(Update: Noticed that UserIDs could repeat; changed code to merge values for duplicate UserIDs.)

Here's one way of doing it that stores the data as a hash of hashes:

    #!/usr/bin/perl

    use warnings;
    use strict;

    my %user_data;
    my $current_user;

    while (<DATA>) {
        if (my ($elem, $content) = m|^ <([^>]+)> (.*) </\1> |x) {
            $current_user = $content if $elem eq "UserID";
            $user_data{$current_user}{$elem} = $content;
        }
        else {
            print "Bad line $.: $_";
        }
    }

    use Data::Dumper;
    print Dumper(\%user_data);

    # $VAR1 = {
    #   '98766' => {
    #                'var6' => 'some string',
    #                'var1' => 'some string',
    #                'dev' => 'Some Text',
    #                'UserID' => '98766',
    #                'var2' => 'some string',
    #                'var5' => 'some string',
    #                'start' => '2004-10-21TO09:57:25Z'
    #              },
    #   '57864' => {
    #                'var6' => 'some string',
    #                'var1' => 'some string',
    #                'dev' => 'Some Text',
    #                'var4' => 'some string',
    #                'UserID' => '57864',
    #                'start' => '2004-10-25TO09:57:25Z'
    #              },
    #   '46786' => {
    #                'var3' => 'some string',
    #                'var1' => 'some string',
    #                'dev' => 'Some Text',
    #                'var4' => 'some string',
    #                'UserID' => '46786',
    #                'var2' => 'some string',
    #                'start' => '2004-10-21TO09:57:25Z'
    #              }
    # };


    __DATA__
    <UserID>46786</UserID>
    <start>2004-10-21TO09:57:25Z</start>
    <dev>Some Text</dev>
    <var1>some string</var1>
    <var2>some string</var2>
    <UserID>57864</UserID>
    <start>2004-10-25TO09:57:25Z</start>
    <dev>Some Text</dev>
    <var1>some string</var1>
    <UserID>46786</UserID>
    <var3>some string</var3>
    <var4>some string</var4>
    <UserID>98766</UserID>
    <start>2004-10-21TO09:57:25Z</start>
    <dev>Some Text</dev>
    <var1>some string</var1>
    <var2>some string</var2>
    <var5>some string</var5>
    <var6>some string</var6>
    <UserID>57864</UserID>
    <var4>some string</var4>
    <var6>some string</var6>
[download]

When parsing files, it's a good idea to detect and report errors. A few of your sample lines, for example, had opening and closing tags that didn't match. I fixed them in my example data, but only after the error-reporting code caught them.

Cheers,
Tom

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