<s>
"	O
Bad	B-Application
command	I-Application
or	I-Application
file	I-Application
name	I-Application
"	O
is	O
a	O
common	O
and	O
ambiguous	O
error	B-Error_Name
message	I-Error_Name
in	O
MS-DOS	B-Application
and	O
some	O
other	O
operating	O
systems	O
.	O
</s>
<s>
COMMAND.COM	B-Operating_System
,	O
the	O
primary	O
user	O
interface	O
of	O
MS-DOS	B-Application
,	O
produces	O
this	O
error	B-Error_Name
message	I-Error_Name
when	O
the	O
first	O
word	O
of	O
a	O
command	O
could	O
not	O
be	O
interpreted	O
.	O
</s>
<s>
For	O
MS-DOS	B-Application
,	O
this	O
word	O
must	O
be	O
the	O
name	O
of	O
an	O
internal	O
command	O
,	O
executable	O
file	O
or	O
batch	O
file	O
,	O
so	O
the	O
error	B-Error_Name
message	I-Error_Name
provided	O
an	O
accurate	O
description	O
of	O
the	O
problem	O
but	O
easily	O
confused	O
novices	O
.	O
</s>
<s>
Later	O
,	O
the	O
wording	O
of	O
the	O
error	B-Error_Name
message	I-Error_Name
was	O
changed	O
for	O
clarity	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
displays	O
the	O
following	O
error	B-Error_Name
message	I-Error_Name
instead	O
(	O
where	O
"	O
foo	O
"	O
is	O
replaced	O
by	O
the	O
word	O
causing	O
error	O
)	O
:	O
</s>
<s>
Some	O
early	O
Unix	B-Application
shells	I-Application
produced	O
the	O
equally	O
cryptic	O
""	O
for	O
the	O
same	O
reasons	O
.	O
</s>
<s>
Most	O
modern	O
shells	O
produce	O
an	O
error	B-Error_Name
message	I-Error_Name
similar	O
to	O
""	O
.	O
</s>
