It seems to work fine for me. As soon as i copied your script, I turned off printing except for the last one and seems to have your desired output, maybe i am missing something? 
my $data_fix = "00";

while (<DATA>)
    {
    my($data1,$data2,$data3,$data4,$data5) = split(/:/);
    chomp($data5);
    $data5 .=  $data_fix;
    $data_line = $data1 . ":" . $data2 . "00" . ":" . $data3 . ":" . $
+data4 . ":" . $data5 . "\n";
    print $data_line;
    }

__DATA__
o:200806050852:b7199767:b24211012077030:200902232359
o:201103251457:b6235734:b2421100997663:201204022359
o:201403101021:b8015840:b24211013181843:201404072359
o:201407291225:b8759124:b24211001018862:201408262359

[download]
Definately outputs: 
C:\Users\James\Desktop\perlmonks>test.pl
o:20080605085200:b7199767:b24211012077030:20090223235900
o:20110325145700:b6235734:b2421100997663:20120402235900
o:20140310102100:b8015840:b24211013181843:20140407235900
o:20140729122500:b8759124:b24211001018862:20140826235900

C:\Users\James\Desktop\perlmonks>

[download]
Maybe it is time to take a step back, go get yourself something to drink or some fresh air ;)

In reply to Re: String concatenation issues with 00? by james28909
in thread String concatenation issues with 00? by bobdabuilda

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