Perl find size of file with Checksum ( unpack)

Posted on 2012-08-17
Medium Priority
Last Modified: 2012-08-17
I need to find and some some file sizes from a perl script there is some issues with this compare using just the files size "$x = -s $y;

I need to use Checksum to do an unpack to get what I need:

For example I can get the size I need from command line such as:

cat file.text | perl -e '$/=undef;print q{Checksum is }, (unpack(q{%32c*},<>) % 65535), qq{\n}'

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But don't seem to be putting this in the script to work correctly.

How can I do this from a script if I have a file in the script such as:

$sum = '/tmp/file1.txt';

Question by:bt707
  • 3
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Author Comment

ID: 38306447
From perldoc -f unpack:

        For example, the following computes the same number as the
        System V sum program:

            $checksum = do {
                local $/;  # slurp!
                unpack("%32W*",<>) % 65535;

I could use this but can't seem to put in what I want is to check?

The size of:
$sum = '/tmp/file1.txt';

Do I need to open and read $sum the put it in the check somehow?

LVL 28

Expert Comment

ID: 38306545
Why not use one of the many available digest modules.

Here are a few commonly used digest modules used to calculate a checksum.
Digest::CRC - Generic CRC functions
Digest::MD5 - Perl interface to the MD5 Algorithm
Digest::Adler32::XS - Generate Adler32 digests efficiently
LVL 28

Expert Comment

ID: 38306557
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Author Comment

ID: 38306585

I need a module that is already on the server, it takes forever to get a change request approved just to update a new module to the server.

I checked those, so do see one that is on the server, let me see what I need to do with that one and see if it gives what I need.

perl -MDigest::MD5  -e 'print $Digest::MD5::VERSION'

LVL 28

Accepted Solution

FishMonger earned 2000 total points
ID: 38306642
Digest::MD5 should do what you need, but you could also look at:
Digest - Modules that calculate message digests
Digest::SHA - Perl extension for SHA-1/224/256/384/512

That are both core modules so they should already be installed on your server, assuming you have a recent perl version.

Digest was first released with perl v5.7.3

Digest::SHA was first released with perl v5.9.3

Author Closing Comment

ID: 38306655
I have:

This is perl, v5.8.4 built for sun4-solaris-64int

so should have what you pointed out, just got tied up with other issues, but it looks like the info you gave should do just what I need.


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