Discuss Array of hashes... what am i doing wrong? in the Perl Programming forum on Dev Shed. Array of hashes... what am i doing wrong? Perl Programming forum discussing coding in Perl, utilizing Perl modules, and other Perl-related topics. Perl, the Practical Extraction and Reporting Language, is the choice for many for parsing textual information.
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Array of hashes... what am i doing wrong?
so what i'm trying to do is this
1)read in a file with random header information
2)once it hits the line "DS,,SNMPKEYINFO," turns into CSV
3)CSV parse, allow for commas (will always be between qoutes if there are any in the value of the CSV)
4)store the values in @temparray
5)after i store the values (array size will always be 11) i then want to put it in a hash %dbstrings ($temparray[0] will always be a number, but don't know how much could be 1 to 100)
if i refer to the hash in my code in the while loop, success.
if i refer to the hash after i close <EXPORTINFO>, failure.
Code:
while(<EXPORTINFO>)
{
if($startcapture==1)
{
$string=$_;
chomp($string);
@letter=split(undef,$string);
$inqoutes=0;
$index=0;
for ($count = 0; $count<= $#letter; $count++)
{
if($letter[$count] eq ',' && $inqoutes == 0)
{
$index++;
next;
}
if($letter[$count] eq '"')
{
if ($inqoutes==0){$inqoutes=1;}
elsif ($inqoutes==1){$inqoutes=0;}
}
$temparray[$index]=$temparray[$index].$letter[$count];
#at the end of the configurations, pop the DE off and continue on
if($temparray[$index] =~ m/^DE$/i) {pop(@temparray);}
}
$var = $temparray[0];
%dbstrings = ( $var =>
{
ip=> $temparray[1],
port=> $temparray[2],
v3user=> $temparray[3],
contextid=> $temparray[4],
contextname=> $temparray[5],
seclev=> $temparray[6],
authalg=> $temparray[7],
privalg=> $temparray[8],
authkey=> $temparray[9],
privkey=> $temparray[10],
}
);
}
undef @temparray;
}
if(m/DS,,SnmpKeyInfo,/i)
{
$startcapture=1;
}
if (m/^DE/)
{
$startcapture=0;
}
}
close(EXPORTINFO);
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There's a few things wrong. First of all, when you have a parsing question you should provide sample data. It's just a waste of time to ask people to guess at what the file looks like, and to make the same assumptions you did. There could be better ways of doing things.
That's a sort of general comment borne of frustration of people rarely providing a good sample up front. Since you say it is a CSV file, I'll continue by recommending you use Text::CSV available at CPAN. If you install Text::CSV_XS as well, the parsing will be even faster.
Another thing that seems curious is that you titled your post "Array of hashes", but I don't see an array. It appears that %dbstrings is a hash of hashes. The keys, based on the first field of each row, point to a sub-hash. If that isn't the structure you want, let me know. A hash of hashes is a good structure when you know you your keys will be unique. Since your keys are just numbers, that might not be true. Any duplicates in the file will overwrite earlier entries.
Code:
by the way, my example of printing a hash value is like this:
Code:
print %dbstrings->{'1'}->{'ip'};
That's no good. When you are trying to reach a specific element, you drop the collection identifier (% for hash, @ for array) and use $ as in a single scalar. It's like the difference between singular and plural.
Single hash element is $dbstrings{1}{ip}; The quotes around keys are optional.
You only need an arrow (->) when the first variable you refer to in an expression is a reference. Perl will figure out the things beneath. In other words, you never need arrows between the elements of deeply nested structures, only after the first thing if it is a reference. Since %dbstrings is an actual hash rather than a reference, no arrow needed.
Last edited by keath : September 22nd, 2012 at 10:18 AM.
Posts: 4,085
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Here's an example of parsing with Text::CSV
Code:
#!/usr/bin/perl
use strict;
use warnings;
use Text::CSV;
use Data::Dumper;
my %data;
my @hashkeys = qw/ip port v3user contextid contextname seclev authalg privalg authkey privkey/;
my $csv = Text::CSV->new ( { binary => 1 } ) or die "Error: ".Text::CSV->error_diag ();
open my $fh, "<", "test.csv" or die "test.csv: $!";
# advance through the file until you reach your starting point
while (<$fh>) {
last if substr($_,0,16) eq 'DS,,SNMPKEYINFO,';
}
# begin processing CSV rows
while ( my $row = $csv->getline( $fh ) ) {
my %rowhash;
@rowhash{@hashkeys} = @$row[1..10];
$data{$row->[0]} = \%rowhash;
}
$csv->eof or $csv->error_diag();
close $fh;
print Dumper \%data;
Rather than assigning keys to %data, you could push each parsed row into an array @data. It depends on what you intend to do later.
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thanks for the reply,
the version of perl i'm using is a custom lightweight version that i can't modify or add packages to. those are just the rules where i am.
The issue isn't parsing. i've verified the parsing is working (by printing the value of @temparray)
the file i'm parsing is basically a database for snmpv3 devices so the file isn't entirely a CSV, there is some random header information it needs (to load into the database) here is an example of the csv portion:
note: there is potential for the username/passwords to contain commas thats why i was parsing with my method.
1,10.1.1.1,snmpv3username,"","",authPriv,SHA,AES,"authpassword","privpassword"
2, etc
3, etc will always be in increasing order i'll never know how much
when the array fills it fills correctly (verified via a printout) and i assign it to the hash it doesn't persist through out the program.
it prints out correctly in the "while loop" (via print %dbstrings->{'1'}->{'ip'};) but after i close the file it won't print out. it must be that i'm using it incorrectly. its been a while since i've used hashes in perl and refreshing the syntax is killling me. my new weekend goal is to read the cook book.
i used your suggestion of "$dbstrings{1}{ip}" for calling the value of the hash. stil works if i place it in the while loop. as soon as i exit and try to print it, it fails. just doesn't seem like it holds the value.. how would you go about iterating through the hash? here is what i'm using and it isn't printing out anything.
You want the pure Perl (XS = in C and needs to be compiled).
Anyway ... this should probably look something like:
Code:
foreach my $key (keys %dbstrings){
print $key." ";
my $key_string = $dbstrings{$key};
foreach my $entry (keys %{$key_string}){
print " " . $key_string->{$entry}. "\n";
}
}
You are mixing up plain hashes (%hash and $hash{key}) and hash-references ($hash and $hash->{key}).
And if you just want to check if you've got correct data read and in correct structure/format - just use Data:umper.
Code:
use Data::Dumper;
...
print Dumper( \%dbstrings );
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Posts: 4,085
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Quote:
the version of perl i'm using is a custom lightweight version that i can't modify or add packages to. those are just the rules where i am.
This is almost never true. Many perl modules are pure perl. In other words, they are just text files. Text::CSV is such a module. You can see part of the code right here:
Text::CSV_XS on the other hand needs to be compiled, so requiring that module could be difficult. But Text::CSV will fall back on the pure perl version when XS is not present.
You can view the manifest for any module at CPAN, and review its dependencies, and whether it contains any xs files. When they don't, you can just copy and paste the code to your own local library. You can tell perl to use any local directory you want with the 'use lib' command at the top of your script.
Consider all the abilities that are present in the CPAN libraries, and all the pre-tested code. With all you'll gain, it's worth figuring out how to move some of these files to your own library.
so your saying the way i have it written i'm just reassigning the same "key" in the hash multiple times? end goal is to get this data into some usable format where i can call it and check for repeats, add , remove, modify
But if there was already a key of the same value, that one would be overwritten and you would only get the newest row. So if you are concerned there could be duplicate keys in your file, you would need to test before assigning.
Code:
unless (exists $dbstrings{$var}) {
$dbstrings{$var} = { #hash data }; #safe to assign
}
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thanks that makes a lot of sense.
there will never be duplicate keys in the file
- it is exported from a working database, if there was duplicates i'd be receiving "snmp communication errors" from the device because only one of the $var will exist.
never hurts to throw in a check though.
this script is going to save me a lot of time versus manually added stuff to the db.
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