<s>
Plack	B-Language
is	O
a	O
Perl	B-Language
web	B-Application
application	I-Application
programming	I-Application
framework	I-Application
inspired	O
by	O
Rack	B-Application
for	O
Ruby	B-Language
and	O
WSGI	B-Language
for	O
Python	B-Language
,	O
and	O
it	O
is	O
the	O
project	O
behind	O
the	O
PSGI	O
specification	O
used	O
by	O
other	O
frameworks	B-Application
such	O
as	O
Catalyst	B-Language
and	O
Dancer	B-Language
.	O
</s>
<s>
Plack	B-Language
allows	O
for	O
testing	O
of	O
Perl	B-Language
web	B-Application
applications	I-Application
without	O
a	O
live	O
web	B-Application
server	I-Application
.	O
</s>
<s>
Plackup	O
is	O
a	O
command	B-Device
line	I-Device
utility	I-Device
to	O
run	O
PSGI	O
applications	O
from	O
the	O
command	O
line	O
.	O
</s>
<s>
PSGI	O
or	O
Perl	B-Language
Web	I-Language
Server	I-Language
Gateway	I-Language
Interface	I-Language
is	O
an	O
interface	B-Application
between	O
web	B-Application
servers	I-Application
and	O
web	B-Application
applications	I-Application
and	O
frameworks	B-Application
written	O
in	O
the	O
Perl	B-Language
programming	I-Language
language	I-Language
that	O
allows	O
writing	O
portable	O
applications	O
that	O
can	O
be	O
run	O
as	O
standalone	O
servers	O
or	O
using	O
CGI	B-Language
,	O
FastCGI	O
,	O
mod_perl	O
,	O
et	O
al	O
.	O
</s>
<s>
It	O
is	O
inspired	O
by	O
the	O
Web	B-Language
Server	I-Language
Gateway	I-Language
Interface	I-Language
for	O
Python	B-Language
,	O
Rack	B-Application
for	O
Ruby	B-Language
and	O
JSGI	B-Language
for	O
JavaScript	B-Language
.	O
</s>
<s>
A	O
PSGI	O
application	O
is	O
a	O
Perl	B-Language
subroutine	O
that	O
accepts	O
arguments	O
as	O
a	O
single	O
hash	O
reference	O
and	O
returns	O
a	O
reference	O
to	O
an	O
array	O
of	O
three	O
elements	O
:	O
an	O
HTTP	B-Protocol
status	I-Protocol
code	I-Protocol
,	O
a	O
reference	O
to	O
an	O
array	O
of	O
HTTP	B-Protocol
headers	I-Protocol
and	O
a	O
reference	O
to	O
an	O
array	O
of	O
HTTP	O
body	O
lines	O
(	O
usually	O
a	O
generated	O
HTML	B-Language
document	O
)	O
or	O
a	O
filehandle-like	O
object	O
.	O
</s>
<s>
Plack	B-Language
supports	O
the	O
following	O
server	O
backends	O
:	O
</s>
<s>
Using	O
the	O
default	O
standalone	O
HTTP	B-Application
server	I-Application
:	O
</s>
<s>
Running	O
as	O
a	O
FastCGI	O
daemon	B-Operating_System
listening	O
on	O
a	O
Unix	B-Protocol
socket	I-Protocol
,	O
ready	O
to	O
be	O
used	O
by	O
any	O
Web	B-Application
server	I-Application
with	O
FastCGI	O
support	O
:	O
</s>
<s>
A	O
working	O
Hello	O
world	O
application	O
run	O
as	O
a	O
one-liner	B-Language
:	O
</s>
<s>
The	O
command	O
above	O
starts	O
an	O
HTTP	B-Application
server	I-Application
listening	O
on	O
port	B-Protocol
5000	O
of	O
every	O
local	O
interface	B-Application
(	O
IP	B-Protocol
address	I-Protocol
)	O
and	O
returns	O
this	O
200	O
OK	O
response	O
to	O
every	O
HTTP	O
request	O
:	O
</s>
