<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
a	O
usage	B-Protocol
message	I-Protocol
or	O
help	O
message	O
refers	O
to	O
a	O
brief	O
message	O
displayed	O
by	O
a	O
program	O
that	O
utilizes	O
a	O
command-line	B-Application
interface	I-Application
for	O
execution	O
.	O
</s>
<s>
This	O
message	O
usually	O
consists	O
of	O
the	O
correct	O
command	B-Application
line	I-Application
usage	O
for	O
the	O
program	O
and	O
includes	O
a	O
list	O
of	O
the	O
correct	O
command-line	B-Application
arguments	O
or	O
options	O
acceptable	O
to	O
said	O
program	O
.	O
</s>
<s>
Usage	B-Protocol
messages	I-Protocol
are	O
utilized	O
as	O
a	O
quick	O
way	O
for	O
a	O
program	O
to	O
inform	O
the	O
user	O
of	O
proper	O
command	O
syntax	B-Application
,	O
and	O
should	O
not	O
be	O
substituted	O
for	O
proper	O
error	O
messages	O
or	O
for	O
detailed	O
documentation	O
such	O
as	O
a	O
man	B-Protocol
page	I-Protocol
.	O
</s>
<s>
On	O
Unix-like	O
platforms	O
,	O
usage	B-Protocol
messages	I-Protocol
usually	O
follow	O
the	O
same	O
common	O
pattern	O
:	O
</s>
<s>
Here	O
is	O
an	O
example	O
based	O
on	O
the	O
NetBSD	B-Device
:	O
</s>
<s>
To	O
print	O
a	O
usage	O
statement	O
in	O
a	O
shell	B-Language
script	I-Language
,	O
one	O
might	O
write	O
:	O
</s>
<s>
A	O
usage	O
statement	O
should	O
only	O
be	O
printed	O
when	O
specifically	O
requested	O
by	O
the	O
user	O
(	O
via	O
—	O
help	O
,	O
or	O
-h	O
,	O
or	O
-	O
?,	O
or	O
some	O
similar	O
flag	O
or	O
argument	O
)	O
and	O
should	O
be	O
written	O
to	O
the	O
standard	O
output	O
;	O
if	O
the	O
user	O
has	O
entered	O
an	O
incorrect	O
command	B-Application
line	I-Application
,	O
a	O
properly	O
written	O
command	B-Application
line	I-Application
program	O
will	O
print	O
a	O
succinct	O
error	O
message	O
that	O
describes	O
the	O
exact	O
error	O
made	O
by	O
the	O
user	O
rather	O
than	O
printing	O
the	O
usage	O
statement	O
and	O
requiring	O
the	O
user	O
to	O
figure	O
out	O
what	O
the	O
mistake	O
was	O
.	O
</s>
