I regularly have to process Comma Seperated Value or CSV files, usually for user lists. So the following perl code is a framework for processing a file line by line.

#!/usr/bin/perl
use strict;
my $line;

open(FILEIN, "filename.txt");

while(<FILEIN>)
{
  chomp();
  $line = $_;
  # Process $line for data
  # Example seperating line by commas: 
  my ($username,$firstname,$lastname,$email) = split(/,/,$line);
}

close(FILEIN);

Tags: perl, scripting

Here are some basics about Perl hashes that can be helpful to be used when an you need to associate a label with some value such as for names and telephone numbers or account numbers with amounts owed.

Create a hash variable.

my %hashvar;

Create a hash reference

my $refhash = {};

Add a value to a hash variable.

$hashvar{'somekey'} = 'someval';

Add a value to a hash reference.

$hashref->{'somekey'} = 'someotherval';

Access a value in a hash.

print $hashvar{'somekey'};

Access a value in a hash reference.

print $hashref->{'somekey}';

Access all Keys in a hash variable.
foreach my $k (keys(%hashvar))
{
print $hashvar{$k};
}

Access all Keys in a hash reference.

foreach my $k (keys(%$hashref))
{
  print $k . "n";
}

Access all Keys and values in a hash.

while (my ($key,$value) = each %hashvar)
{
  print "Key: " . $key . " has value:" . $value . "n";
}

Access all Keys and values in a hash.

while (my ($key,$value) = each %$refhash)
{
  print "Key: " . $key . " has value:" . $value . "n";
}

Assigning multiple values to a hash

%hasvar = (
  'test2' => 'myval',
  'test3' => 'myval3'
);

Note: This will clear the existing hash.

Delete a value from a hash

delete $hashvar{'key1'};

Delete a value from a hash reference.

delete $hashref->{'key1'};

Tags: hash, perl, scripting, Utilities

I use perl arrays in some of my programs, and just started to look at the regular things that I do with these arrays and thought it would be useful to keep a list of frequently used items.

Create a variable specified as an array.

my @vararray

Add an item to the beginning of an array

unshift (@vararray, "File2");

Add an item to the end of an array

push (@vararray, "File1");

Remove an item from the beginning of an array

my $var = shift(@array);

Remove an item from the end of an array

pop(@array)

Clear an array

@vararray = ();

Address an item in an array

print $vararray[0] ; 

Get the size of an array

my $arraysize = @array;

Remove an item based on the index

delete @vararray[1];

Iterate over an array

foreach my $var (@vararay)
{
  print "$var n";
}
 
# or 
my $size = @vararray;
my $i;
for ($i = 0 ; $i < @size; $i++)
{
  print "$vararray[$i]n";
}

Tags: array, perl, scripting

I was asked about system utilization on Linux systems. I found thesystatset of tools which consist of: sar, sadf, mpstat, iostat, nfsiostat, cifsiostat, pidstat and sa tools.

I will talk about the iostat tool in this article and follow up about some of the other tools.

On Ubuntu or debian systems you can install this toolset with:

sudo apt-get install sysstat

Then you will have access to the iostat command. The command output from executing with no options is below:

# iostat
Linux 2.6.32-33-generic (sumo)  09/01/2011      _i686_  (2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.11    0.00    0.47    0.01    0.00   99.41

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               0.54         1.85         8.91    1611385    7740024

This displays the avg-cpu utilization and a device usage list with basic utilization.
Some options you can use are

One more way to use the iostat tool is to specify an interval and count to the command

iostat -d -x 10 5

This will display the output 5 more times with 10 seconds between each run.

Tags: Linux, system tools, utilization

I happened to be creating a script and found myself trying to copy and past some functions between them. Well my functions
had some comments and this caused the paste operation into vi to add comments to every line after the first comment.

So this:

sub somefunc {
  # input args
  my $var1 = shift;
  my $var2 = shift;

  if ($var1 < $var2)
  {
    return $var1;
  }
  else
  {
    return $var2;
  }
}

Became this:

sub somefunc {
  # input args
  #my $var1 = shift;
  #my $var2 = shift;
  #
  #if ($var1 < $var2)
  #{
  #  return $var1;
  #}
  #else
  #{
  #  return $var2;
  #}
  #}

This made all my formatting go awry as well, and there were about 4 different functions I was about to cut and past. So I looked into how to make vi accept the text as is without adding formatting. The answer is the paste and nopaste mode.

To enter the mode to allow pasting without formatting:

:set paste

To return to regular mode:

:set nopaste

There are also ways to bind a key to more quickly enter and exit this mode if you are pasting on a regular basis.
That will be in another article.

Tags: editor, vi