How to print out matached string with perlre? - regex

Question

Perlre (Perl Regular Expression) is used for searching / replacing complex XML structure, e.g.
perl -0777 -pe 's/<ac:structured-macro ac:macro-id="[a-z0-9\-]+" ac:name="gadget" ac:schema-version="1"><ac:parameter ac:name="preferences">.*?selectedIssueKey=([A-Z\-0-9]+).*?(<\/ac:parameter>)<ac:parameter ac:name="url">https:\/\/rcrs.rbinternational.corp\/issue\/rest\/gadgets\/1.0\/g\/com.pyxis.greenhopper.jira:greenhopper-card-view-gadget\/gadgets\/greenhopper-card-view.xml<\/ac:parameter>.*?(<\/ac:structured-macro>)/<ac:structured-macro ac:name="jira" ac:schema-version="1"><ac:parameter ac:name="server">RCRS Issue Tracking<\/ac:parameter><ac:parameter ac:name="columns">key,type,assignee,status,nwu model developer,nwu model reviewer,nwu model owner,nwu head rr\/b2\/cro,ho validation owner,ho pi\/micro country manager,ho responsible signee<\/ac:parameter><ac:parameter ac:name="maximumIssues">20<\/ac:parameter><ac:parameter ac:name="jqlQuery">key = \1 <\/ac:parameter><ac:parameter ac:name="serverId">d64129aa-b1e8-3584-8953-2bd89c3e515c<\/ac:parameter><\/ac:structured-macro>/igs' macro
Currently the search pattern does not match as expected. Obviously the search patterns spans more string than expected. Is there a possibility to print out each matched string for debugging purpose?

Answer 1

You can turn on debugging for regex with use re 'debug';. However that would be the wrong approach to take. Your problem here isn't your regex is wrong, it's that regex is fundamentally the wrong tool for XML parsing. (And leaving aside that - your line is just too long to be sensible to use inline like that!)
Given your example - it looks like you're trying to extract a single value (selectedIssueKey) and insert it into a new blob of XML.
This is done much easier by a parser, such as XML::Twig. I can't give you a precise example, because I would need to see your XML structure (or at least a subset without the wildcards).
But something like this can be used for extracting a value from some XML:
#!/usr/bin/perl
use strict;
use warnings;
use XML::Twig;
my $twig = XML::Twig -> parse ( \*DATA );
my $selectedIssueKey = $twig -> findnodes ( '//ac:parameter/pref', 0) -> att('selectedIssueKey');
print $selectedIssueKey;
Extracts the value of an attribute 'selectedIssueKey' from:
<ac:structured-macro ac:macro-id="test" ac:name="gadget" ac:schema-version="1">
<ac:parameter ac:name="preferences">
<pref selectedIssueKey="anothertest" />
</ac:parameter>
<ac:parameter ac:name="url">https://rcrs.rbinternational.corp/issue/rest/gadgets/1.0/g/com.pyxis.greenhopper.jira:greenhopper-card-view-gadget/gadgets/greenhopper-card-view.xml</ac:parameter>
</ac:structured-macro>
XML::Twig also lets you cut and paste, so you could do something like this:
#!/usr/bin/perl
use strict;
use warnings;
use XML::Twig;
my $twig = XML::Twig -> new ( 'pretty_print' => 'indented_a' ) -> parsefile 'sample.xml' );
my $selectedIssueKey = $twig -> findnodes ( '//ac:parameter/pref', 0) -> att('selectedIssueKey');
print "Found key of: $selectedIssueKey\n";
my $ac_structured_macro = $twig -> findnodes ( '//ac:structured-macro',0 );
my $new_macro = $twig -> root -> insert_new_elt( 'last_child', 'ac:structured-macro', { "ac:name" => "jira", "ac:schema-version"=> "1" } );
$new_macro -> insert_new_elt('last_child', 'ac:parameter', { 'ac:name' => 'server' }, "RCRS ISSUE Tracking" );
$new_macro -> insert_new_elt('last_child', 'ac:parameter', { 'ac:name' => 'columns' }, "key,type,assignee,status,etc" );
$new_macro -> insert_new_elt('last_child', 'ac:parameter', { 'ac:name' => 'maximumIssues' }, "20" );
$new_macro -> insert_new_elt('last_child', 'ac:parameter', { 'ac:name' => 'jqlQuery' }, "key = $selectedIssueKey" );
$new_macro -> insert_new_elt('last_child', 'ac:parameter', { 'ac:name' => 'serverId' }, "d64129aa-b1e8-3584-8953-2bd89c3e515c" );
$ac_structured_macro -> delete;
$twig -> print;
(It's probably easier to use a whole XML snippet for this though, and just replace the bits yo uwant).

Answer 2

use re 'debug'
To debug you regex, read more about it here http://perldoc.perl.org/re.html#%27debug%27-mode

Answer 3

Use a CPAN module for this. May save you some headache.
But if you still want to use regex for the job, I'd suggest you expand the regex in a script and step through it using the debugger like mentioned above.