<s>
uniq	B-Application
is	O
a	O
utility	O
command	B-Application
on	O
Unix	B-Application
,	O
Plan	B-Operating_System
9	I-Operating_System
,	O
Inferno	B-Operating_System
,	O
and	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
which	O
,	O
when	O
fed	O
a	O
text	B-General_Concept
file	I-General_Concept
or	O
standard	O
input	O
,	O
outputs	O
the	O
text	O
with	O
adjacent	O
identical	O
lines	O
collapsed	O
to	O
one	O
,	O
unique	O
line	O
of	O
text	O
.	O
</s>
<s>
The	O
command	B-Application
is	O
a	O
kind	O
of	O
filter	O
program	O
.	O
</s>
<s>
It	O
can	O
also	O
output	O
only	O
the	O
duplicate	O
lines	O
(	O
with	O
the	O
-d	O
option	O
)	O
,	O
or	O
add	O
the	O
number	O
of	O
occurrences	O
of	O
each	O
line	O
(	O
with	O
the	O
-c	O
option	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
following	O
command	B-Application
lists	O
the	O
unique	O
lines	O
in	O
a	O
file	O
,	O
sorted	O
by	O
the	O
number	O
of	O
times	O
each	O
occurs	O
:	O
</s>
<s>
Using	O
uniq	B-Application
like	O
this	O
is	O
common	O
when	O
building	O
pipelines	B-Operating_System
in	O
shell	B-Language
scripts	I-Language
.	O
</s>
<s>
First	O
appearing	O
in	O
Version	B-Operating_System
3	I-Operating_System
Unix	I-Operating_System
,	O
uniq	B-Application
is	O
now	O
available	O
for	O
a	O
number	O
of	O
different	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
It	O
was	O
inherited	O
into	O
the	O
first	O
version	O
of	O
POSIX	O
and	O
the	O
Single	O
Unix	B-Application
Specification	O
.	O
</s>
<s>
The	O
version	O
bundled	O
in	O
GNU	B-Application
coreutils	I-Application
was	O
written	O
by	O
Richard	O
Stallman	O
and	O
David	O
MacKenzie	O
.	O
</s>
<s>
A	O
uniq	B-Application
command	B-Application
is	O
also	O
part	O
of	O
ASCII	O
's	O
MSX-DOS2	O
Tools	O
for	O
MSX-DOS	B-Operating_System
version	O
2	O
.	O
</s>
<s>
The	O
command	B-Application
is	O
available	O
as	O
a	O
separate	O
package	O
for	O
Microsoft	B-Application
Windows	I-Application
as	O
part	O
of	O
the	O
GnuWin32	B-Language
project	O
and	O
the	O
UnxUtils	B-Application
collection	O
of	O
native	B-Language
Win32	B-Library
ports	O
of	O
common	O
GNU	B-Operating_System
Unix-like	B-Operating_System
utilities	O
.	O
</s>
<s>
The	O
command	B-Application
has	O
also	O
been	O
ported	O
to	O
the	O
IBM	B-Application
i	I-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
