use strict;
use warnings;

my ($msisdn, $odbic, $odboc);
while (<DATA>) {
    if (/<SUBEND/) {
        print "$msisdn,$odbic,$odboc\n";
        $msisdn = "Update Command MSISDN=notSet";
    }
    
    $msisdn = "Update Command <$1>" if /^\s*MSISDN=(\d+);/;
    $odbic = $1 if /^\s+ODBIC=(\w+);/;
    $odboc = $1 if /^\s+ODBOC=(\w+);/;
}

__DATA__

<SUBBEGIN
    MSISDN=123476789678;
    ODBIC=BIC;
    ODBOC=BAOC;
<SUBEND
<SUBBEGIN
    ODBIC=BIC;
    ODBOC=BAOC;
<SUBEND

##</code><code>##

Update Command <123476789678>,BIC,BAOC
Update Command MSISDN=notSet,BIC,BAOC