Perl Substitution (REGEX) on multi line string

Question

and apologies for the newb question. I'm writing a perl script to check an MD5SUM against itself before running. Think of it as a "do not change the script check". I've managed to get the FCIV binary to calculate the MD5SUM, but there is no way to obtain just the MD5SUM as a single string output.

It spews the following to the console:

    # //
    # // File Checksum Integrity Verifier version 2.05.
    # //
    # 3e593beb3bb51a23f5a2ccae0f2c70a3 perlscript.pl

I want to procress this multi line string, capturing just the md5sum. I'm presuming the best way to do this would be with a substitution regular expression. Unfortunately though but I'm having problems with the string being over multiple lines, it emptys the whole thing.

1) Is there a better way to process this output other than a regex? 2) If we are using a regex, what would you suggest?

This is what I'm trying to us:

    $md5val =~s /(\/\/[.])*\n//;

I'm pretty new to all this, to any comments are appreciated. Thanks in advance.

choroba · Accepted Answer · 2014-08-07 11:21:26Z

1

One possible way: split on newlines, take the last line, take its second word:

#!/usr/bin/perl
use warnings;
use strict;

my $md5val = '    # //
    # // File Checksum Integrity Verifier version 2.05.
    # //
    # 3e593beb3bb51a23f5a2ccae0f2c70a3 perlscript.pl
';

$md5val = (split ' ', (split /\n/, $md5val)[-1])[1];
print "<$md5val>\n"

answered Aug 7, 2014 at 11:21

choroba

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user3691037 Over a year ago

Wow, perfect, thanks! That was a very quick reply. I've amended it slightly because the string didn't use # at the start of each line, otherwise it works as decribed.

tripleee · Accepted Answer · 2014-08-07 11:33:50Z

1

The simple and straightforward solution is to use Perl's standard library. In particular, Digest::MD5 already does what you want.

use Digest::MD5 qw(md5_hex);
my $md5val = md5_hex($data);

answered Aug 7, 2014 at 11:33

tripleee

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user3691037 Over a year ago

Thanks for the reply. I'll bear this in mind for future development. I didn't use this library because I need to be able to generate the MD5SUM and hard code it into a config file that's subsequently read by the script. This means bundling fciv. However, once the script is complete I could subsitute to this.

Miller · Accepted Answer · 2014-08-07 17:54:39Z

1

Instead of using substitution to remove everything you don't want, use a capture group to extract the part you do:

use warnings;
use strict;

my $md5val = do {local $/; <DATA>};

my ($md5sum) = $md5val =~ /\b([0-9a-f]{32})\b/;

print "$md5sum\n";

__DATA__
    # //
    # // File Checksum Integrity Verifier version 2.05.
    # //
    # 3e593beb3bb51a23f5a2ccae0f2c70a3 perlscript.pl

Outputs:

3e593beb3bb51a23f5a2ccae0f2c70a3

edited Aug 7, 2014 at 17:54

Miller

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answered Aug 7, 2014 at 11:59

RobEarl

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