<s>
join	O
is	O
a	O
command	B-Application
in	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
that	O
merges	O
the	O
lines	O
of	O
two	O
sorted	O
text	B-General_Concept
files	I-General_Concept
based	O
on	O
the	O
presence	O
of	O
a	O
common	O
field	B-Application
.	O
</s>
<s>
It	O
is	O
similar	O
to	O
the	O
join	O
operator	O
used	O
in	O
relational	B-Application
databases	I-Application
but	O
operating	O
on	O
text	B-General_Concept
files	I-General_Concept
.	O
</s>
<s>
The	O
join	O
command	B-Application
takes	O
as	O
input	O
two	O
text	B-General_Concept
files	I-General_Concept
and	O
a	O
number	O
of	O
options	O
.	O
</s>
<s>
If	O
no	O
command-line	O
argument	O
is	O
given	O
,	O
this	O
command	B-Application
looks	O
for	O
a	O
pair	O
of	O
lines	O
from	O
the	O
two	O
files	O
having	O
the	O
same	O
first	O
field	B-Application
(	O
a	O
sequence	O
of	O
characters	O
that	O
are	O
different	O
from	O
space	O
)	O
,	O
and	O
outputs	O
a	O
line	O
composed	O
of	O
the	O
first	O
field	B-Application
followed	O
by	O
the	O
rest	O
of	O
the	O
two	O
lines	O
.	O
</s>
<s>
The	O
program	O
arguments	O
specify	O
which	O
character	O
to	O
be	O
used	O
in	O
place	O
of	O
space	O
to	O
separate	O
the	O
fields	O
of	O
the	O
line	O
,	O
which	O
field	B-Application
to	O
use	O
when	O
looking	O
for	O
matching	O
lines	O
,	O
and	O
whether	O
to	O
output	O
lines	O
that	O
do	O
not	O
match	O
.	O
</s>
<s>
The	O
output	O
can	O
be	O
stored	O
to	O
another	O
file	O
rather	O
than	O
printing	O
using	O
redirection	B-Device
.	O
</s>
<s>
Both	O
files	O
have	O
been	O
sorted	O
on	O
the	O
join	O
field	B-Application
—	O
this	O
is	O
a	O
requirement	O
of	O
the	O
program	O
.	O
</s>
<s>
It	O
was	O
inherited	O
into	O
the	O
first	O
version	O
of	O
POSIX.1	O
and	O
the	O
Single	O
Unix	B-Application
Specification	O
.	O
</s>
<s>
The	O
version	O
of	O
join	O
bundled	O
in	O
GNU	B-Application
coreutils	I-Application
was	O
written	O
by	O
Mike	O
Haertel	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
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>
