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

Hi monks,
I have a string like this,
$str1='
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<x><chapter>
<chapnum>1A</chapnum>
</chapter>
<chapter>
<chapnum>1B</chapnum>
</chapter>
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<chapter>
<chapnum>3</chapnum>
</chapter>
<x><chapter>
<chapnum>1A</chapnum>
</chapter><x>';

[download]

I need to delete <x> tag having the condition is
First <x> tag after <chapnum>1</chapnum> with <chapnum>1A</chapnum> tags
that is 
<x><chapter><chapnum>1</chapnum></chapter><x><chapter><chapnum>1A</cha
+pnum>

[download]
</code>
to be 
<x><chapter><chapnum>1</chapnum></chapter><chapter><chapnum>1A</chapnu
+m>

[download]
</code>
i don't want to remove the last
<x><chapter><chapnum>1A</chapnum>
my output should look like this 
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<chapter>
<chapnum>1A</chapnum>
</chapter>
<chapter>
<chapnum>1B</chapnum>
</chapter>
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<chapter>
<chapnum>3</chapnum>
</chapter>
<x><chapter>
<chapnum>1A</chapnum>
</chapter><x>

[download]

I have tried like this,
$s1='<x><chapter>\s*<chapnum>1</chapnum>';
$s2='<chapter>\s*<chapnum>1A</chapnum>';

$str1 =~s#($s1)(.*?)<x>?=($s2)#$1$2$3#gsi;

[download]
Thanks in advance

Replies are listed 'Best First'.
Re: Pattern matching problem
by mantadin (Beadle) on Apr 25, 2006 at 09:32 UTC
    maybe this is what you need: 
    my $cn = qr/chapnum/;
my $cp = qr/chapter/;
$str1 =~ s#(1</$cn>\s*</$cp>\s*)<x>(<$cp>\s*<$cn>1A)#$1$2#s;

    [download]
[reply]
[d/l]
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Re: Pattern matching problem
by prasadbabu (Prior) on Apr 25, 2006 at 09:16 UTC

    Hi Anonymous Monk, Here is one way to do it. You have done couple of mistakes, you have not used the paranthesis properly for ?=$s2 and for your requirement, 'g' option modifier is not necessary. You have to take a look at perlre.

    $str1='
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<x><chapter>
<chapnum>1A</chapnum>
</chapter>
<chapter>
<chapnum>1B</chapnum>
</chapter>
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<chapter>
<chapnum>3</chapnum>
</chapter>
<x><chapter>
<chapnum>1A</chapnum>
</chapter><x>';

$s1='<x><chapter>\s*<chapnum>1</chapnum>';
$s2='<chapter>\s*<chapnum>1A</chapnum>';

$str1 =~s#($s1)((?:(?!<x>).)*)<x>(?=$s2)#$1$2$3#si;

print $str1;

output:
-------
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<chapter>
<chapnum>1A</chapnum>
</chapter>
<chapter>
<chapnum>1B</chapnum>
</chapter>
<x><chapter>
<chapnum>1</chapnum>
</chapter>
<chapter>
<chapnum>3</chapnum>
</chapter>
<x><chapter>
<chapnum>1A</chapnum>
</chapter><x>

    [download]

    update: Removed first ?:, now exactly matches your output.

    Prasad

[reply]
[d/l]
      I Saw your output that missed out first closing '</chapter>'
      Anyway thanks for your help
[reply]

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