in reply to Reading Binary files in Perl

For us to be able to help you, you'll have to tell us more.

I also have the structure available which tells me what the first 8 bytes are, then the next 4 bytes and so on.

A good start would be to show us what that "structure" looks like. What form is it in? How do you get it into your perl program?

I tried doing it through unpack function available in perl but i am stuck on how to get the first 8 bytes then the next 8 bytes and so on..

If you show us what you tried (post your non-working code here (don't forget the <code></code> tags), then it serves as a starting point from which we can guide you.

Replies are listed 'Best First'.
Re^2: Reading Binary files in Perl
by pranjali_malode (Initiate) on Aug 25, 2010 at 12:58 UTC
    Below is the structure or format of data in binary file: <structure> Offset Field Name size 0x0 magic_numbe 8 0x8 retry_count 1 0x9 number_record 1 0x10 dc_timestamp 8 <\structure> and the code is: 
    open(FH, "<DCdata.bin") or die "Can't open DCdata.bin file for reading
+!";
binmode(FH); 

while (<FH>)
{
    $index = 0;
    
    foreach $field_name (keys (%disk_structure)) {
        
        $value = read (FH, $buffer, ($field_name * 8), 0);
        print tell (FH);
        print "\n";
    }
    
    foreach $f_name (keys (%disk_structure_record)) {
        
        $value_record = read (FH, $buffer, ($f_name * 8), 0);
        #print tell (FH)\n;
    }
}

close(FILE);

    [download]
[reply]
[d/l]

      If your file consists of 18 character records, then the easiest way to read it is to set the input record separator ($/) to a reference to the number of bytes per record: $/ = \18;. This causes readline() (<FH>) to read the file as a series of fixed length records. You can then unpack the fields within each record very easily: 

      #! perl -slw
use strict;
 
=comment
Offset Field Name    size 
0x0    magic_numbe   8 
0x8    retry_count   1 
0x9    number_record 1 
0x10   dc_timestamp  8
=cut

open( FH, '<', DCdata.bin" ) 
    or die "Can't open DCdata.bin file for reading!";
binmode(FH); 

$/ = \18; ## set record size

while( <FH> ) {
    my( $magic, $retry, $recnum, $timestamp ) = unpack 'A8 C C A8', $_
+;
    ## Do something with the information??
}
close FH;

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
[select]

      A hash is not ordered, so it makes no sense to read the (ordered) elements from a file in a foreach loop over the hash keys.

[reply]
[d/l]

In Section Seekers of Perl Wisdom