Solved

Read binary file with known structure

Posted on 2009-04-03
2
1,635 Views
Last Modified: 2012-08-14
Hello,
I have to get a string from binary file. But to get it have to parse the file. Fortunately it's structure is known, but some parts size defined by integer numbers in the file. So it goes like this:
integer (4 bytes, little-endian)
integer
unsigned short (2 bytes)
unsigned short
integer
char [length defined by the integer above]
integer
char [length defined by the integer above]
...
...
I need to get the last string of chars above (it's not the last in the file).
My problem is I cannot get integers out of binary stream to determine the size of string after it.
Would you help please? Please use only standard Perl, no libraries.
0
Comment
Question by:yuk99
2 Comments
 
LVL 39

Accepted Solution

by:
Adam314 earned 500 total points
ID: 24064514
You can use the pack and unpack function to interact with the data.  With these functions, you give them a format code, and they convert from/to data data.

The exact format codes will depend on your data.  For details, see here:
    http://perldoc.perl.org/functions/pack.html
A summary:
  v    An unsigned short (16-bit) in "VAX" (little-endian) order.
  V    An unsigned long (32-bit) in "VAX" (little-endian) order.

##### To get just the first integer
read($FH, $string, 4);   #Read 4 bytes into $string (assumes $FH is your file handle)
my $number = unpack("V", $string);
 
#To get:
#  integer (4 bytes, little-endian)
#  integer  [I'm assuming same type: 4 bytes little-endian]
#  unsigned short (2 bytes)
#  unsigned short
#  integer  [I'm assuming same type: 4 bytes little-endian]
read($FH, $string, 16);  #Read 16 bytes
my ($int1, $int2, $short1, $short2, $int3) = unpack("VVvvV", $string);

Open in new window

0
 
LVL 15

Author Closing Comment

by:yuk99
ID: 31566431
Adam, thank you so much! Works great!
I heard I should use unpack, but could not understand how to use it. You made my day. Thanks!
0

Featured Post

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Many time we need to work with multiple files all together. If its windows system then we can use some GUI based editor to accomplish our task. But what if you are on putty or have only CLI(Command Line Interface) as an option to  edit your files. I…
Checking the Alert Log in AWS RDS Oracle can be a pain through their user interface.  I made a script to download the Alert Log, look for errors, and email me the trace files.  In this article I'll describe what I did and share my script.
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…

809 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question