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

Hi, In a text file, if there are any listed structures, the start and end will be marked by <bl>..</bl>. All the lines between these elements should be tagged as <listitem>..</listitem>. I wrote a code as below: 

    if (m|<bl>| .. m|</bl>|)
    {
        s/^(?!<bl>)|(?<=<bl>)/<listitem>/g;
        s-(?=</bl>)|(?<!</bl>)(?=\n)-<\/listitem>-g;
    }

[download]

This is working fine if the structure is plain like below: 

<bl>List item 1
List item 2
List item 3</bl>

[download]

But, I also encounter instances where <bl> appears within a <bl> like below: 

<bl>List item 1
List item 2
<bl>List item a
List item b
List item c</bl>
List item 3</bl>

[download]
If I run the above text with my code, the conversion fails. I intend to get the output as follows 
<listitem>List item 1</listitem>
<listitem>List item 2</listitem>
<listitem>List item a</listitem>
<listitem>List item b</listitem>
<listitem>List item c</listitem></listitem>
<listitem>List item 3</listitem>

[download]

All the entires of the sublist should be tagged and later the end tag of item 2 should be inserted. Also after finishing the sublist, tagging for the main list should continue until </bl> for the main list is encountered. I could not derive a structure to the script for this. Could someone help me on this?

Replies are listed 'Best First'.
Re: Help in using Regular Expressions
by cdarke (Prior) on Jun 12, 2008 at 07:37 UTC
    I came up with the following:
    use warnings;
use strict;

while (<DATA>) {

   s|^(?:<bl>)?(.*?)(?:</bl>)?$|<listitem>$1</listitem>|;
   print
}
__DATA__
<bl>List item 1
List item 2
<bl>List item a
List item b
List item c</bl>
List item 3</bl>

    [download]
    It does not produce exactly the intended output, but:
    <listitem>List item 1</listitem>
<listitem>List item 2</listitem>
<listitem>List item a</listitem>
<listitem>List item b</listitem>
<listitem>List item c</listitem>
<listitem>List item 3</listitem>

    [download]
    Which, to me at least, looks more likely to be useful.
[reply]
[d/l]
[select]
Re: Help in using Regular Expressions
by Anonymous Monk on Jun 12, 2008 at 07:29 UTC
    Here's an idea 
    $_ = q~<bl>List item 1
List item 2
<bl>List item a
List item b
List item c</bl>
List item 3</bl>
~;

s~</?bl>~~g;
s~(List.+?)$~<listitem>$1</listitem>~gm;

print $_,$/;

__END__
<listitem>List item 1</listitem>
<listitem>List item 2</listitem>
<listitem>List item a</listitem>
<listitem>List item b</listitem>
<listitem>List item c</listitem>
<listitem>List item 3</listitem>

    [download]
[reply]
[d/l]
Re: Help in using Regular Expressions
by Anonymous Monk on Jun 12, 2008 at 07:35 UTC
    Since look ahead/behind are zero width, your substitution will never eliminate any <bl> tags, it will just insert listitem tags
[reply]
[d/l]
Re: Help in using Regular Expressions
by pc88mxer (Vicar) on Jun 12, 2008 at 14:20 UTC
    All the entires of the sublist should be tagged and later the end tag of item 2 should be inserted. Also after finishing the sublist, tagging for the main list should continue ...
    I have a feeling that the OP wants this: 
    <listitem>List item 1</listitem>
<listitem>List item 2
  <listitem>List item a</listitem>
  <listitem>List item b</listitem>
  <listitem>List item c</listitem>
</listitem>
<listitem>List item 3</listitem>

    [download]
    (indentation added for emphasis.) Is this correct?
[reply]
[d/l]

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