use warnings;   # it warns about undefined values
use strict;     # it's a lexically scoped declaration
use Data::Dumper;
use Fcntl qw( SEEK_SET );

$| = 1; #flushing output

my ( $mp3_size , $lines , $lines_1 , $lines_2 , $lines_3 , $lines_4 ) 
+= "\0";
my @size = "\0";

open(FH, ,"<", "song.mp3") or die "Can not open file: $!\n";
binmode(FH); # Open in binary mode.

seek( FH , 6 , SEEK_SET )
    or die "Could not seek: $!";
read( FH , $lines, 4 ); # Read 32 bits (4 Bytes) and store the data in
+ $lines Size (4 Bytes Size).
    ( $lines_1, $lines_2, $lines_3, $lines_4 ) = unpack ( "I I I I" , 
+$lines ); # (I) An unsigned integer.
    print ("This is the content of lines_1: $lines_1\n");
    print ("This is the content of lines_2: $lines_2\n");
    print ("This is the content of lines_3: $lines_3\n");
    print ("This is the content of lines_4: $lines_4\n");
    exit(0);

    $mp3_size = ($size[0] & 0xFF) |
      (( $size[1] & 0xFF ) << 7) |
    (( $size[2] & 0xFF ) << 14) |
      (( $size[3] & 0xFF ) << 21);

    print Dumper($mp3_size);

close (FH) or die "Can not close file: $!\n";

$| = 1; #flushing output
[download]

I am trying to decode the ID3v2 TAG. As my first step (code: 1) I am trying to read 4 Bytes (32 bits) of unsigned integer into the $lines[0]-$lines3 which is the header size after the 6th Byte. The first 6 Bytes I have managed to read them and decode them effectively so far but I am having trouble with this one. The reason that I am trying to decode the message in 4 different strings is that I want to apply sync_safe process after as it is displayed on the code sample above.

seek( FH , 6 , SEEK_SET )
    or die "Could not seek: $!";
read( FH , $lines, 1 );
( $lines_1 ) = unpack ( "I" , $lines );
read( FH , $lines, 1 );
( $lines_2 ) = unpack ( "I" , $lines );
read( FH , $lines, 1 );
( $lines_3 ) = unpack ( "I" , $lines );
read( FH , $lines, 1 );
( $lines_4 ) = unpack ( "I" , $lines );
[download]

Error when executing code:

This is the content of lines_0: 990183424
Use of uninitialized value $lines_1 in concatenation (.) or string at 
+test.pl line 63.
This is the content of lines_2:
Use of uninitialized value $lines_2 in concatenation (.) or string at 
+test.pl line 64.
This is the content of lines_3: 
Use of uninitialized value $lines_3 in concatenation (.) or string at 
+test.pl line 65.
[download]

I tried also to read one byte (code: 2) each time by using the read() function and unpack() one by one the 4 Bytes but I keep getting the same error message.

In theory by reading one by one the Bytes with the read() function and applying the unpack I should not have a problem, at least so far worked fine for the previous Bytes.

But by doing to in the final step I keep getting the following error:

Use of uninitialized value $lines_0 in concatenation (.) or string at 
+test.pl line 62.
This is the content of lines_0: 
Use of uninitialized value $lines_1 in concatenation (.) or string at 
+test.pl line 63.
This is the content of lines_1: 
Use of uninitialized value $lines_2 in concatenation (.) or string at 
+test.pl line 64.
This is the content of lines_2:
Use of uninitialized value $lines_3 in concatenation (.) or string at 
+test.pl line 65.
This is the content of lines_3:
[download]

I am a beginner in programming so I can not understand the reason that there is no value inside this values. Any guidance or assistance would be much appreciated

Thanks in advance for your time and effort.

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