<s>
DIGITAL	B-Operating_System
Command	I-Operating_System
Language	I-Operating_System
(	O
DCL	O
)	O
is	O
the	O
standard	O
command	B-Language
language	I-Language
adopted	O
by	O
many	O
of	O
the	O
operating	B-General_Concept
systems	I-General_Concept
created	O
by	O
Digital	O
Equipment	O
Corporation	O
.	O
</s>
<s>
DCL	O
had	O
its	O
roots	O
in	O
IAS	B-Application
,	O
TOPS-20	B-Operating_System
,	O
and	O
RT-11	B-Operating_System
and	O
was	O
implemented	O
as	O
a	O
standard	O
across	O
most	O
of	O
Digital	O
's	O
operating	B-General_Concept
systems	I-General_Concept
,	O
notably	O
RSX-11	B-Application
and	O
RSTS/E	B-Operating_System
,	O
but	O
took	O
its	O
most	O
powerful	O
form	O
in	O
VAX/VMS	B-Operating_System
(	O
later	O
OpenVMS	B-Operating_System
)	O
.	O
</s>
<s>
DCL	O
continues	O
to	O
be	O
developed	O
by	O
VSI	O
as	O
part	O
of	O
OpenVMS	B-Operating_System
.	O
</s>
<s>
Written	O
when	O
the	O
programming	O
language	O
Fortran	B-Application
was	O
in	O
heavy	O
use	O
,	O
DCL	O
is	O
a	O
scripting	B-Language
language	I-Language
supporting	O
several	O
data	O
types	O
,	O
including	O
strings	O
,	O
integers	O
,	O
bit	O
arrays	O
,	O
arrays	O
and	O
booleans	O
,	O
but	O
not	O
floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
.	O
</s>
<s>
Access	O
to	O
OpenVMS	B-Operating_System
system	O
services	O
(	O
kernel	B-Operating_System
API	B-General_Concept
)	O
is	O
through	O
lexical	O
functions	O
,	O
which	O
perform	O
the	O
same	O
as	O
their	O
compiled	B-Language
language	I-Language
counterparts	O
and	O
allow	O
scripts	O
to	O
get	O
information	O
on	O
system	O
state	O
.	O
</s>
<s>
DCL	O
includes	O
IF-THEN-ELSE	B-Language
,	O
access	O
to	O
all	O
the	O
Record	B-Application
Management	I-Application
Services	I-Application
(	O
RMS	B-Application
)	O
file	O
types	O
including	O
stream	O
,	O
indexed	O
,	O
and	O
sequential	O
,	O
but	O
unfortunately	O
lacks	O
a	O
DO-WHILE	O
or	O
other	O
looping	O
construct	O
,	O
requiring	O
users	O
to	O
make	O
do	O
with	O
IF	O
and	O
GOTO-label	O
statements	O
instead	O
.	O
</s>
<s>
VCL	O
and	O
VX/DCL	O
for	O
Unix	B-Application
,	O
</s>
<s>
VCL	O
for	O
MS-DOS	B-Application
,	O
OS/2	B-Application
and	O
Windows	B-Application
,	O
</s>
<s>
and	O
Accelr8	O
DCL	O
Lite	O
for	O
Windows	B-Application
.	O
</s>
<s>
DCL	O
is	O
the	O
basis	O
of	O
the	O
XLNT	B-Language
language	O
,	O
implemented	O
on	O
Windows	B-Application
by	O
an	O
interpreter-IDE-WSH	O
engine	O
combination	O
with	O
CGI	O
capabilities	O
distributed	O
by	O
Advanced	O
System	O
Concepts	O
Inc	O
.	O
from	O
1997	O
.	O
</s>
<s>
For	O
the	O
OpenVMS	B-Operating_System
implementation	O
,	O
the	O
command	B-Application
line	I-Application
parser	O
is	O
a	O
runtime	O
library	B-Library
(	O
)	O
that	O
can	O
be	O
compiled	O
into	O
user	O
applications	O
and	O
therefore	O
gives	O
a	O
consistent	O
command	B-Application
line	I-Application
interface	I-Application
for	O
both	O
OS	O
supplied	O
commands	B-Application
and	O
user	O
written	O
commands	B-Application
.	O
</s>
<s>
The	O
command	B-Application
line	I-Application
must	O
start	O
with	O
a	O
verb	O
and	O
is	O
then	O
followed	O
by	O
up	O
to	O
8	O
parameters	O
(	O
arguments	O
)	O
and/or	O
qualifiers	O
(	O
switches	O
in	O
Unix	B-Application
terminology	O
)	O
which	O
begin	O
with	O
a	O
'	O
/	O
'	O
character	O
.	O
</s>
<s>
Unlike	O
Unix	B-Application
(	O
but	O
similar	O
to	O
DOS	B-Device
)	O
,	O
a	O
space	O
is	O
not	O
required	O
before	O
the	O
'	O
/	O
'	O
.	O
</s>
<s>
Qualifiers	O
can	O
be	O
position	O
independent	O
(	O
occurring	O
anywhere	O
on	O
the	O
command	B-Application
line	I-Application
)	O
or	O
position	O
dependent	O
,	O
in	O
which	O
case	O
the	O
qualifier	O
affects	O
the	O
parameter	O
it	O
appears	O
after	O
.	O
</s>
<s>
While	O
DCL	O
documentation	O
usually	O
shows	O
all	O
DCL	O
commands	B-Application
in	O
uppercase	O
,	O
DCL	O
commands	B-Application
are	O
case-insensitive	O
and	O
may	O
be	O
typed	O
in	O
upper-	O
,	O
lower-	O
,	O
or	O
mixed-case	O
.	O
</s>
<s>
Some	O
implementations	O
such	O
as	O
OpenVMS	B-Operating_System
used	O
a	O
minimum	O
uniqueness	O
scheme	O
in	O
allowing	O
commands	B-Application
to	O
be	O
shortened	O
while	O
others	O
such	O
as	O
RSX-11	B-Application
allowed	O
commands	B-Application
to	O
be	O
abbreviated	O
to	O
a	O
minimum	O
of	O
three	O
characters	O
.	O
</s>
<s>
Unlike	O
other	O
systems	O
which	O
use	O
paths	B-Application
for	O
locating	O
commands	B-Application
,	O
DCL	O
requires	O
commands	B-Application
to	O
be	O
defined	O
explicitly	O
,	O
either	O
via	O
CLD	O
(	O
Command	B-Language
Language	I-Language
Definition	O
)	O
definitions	O
or	O
a	O
foreign	O
symbol	O
.	O
</s>
<s>
Most	O
OpenVMS-native	O
commands	B-Application
are	O
defined	O
via	O
CLD	O
files	O
;	O
these	O
are	O
compiled	O
by	O
the	O
CDU	O
,	O
the	O
Command	O
Definition	O
Utility	O
,	O
and	O
added	O
to	O
a	O
DCL	O
'	O
table	O
 '	O
--	O
by	O
default	O
,	O
although	O
processes	O
are	O
free	O
to	O
use	O
their	O
own	O
tables	O
—	O
and	O
can	O
then	O
be	O
invoked	O
by	O
the	O
user	O
.	O
</s>
<s>
The	O
user	O
can	O
then	O
type	B-Device
""	O
,	O
or	O
""	O
,	O
and	O
the	O
FOO	O
program	O
will	O
be	O
invoked	O
.	O
</s>
<s>
The	O
command	O
definition	O
language	O
supports	O
many	O
types	O
of	O
options	O
,	O
for	O
example	O
dates	O
and	O
file	O
specifications	O
,	O
and	O
allows	O
a	O
qualifier	O
to	O
change	O
the	O
image	O
invoked	O
—	O
for	O
example	O
""	O
,	O
to	O
create	O
a	O
file	O
,	O
vs.	O
""	O
to	O
create	O
a	O
directory	B-Application
.	O
</s>
<s>
The	O
other	O
(	O
simpler	O
,	O
but	O
less	O
flexible	O
)	O
method	O
to	O
define	O
commands	B-Application
is	O
via	O
foreign	O
commands	B-Application
.	O
</s>
<s>
This	O
is	O
more	O
akin	O
to	O
the	O
Unix	B-Application
method	O
of	O
invoking	O
programs	O
.	O
</s>
<s>
This	O
method	O
is	O
generally	O
used	O
for	O
programs	O
ported	O
from	O
Unix	B-Application
and	O
other	O
non-native	O
systems	O
;	O
for	O
C	O
programs	O
using	O
argc	O
and	O
argv	O
command	O
syntax	O
.	O
</s>
<s>
Versions	O
of	O
OpenVMS	B-Operating_System
DCL	O
starting	O
with	O
V6.2	O
support	O
the	O
logical	O
name	O
for	O
establishing	O
Unix-style	O
command	O
paths	B-Application
.	O
</s>
<s>
allows	O
a	O
list	O
of	O
directories	B-Application
to	O
be	O
specified	O
,	O
and	O
these	O
directories	B-Application
are	O
then	O
searched	O
for	O
DCL	O
command	O
procedures	O
(	O
command.COM	O
)	O
and	O
then	O
for	O
executable	O
images	O
(	O
command.EXE	O
)	O
with	O
filenames	O
that	O
match	O
the	O
command	O
that	O
was	O
input	O
by	O
the	O
user	O
.	O
</s>
<s>
Like	O
traditional	O
foreign	O
commands	B-Application
,	O
automatic	O
foreign	O
commands	B-Application
also	O
allow	O
Unix-style	O
command	O
input	O
.	O
</s>
<s>
DCL	O
scripts	O
look	O
much	O
like	O
any	O
other	O
scripting	B-Language
language	I-Language
,	O
with	O
some	O
exceptions	O
.	O
</s>
<s>
For	O
example	O
,	O
to	O
use	O
the	O
TYPE	B-Device
command	O
to	O
print	B-Device
a	O
paragraph	O
onto	O
the	O
screen	O
,	O
one	O
might	O
use	O
a	O
script	O
similar	O
to	O
:	O
</s>
<s>
The	O
following	O
is	O
a	O
list	O
of	O
DCL	O
commands	B-Application
for	O
common	O
computing	O
tasks	O
that	O
are	O
supported	O
by	O
the	O
OpenVMS	B-Operating_System
command-line	B-Application
interface	I-Application
.	O
</s>
<s>
Lexical	O
functions	O
provide	O
string	O
functions	O
and	O
access	O
to	O
VMS-maintained	O
data	O
.	O
</s>
