<s>
A	O
Perl	B-Language
module	I-Language
is	O
a	O
discrete	O
component	O
of	O
software	O
for	O
the	O
Perl	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
Technically	O
,	O
it	O
is	O
a	O
particular	O
set	O
of	O
conventions	O
for	O
using	O
Perl	B-Language
's	O
package	O
mechanism	O
that	O
has	O
become	O
universally	O
adopted	O
.	O
</s>
<s>
A	O
module	B-Language
defines	O
its	O
source	O
code	O
to	O
be	O
in	O
a	O
package	O
(	O
much	O
like	O
a	O
Java	B-Language
package	I-Language
)	O
,	O
the	O
Perl	B-Language
mechanism	O
for	O
defining	O
namespaces	O
,	O
e.g.	O
</s>
<s>
Furthermore	O
,	O
a	O
module	B-Language
is	O
the	O
Perl	B-Language
equivalent	O
of	O
the	O
class	O
when	O
object-oriented	B-Language
programming	I-Language
is	O
employed	O
.	O
</s>
<s>
A	O
collection	O
of	O
modules	B-Language
,	O
with	O
accompanying	O
documentation	O
,	O
build	B-Application
scripts	I-Application
,	O
and	O
usually	O
a	O
test	O
suite	O
,	O
composes	O
a	O
distribution	O
.	O
</s>
<s>
The	O
Perl	B-Language
community	O
has	O
a	O
sizable	O
library	O
of	O
distributions	O
available	O
for	O
search	O
and	O
download	O
via	O
CPAN	B-Language
.	O
</s>
<s>
Perl	B-Language
is	O
a	O
language	O
allowing	O
many	O
different	O
styles	O
of	O
programming	O
.	O
</s>
<s>
A	O
developer	O
is	O
as	O
likely	O
to	O
find	O
a	O
module	B-Language
written	O
in	O
a	O
procedural	B-Application
style	O
(	O
for	O
example	O
,	O
)	O
as	O
object-oriented	B-Language
(	O
e.g.	O
</s>
<s>
)	O
,	O
both	O
are	O
considered	O
equally	O
valid	O
according	O
to	O
what	O
the	O
module	B-Language
needs	O
to	O
do	O
.	O
</s>
<s>
Modules	B-Language
might	O
also	O
be	O
used	O
to	O
mixin	B-Language
methods	O
(	O
)	O
or	O
be	O
a	O
pragma	O
(	O
)	O
which	O
has	O
an	O
effect	O
immediately	O
upon	O
being	O
loaded	O
.	O
</s>
<s>
Modules	B-Language
can	O
even	O
be	O
used	O
to	O
alter	O
the	O
syntax	O
of	O
the	O
language	O
.	O
</s>
<s>
The	O
effect	O
of	O
Perl	B-Language
modules	I-Language
are	O
usually	O
limited	O
to	O
the	O
current	O
scope	B-Language
in	O
which	O
it	O
was	O
loaded	O
.	O
</s>
<s>
It	O
is	O
common	O
for	O
Perl	B-Language
modules	I-Language
to	O
have	O
embedded	O
documentation	O
in	O
Perl	B-Language
's	O
Plain	B-Language
Old	I-Language
Documentation	I-Language
format	O
.	O
</s>
<s>
Contrast	O
with	O
javadoc	B-Language
which	O
is	O
specialized	O
to	O
documenting	O
Java	B-Language
classes	O
.	O
</s>
<s>
By	O
convention	O
,	O
module	B-Language
documentation	O
typically	O
follows	O
the	O
structure	O
of	O
a	O
Unix	B-Protocol
man	I-Protocol
page	I-Protocol
.	O
</s>
<s>
The	O
language	O
of	O
Perl	B-Language
is	O
defined	O
by	O
the	O
single	O
implementation	O
(	O
referred	O
to	O
as	O
"	O
perl	B-Language
"	O
)	O
and	O
is	O
added	O
to	O
(	O
and	O
in	O
rare	O
occasions	O
taken	O
away	O
from	O
)	O
each	O
new	O
release	O
.	O
</s>
<s>
For	O
this	O
reason	O
it	O
is	O
important	O
for	O
a	O
module	B-Language
author	O
to	O
be	O
aware	O
what	O
features	O
they	O
're	O
making	O
use	O
of	O
and	O
what	O
the	O
minimum	O
required	O
version	O
of	O
perl	B-Language
is	O
.	O
</s>
<s>
The	O
code	O
on	O
this	O
page	O
requires	O
perl	B-Language
5.6.0	O
which	O
is	O
considered	O
rather	O
old	O
by	O
now	O
.	O
</s>
<s>
What	O
follows	O
are	O
examples	O
of	O
"	O
Hello	O
,	O
World	O
"	O
implemented	O
in	O
different	O
styles	O
of	O
modules	B-Language
.	O
</s>
<s>
It	O
must	O
be	O
understood	O
that	O
a	O
module	B-Language
is	O
not	O
necessary	O
in	O
Perl	B-Language
;	O
functions	O
and	O
code	O
can	O
be	O
defined	O
and	O
used	O
anywhere	O
.	O
</s>
<s>
Contrast	O
with	O
Java	B-Language
where	O
a	O
class	O
is	O
always	O
necessary	O
.	O
</s>
<s>
Here	O
is	O
"	O
Hello	O
,	O
World	O
"	O
implemented	O
as	O
a	O
procedural	B-Application
module	B-Language
with	O
a	O
customizable	O
target	O
for	O
the	O
greeting	O
,	O
just	O
to	O
make	O
things	O
interesting	O
.	O
</s>
<s>
Also	O
included	O
is	O
a	O
short	O
script	O
to	O
illustrate	O
the	O
module	B-Language
's	O
use	O
.	O
</s>
<s>
A	O
running	O
Perl	B-Language
program	O
has	O
a	O
built-in	O
namespace	O
called	O
"	O
main	O
"	O
,	O
which	O
is	O
the	O
default	O
name	O
.	O
</s>
<s>
Package	O
declarations	O
apply	O
package	O
scope	B-Language
till	O
the	O
next	O
package	O
declaration	O
or	O
the	O
end	O
of	O
the	O
block	O
in	O
which	O
the	O
declaration	O
is	O
made	O
.	O
</s>
<s>
Conventionally	O
,	O
namespaces	O
are	O
associated	O
with	O
modules	B-Language
;	O
in	O
practice	O
,	O
there	O
is	O
usually	O
one	O
namespace	O
per	O
module	B-Language
and	O
vice	O
versa	O
,	O
but	O
that	O
's	O
not	O
mandated	O
by	O
the	O
language	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
'	O
standard	O
 '	O
module	B-Language
CGI.pm	O
has	O
the	O
following	O
declaration	O
at	O
its	O
top	O
:	O
</s>
<s>
This	O
module	B-Language
,	O
and	O
its	O
functionality	O
,	O
would	O
commonly	O
be	O
invoked	O
as	O
follows	O
:	O
</s>
