning and repeating via searching for the answer. That's it. :)

Have a nice time (all of you).
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