Perl Config File

We can make use of Config::Simple module for this.
This library supports parsing, updating and creating configuration files.

Main Features of Config::Simple are as mentioned below:
1) It allows to read config file in different formats/styles like INI-FILE format and HTML format.
2) It allows to read config file in the form of objects and access the variables from the object.
3) It allows to fetch all the variables at into a hash/hashref using "vars" method.

Let's discuss how can we read/modify/write config files easily in perl as mentioned below :
Reading config file in INI-FILE (ini) style
Reading config file in HTTP-LIKE style
Creating config file in INI style

1) Reading/Updating config file in INI-FILE (ini) style

If the configuration file has different blocks, then this style is very useful
Let's explain with the below mentioned example

db_ini.cfg

[mysql]
host=DBI:mysql:host
login=mysql_user
password=mysql_pass
db_name=test
RaiseError=1
PrintError=1

[oracle]
host=DBI:oracle:host
login=oracle_user
password=oracle_pass
db_name=oracle_db
RaiseError=1
PrintError=1
  

Script

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use Config::Simple;

my $cfg = new Config::Simple('db_ini.cfg');

#Get Values from Config File
print "\n MySql DB Name     : " . $cfg->param("mysql.db_name");
print "\n MySql DB Password : " . $cfg->param("mysql.password");

print "\n\n Oracle DB Name     : " . $cfg->param("oracle.db_name");
print "\n Oracle DB Password : " . $cfg->param("oracle.password");
 
#Set/Update Values Config File
$cfg->param("mysql.db_name", "new_mysql_db_name");
$cfg->param("mysql.password", "new_mysql_password");

print "\n\n MySql DB Name     : " . $cfg->param("mysql.db_name");
print "\n MySql DB Password : " . $cfg->param("mysql.password");

$cfg->param("oracle.db_name", "new_orcl_db_name");
$cfg->param("oracle.password", "new_orcl_password");

print "\n\n Oracle DB Name     : " . $cfg->param("oracle.db_name");
print "\n Oracle DB Password : " . $cfg->param("oracle.password");

#Adding a new Variable to Config File
$cfg->param("mysql.new_var", "mysql_adding_variable");

print "\n\n MySql New Var     : " . $cfg->param("mysql.new_var");

$cfg->param("oracle.new_var", "oracle_adding_variable");

print "\n\n Oracle New Var     : " . $cfg->param("oracle.new_var");

print "\n\n Deleting Mysql New Var 'new_var' ... ";
$cfg->delete('mysql.new_var'); # deletes 'new_var' from [mysql] block

print "\n\n Deleting Oracle New Var 'new_var' ... ";
$cfg->delete('oracle.new_var'); # deletes 'new_var' from [oracle] block

#Config Vars
#Config::Simple also supports vars() method, which, depending on the context used, returns all the values either as hash or hashref
my %Config = $cfg->vars();
print "\n\n Config Hash Obj : " . Dumper(\%Config);

my $config_ref = $cfg->vars();
print "\n\n Config Hash Ref : " . Dumper($config_ref);
  

db_ini.cfg Output

 MySql DB Name     : test
 MySql DB Password : mysql_pass

 Oracle DB Name     : oracle_db
 Oracle DB Password : oracle_pass

 MySql DB Name     : new_mysql_db_name
 MySql DB Password : new_mysql_password

 Oracle DB Name     : new_orcl_db_name
 Oracle DB Password : new_orcl_password

 MySql New Var     : mysql_adding_variable

 Oracle New Var     : oracle_adding_variable

 Deleting Mysql New Var 'new_var' ... 
 
 Deleting Oracle New Var 'new_var' ... 
 
 Config Hash Obj : $VAR1 = {
          'mysql.PrintError' => '1',
          'mysql.db_name' => 'new_mysql_db_name',
          'oracle.password' => 'new_orcl_password',
          'oracle.host' => 'DBI:oracle:host',
          'mysql.host' => 'DBI:mysql:host',
          'mysql.password' => 'new_mysql_password',
          'oracle.PrintError' => '1',
          'oracle.login' => 'oracle_user',
          'mysql.RaiseError' => '1',
          'oracle.db_name' => 'new_orcl_db_name',
          'oracle.RaiseError' => '1',
          'mysql.login' => 'mysql_user'
        };


 Config Hash Ref : $VAR1 = {
          'mysql.PrintError' => '1',
          'oracle.password' => 'new_orcl_password',
          'mysql.db_name' => 'new_mysql_db_name',
          'oracle.host' => 'DBI:oracle:host',
          'mysql.host' => 'DBI:mysql:host',
          'oracle.PrintError' => '1',
          'mysql.password' => 'new_mysql_password',
          'oracle.login' => 'oracle_user',
          'mysql.RaiseError' => '1',
          'oracle.db_name' => 'new_orcl_db_name',
          'oracle.RaiseError' => '1',
          'mysql.login' => 'mysql_user'
        };
  

2) Reading/Updating config file in HTTP-LIKE style

When we just key and value pairs, this simple HTTP-Like style works.
Let's explain with the below mentioned example

db_http.cfg

host:'DBI:mysql:host'
login:user
password:secret
db_name:test
RaiseError:1
PrintError:1
  

Script

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use Config::Simple;

my $cfg = new Config::Simple('db_http.cfg');

#Get Values from Config File
print "\n DB Name     : " . $cfg->param("db_name");
print "\n DB Password : " . $cfg->param("password");
 
#Set/Update Values Config File
$cfg->param("db_name", "new_db_name");
$cfg->param("password", "new_password");

print "\n\n DB Name     : " . $cfg->param("db_name");
print "\n DB Password : " . $cfg->param("password");

#Adding a new Variable to Config File
$cfg->param("new_var", "adding_variable");

print "\n\n New Var     : " . $cfg->param("new_var");

print "\n\n Deleting New Var 'new_var' ... ";
$cfg->delete('new_var'); # deletes 'new_var'

#Config Vars
#Config::Simple also supports vars() method, which, depending on the context used, returns all the values either as hash or hashref
my %Config = $cfg->vars();
print "\n\n Config Hash Obj : " . Dumper(\%Config);

my $config_ref = $cfg->vars();
print "\n\n Config Hash Ref : " . Dumper($config_ref);

db_http.cfg Output

 DB Name     : test
 DB Password : secret

 DB Name     : new_db_name
 DB Password : new_password

 New Var     : adding_variable

 Deleting New Var 'new_var' ... 
 
 Config Hash Obj : $VAR1 = {
          'db_name' => 'new_db_name',
          'password' => 'new_password',
          'RaiseError' => '1',
          'PrintError' => '1',
          'login' => 'user',
          'host' => 'DBI:mysql:host'
        };

 Config Hash Ref : $VAR1 = {
          'db_name' => 'new_db_name',
          'password' => 'new_password',
          'RaiseError' => '1',
          'host' => 'DBI:mysql:host',
          'login' => 'user',
          'PrintError' => '1'
        };
  

3) Creating config file in INI style

Creating a config file is explained as mentioned below.

$cfg = new Config::Simple(syntax=>'ini');
$cfg->write("test.cfg");

Supported "syntax" keywords are "ini", "simple" or "http"

write()
Alternatively, you can pass a name to either write() or save() to indicate the name of the file to create instead of modifying existing configuration file

Since we are trying to create a new config file, we need to pass the file name.

Script

$cfg = new Config::Simple(syntax=>'ini');

$cfg->param("mysql.dsn", "DBI:mysql:db;host=localhost.com");
$cfg->param("mysql.user", "username");
$cfg->param("mysql.pass", 'secret');
$cfg->write("test.cfg");
  

test.cfg Output

[mysql]
dsn:mysql:db;host=localhost.com
user:username
pass:secret
  

Perl Remove Special Characters From File

While reading some kind of log files as mentioned below, we need to get rid of these special characters.

Because of these special characters, it makes the Developers job tough :
To parse the content of a file
To convert the special characters from the file

Let us explain how can we get rid of these special characters with a simple example

test.log

^[[1;31mTest 1^[[0m
^[[1;31mTest 2^[[0m
^[[1;31mTest 3^[[0m
^[[1;31mTest 4^[[0m
^[[1;31mTest 5^[[0m  

In the above test.log file, first of all, what is displayed as ^[ is not ^ and [
But it is the ASCII ESC character, produced by Esc or Ctrl[ (the ^ notation means the Ctrl key).

We can use the following regular expression :

s/\e\[[\d;]*[a-zA-Z]//g;

Note: 
\e represents escape character in the above regular expression (substituting instead of ^[ )
We can shorten from [a-zA-Z] to just [mK], based on the requirement
You can make use of the above regular expression while parsing the file as well (line by line)

In case if you want to backup file (test.log.bak) instead of changing in the original file (test.log) then use the following :
perl -pi.bak -e 's/\e\[[\d;]*[a-zA-Z]//g' test.log

The following will remove the special chars in test.log
perl -pi -e 's/\e\[[\d;]*[a-zA-Z]//g' test.log

Output after removing

Test 1
Test 2
Test 3
Test 4
Test 5
  

Unit Testing in Perl

We can write test scripts in Perl using Test::Simple and Test::More in easy way.

Test::More is an yet another framework for writing test scripts

Lets explain Test::More module with examples.

ok() vs is() 

1) Similar to ok(), is() and isnt() compare their two arguments with eq and ne respectively and use the result of that to determine if the test succeeded or failed. 

is($hsh{a}, 200, 'Test 200');
isnt($hsh{a}, 200, 'Test 200');

are similar to these:

ok($hsh{a} eq 200, 'Test 200');
ok($hsh{a} ne 200, 'Test 200');

2) They produce better diagnostics on failure. 
ok() cannot know what you are testing for (beyond the name)
but 
is() and isnt() know what the test was and why it failed. 

In case of test fail, ok() shows fail like below :
ok($hsh{a} == 200, 'Test 200');
# not ok 5 - Fail
#   Failed test 'Fail'
#   at main.pl line 21.

In case of test fail, is() or isnt() shows fail like below :
is($hsh{a}, 200, 'Test 200');
# not ok 5 - Fail
#   Failed test 'Fail'
#   at main.pl line 20.
#          got: '100'
#     expected: '200'

like()
like() allows to use regular exporessions in writing test cases
The following example, we are trying to check $str contains string 'freedom' or not

like($str, qr/freedom/i, 'String contains Freedom - ignore case');
ok($str =~ /freedom/i, 'String contains Freedom - ignore case');


cmp_ok()
cmp_ok() also useful in those cases where you are giving explicit conditions like >=, <=, ==, != etc.,

cmp_ok($scalar, "<=", 200, '10 is less than or equal to 200 - pass');
cmp_ok($scalar, "==", 10, '10 is equal to 10 - pass');

can_ok()

Syntax:
can_ok($module, @methods);
can_ok($object, @methods);

can_ok checks if a mthod exists in an object, here $obj is the object of "support" class
can_ok also checks if a method exists in an class, here "support" is the class
can_ok is good at taking mutiples methods to test at one shot

E.g.,
can_ok($obj, "add");
can_ok("support", "multiply");
can_ok("support", qw(test add multiply));

Lets explain the above methods with an example :
In the following example, we use support.pm for testing object, class and methods

support.pm

#!/usr/bin/perl

package support;

use strict;
use warnings;
use Data::Dumper;

sub new {
    my($class) = shift;
        
    my($self) = {};

    return(bless($self, $class));
}


sub multiply {
  my $a = shift;
  my $b = shift;
 
  return ($a*$b);
}  

sub add {
  my $a = shift;
  my $b = shift;
 
  return ($a+$b);
}  

sub test {
    print "\n test mehthod inside support package"; 
}  

1;  

main.pl

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use Test::More tests=>20;
use support;

my $obj = new support;

#You usually want to test if the module you're testing loads ok, rather than just vomiting if its load fails. It's recommended that you run use_ok() inside a BEGIN block so its functions are exported at compile-time and prototypes are properly honored.
BEGIN { use_ok("CGI"); }

#print "\n Obj : " . Dumper($obj);


#Testing Packages and Objects -----------------------------------------------
#Testing an object belongs to a class or not
ok (defined($obj) && ref $obj eq 'support', 'support obj new worked');

#can_ok checks if a mthod exists in an object, here $obj is the object of "support" class
#can_ok also checks if a method exists in an class, here "support" is the class
#can_ok is good at taking mutiples methods to test at one shot
can_ok($obj, "add");
can_ok("support", "multiply");
can_ok("support", qw(test add multiply));


#isa_ok checks if an object belongs to a class or not
isa_ok($obj, 'support');


#Testing Values -----------------------------------------------
my $scalar = 10;
my %hsh    = (a=>100, b=>200, c=>300);
my $str    = 'Freedom lies in being bold';


#is() vs ok()
#is() is recommended over ok()
#ok() function doesn't provide good diagnostic output.
#ok() cannot know what you are testing for (beyond the name), but is() and isnt() know what the test was and why it failed.

ok($scalar == 10, 'Pass');
is($scalar, 10, 'Pass');

is($hsh{a}, 100, 'Pass');
ok($hsh{a} == 100, 'Pass');

#is($hsh{a}, 200, 'Fail');
# not ok 5 - Fail
#   Failed test 'Fail'
#   at main.pl line 20.
#          got: '100'
#     expected: '200'

#ok($hsh{a} == 200, 'Fail');
# not ok 5 - Fail
#   Failed test 'Fail'
#   at main.pl line 21.

isnt($scalar, 20, 'Pass');

#like() allows to use regular exporessions in writing test cases
like($str, qr/freedom/i, 'String contains Freedom - ignore case');
ok($str =~ /freedom/i, 'String contains Freedom - ignore case');

#It's also useful in those cases where you are comparing numbers and applying conditions
cmp_ok($scalar, "<=", 200, '10 is less than or equal to 200 - pass');
cmp_ok($scalar, "==", 10, '10 is equal to 10 - pass');

Output:

1..20
ok 1 - use CGI;
ok 2 - support obj new worked
ok 3 - support->can('add')
ok 4 - support->can('multiply')
ok 5 - support->can(...)
ok 6 - The object isa support
ok 7 - Pass
ok 8 - Pass
ok 9 - Pass
ok 10 - Pass
ok 11 - Pass
ok 12 - String contains Freedom - ignore case
ok 13 - String contains Freedom - ignore case
ok 14 - 10 is less than or equal to 200 - pass
ok 15 - 10 is equal to 10 - pass
# Looks like you planned 20 tests but ran 15.
  

Perl Debug

Perl Debug is simple tool to easily debug perl scripts.

Few people like me find it difficult using Debug, but to be frank this is quite simple and straight forward. It makes the life of programmer easy to trace the bugs in a fast mode.

Without this, programmer needs to write unnecessary Print statements inside code and check where exactly things going wrong.

If you invoke Perl with the -d switch, your script runs under the Perl source debugger.

This works like an interactive Perl environment, prompting for debugger commands that let you examine source code, set breakpoints, dynamically pass the values of variables, etc.

This is so convenient that you often fire up the debugger all by itself just to test out Perl constructs interactively.

Debug Interactively:
Andrew E. Page, written an useful CPAN module Devel::Ptkdb, using this we can debug interactively.

This makes life much easier, no need to use <debug> prompt instead one can use the interactive mode to set the break points and pass the values to arguments dynamically.


How to Debug Perl Script Interactively using above module
perl -d:ptkdb myscript.pl  (for graphical representation of debugging)

Normal Debugger
perl debugger works using -d switch
Once you execute script using -d switch, it will change to debug prompt as mentioned below :
DB<1> ....
DB<2> ....

Some commonly used commands in Debug mode:

1) "s"  (Stepping through line by line execution) 
Keep pressing "s" will execute line by line

2) "l"  (List line) 
e.g.,
l 20                   #Lists line 20
l 20-25             #Lists 20 to 25 lines of script
l <subroutine>   #Lists a sub-routine

3) "b" (Setting break point on subroutine)
    "b" <subroutine>  
     #This will allow you to set a break point (set a break point on first line of subroutine)

4) "c" <subrutine>    
#This will take you directly to that break point (set one-time bkpt at subname and continue)

5) "q"                         
#It will quit  the debugger