<s>
Server	O
Side	O
Includes	O
(	O
SSI	O
)	O
is	O
a	O
simple	O
interpreted	O
server-side	B-Language
scripting	I-Language
language	O
used	O
almost	O
exclusively	O
for	O
the	O
World	O
Wide	O
Web	O
.	O
</s>
<s>
It	O
is	O
most	O
useful	O
for	O
including	O
the	O
contents	O
of	O
one	O
or	O
more	O
files	O
into	O
a	O
web	O
page	O
on	O
a	O
web	B-Application
server	I-Application
(	O
see	O
below	O
)	O
,	O
using	O
its	O
#include	O
directive	O
.	O
</s>
<s>
It	O
is	O
supported	O
by	O
Apache	B-Application
,	O
LiteSpeed	B-Protocol
,	O
nginx	B-Operating_System
,	O
IIS	B-Application
as	O
well	O
as	O
W3C	O
's	O
Jigsaw	O
.	O
</s>
<s>
It	O
has	O
its	O
roots	O
in	O
NCSA	B-Application
HTTPd	I-Application
.	O
</s>
<s>
In	O
order	O
for	O
a	O
web	B-Application
server	I-Application
to	O
recognize	O
an	O
SSI-enabled	O
HTML	B-Language
file	I-Language
and	O
therefore	O
carry	O
out	O
these	O
instructions	O
,	O
either	O
the	O
filename	O
should	O
end	O
with	O
a	O
special	O
extension	O
,	O
by	O
default	O
.shtml	O
,	O
.stm	O
,	O
.shtm	O
,	O
or	O
,	O
if	O
the	O
server	O
is	O
configured	O
to	O
allow	O
this	O
,	O
set	O
the	O
execution	O
bit	O
of	O
the	O
file	O
.	O
</s>
<s>
Its	O
control	O
flow	O
is	O
rather	O
simple	O
,	O
choice	O
is	O
supported	O
,	O
but	O
loops	O
are	O
not	O
natively	O
supported	O
and	O
can	O
only	O
be	O
done	O
by	O
recursion	O
using	O
include	O
or	O
using	O
HTTP	B-Protocol
redirect	O
.	O
</s>
<s>
The	O
simple	O
design	O
of	O
the	O
language	O
makes	O
it	O
easier	O
to	O
learn	O
and	O
use	O
than	O
most	O
server-side	B-Language
scripting	I-Language
languages	O
,	O
while	O
complicated	O
server-side	O
processing	O
is	O
often	O
done	O
with	O
one	O
of	O
the	O
more	O
feature-rich	O
programming	O
languages	O
.	O
</s>
<s>
SSI	O
is	O
Turing	B-Algorithm
complete	I-Algorithm
.	O
</s>
<s>
Directives	O
are	O
placed	O
in	O
HTML	B-Language
comments	O
so	O
that	O
if	O
SSI	O
is	O
not	O
enabled	O
,	O
users	O
will	O
not	O
see	O
the	O
SSI	O
directives	O
on	O
the	O
page	O
,	O
unless	O
they	O
look	O
at	O
its	O
source	O
.	O
</s>
<s>
Apache	B-Application
tutorial	O
on	O
SSI	O
stipulates	O
the	O
format	O
requires	O
a	O
space	O
character	O
before	O
the	O
"	O
-->	O
 "	O
that	O
closes	O
the	O
element	O
.	O
</s>
<s>
The	O
following	O
are	O
SSI	O
directives	O
from	O
the	O
times	O
of	O
NCSA	B-Application
HTTPd	I-Application
(	O
the	O
1990s	O
)	O
.	O
</s>
<s>
The	O
file	O
or	O
virtual	O
parameters	O
specify	O
the	O
file	O
(	O
HTML	B-Language
page	O
,	O
text	O
file	O
,	O
script	O
,	O
etc	O
.	O
)	O
</s>
<s>
NCSA	B-Application
HTTPd	I-Application
did	O
not	O
support	O
CGI	B-Language
via	O
include	O
,	O
but	O
later	O
Apache	B-Application
HTTPd	I-Application
does	O
.	O
</s>
<s>
The	O
Apache	B-Application
documentation	O
recommends	O
using	O
"	O
virtual	O
"	O
in	O
preference	O
to	O
"	O
file	O
"	O
.	O
</s>
<s>
<!--#include file="footer.html" --></nowiki>	O
exec	O
cgi	B-Language
or	O
cmd	O
This	O
directive	O
executes	O
a	O
program	O
,	O
script	O
,	O
or	O
shell	O
command	O
on	O
the	O
server	O
.	O
</s>
<s>
The	O
cmd	O
parameter	O
specifies	O
a	O
server-side	O
command	O
;	O
the	O
cgi	B-Language
parameter	O
specifies	O
the	O
path	O
to	O
a	O
CGI	B-Language
script	I-Language
.	O
</s>
<s>
<!--#exec cmd="ls -l" --></nowiki>	O
echo	O
var	O
This	O
directive	O
displays	O
the	O
contents	O
of	O
a	O
specified	O
HTTP	B-Protocol
environment	O
variable	O
.	O
</s>
<s>
Apache	B-Application
provides	O
additional	O
parameters	O
for	O
encodings	B-Algorithm
.	O
</s>
<s>
<nowiki><!--#set var="foo" value="bar" --></nowiki>	O
Apache	B-Application
,	O
Nginx	B-Operating_System
printenv	O
This	O
directive	O
outputs	O
a	O
list	O
of	O
all	O
SSI	O
variables	O
and	O
their	O
values	O
,	O
including	O
environmental	O
and	O
user-defined	O
variables	O
.	O
</s>
