<s>
Google	B-Application
Code	I-Application
Search	I-Application
was	O
a	O
free	O
beta	O
product	O
from	O
Google	B-Application
which	O
debuted	O
in	O
Google	B-Application
Labs	I-Application
on	O
October	O
5	O
,	O
2006	O
,	O
allowing	O
web	O
users	O
to	O
search	O
for	O
open-source	O
code	O
on	O
the	O
Internet	O
.	O
</s>
<s>
The	O
code	O
available	O
for	O
searching	O
was	O
in	O
various	O
formats	O
including	O
tar.gz	O
,	O
.tar.bz2	O
,	O
.tar	O
,	O
and	O
.zip	O
,	O
CVS	B-Application
,	O
Subversion	B-Application
,	O
git	B-Application
and	O
Mercurial	B-Protocol
repositories	O
.	O
</s>
<s>
Google	B-Application
Code	I-Application
Search	I-Application
covered	O
many	O
open-source	O
projects	O
,	O
and	O
as	O
such	O
is	O
different	O
from	O
the	O
"	O
Code	O
Search	O
for	O
Google	B-Application
Open	O
source	O
projects	O
"	O
that	O
was	O
released	O
afterwards	O
.	O
</s>
<s>
The	O
site	O
allowed	O
the	O
use	O
of	O
regular	B-Language
expressions	I-Language
in	O
queries	O
,	O
which	O
at	O
that	O
time	O
was	O
not	O
offered	O
by	O
any	O
other	O
search	B-Application
engine	I-Application
for	O
code	O
.	O
</s>
<s>
This	O
makes	O
it	O
resemble	O
grep	B-Application
,	O
but	O
over	O
the	O
world	O
's	O
public	O
code	O
.	O
</s>
<s>
The	O
methodology	O
employed	O
,	O
sometimes	O
called	O
trigram	B-Algorithm
search	I-Algorithm
,	O
combines	O
a	O
trigram	B-General_Concept
index	B-Application
with	O
a	O
custom-built	O
,	O
denial-of-service	B-Algorithm
resistant	O
regular	B-Language
expression	I-Language
engine	O
.	O
</s>
<s>
In	O
March	O
2010	O
,	O
the	O
code	O
of	O
RE2	B-Algorithm
,	O
the	O
regular	B-Language
expression	I-Language
engine	O
used	O
in	O
Google	B-Application
Code	I-Application
Search	I-Application
,	O
was	O
made	O
open	O
source	O
.	O
</s>
<s>
Google	B-Application
Code	I-Application
Search	I-Application
supported	O
POSIX	O
extended	O
regular	B-Language
expression	I-Language
syntax	O
,	O
excluding	O
back-references	O
,	O
collating	O
elements	O
,	O
and	O
collation	O
classes	O
.	O
</s>
<s>
In	O
October	O
2011	O
,	O
Google	B-Application
announced	O
that	O
Code	O
Search	O
was	O
to	O
be	O
shut	O
down	O
along	O
with	O
the	O
Code	O
Search	O
API	O
.	O
</s>
<s>
The	O
service	O
remained	O
online	O
until	O
March	O
2013	O
,	O
and	O
it	O
now	O
returns	O
a	O
404	B-Protocol
.	O
</s>
<s>
In	O
January	O
2012	O
,	O
Russ	O
Cox	O
published	O
an	O
overview	O
of	O
history	O
and	O
the	O
technical	O
aspects	O
of	O
the	O
tool	O
,	O
and	O
open-sourced	O
a	O
basic	O
implementation	O
of	O
a	O
similar	O
functionality	O
as	O
a	O
set	O
of	O
standalone	O
programs	O
that	O
can	O
run	O
fast	O
indexed	O
regular	B-Language
expression	I-Language
searches	O
over	O
local	O
code	O
.	O
</s>
