<s>
A	O
command-line	B-Application
interpreter	B-Application
or	O
command-line	B-Application
processor	O
uses	O
a	O
command-line	B-Application
interface	I-Application
(	O
CLI	O
)	O
to	O
receive	O
commands	O
from	O
a	O
user	O
in	O
the	O
form	O
of	O
lines	O
of	O
text	O
.	O
</s>
<s>
This	O
provides	O
a	O
means	O
of	O
setting	O
parameters	O
for	O
the	O
environment	O
,	O
invoking	O
executables	B-Application
and	O
providing	O
information	O
to	O
them	O
as	O
to	O
what	O
actions	O
they	O
are	O
to	O
perform	O
.	O
</s>
<s>
In	O
some	O
cases	O
the	O
invocation	O
is	O
conditional	O
based	O
on	O
conditions	O
established	O
by	O
the	O
user	O
or	O
previous	O
executables	B-Application
.	O
</s>
<s>
Such	O
access	O
was	O
first	O
provided	O
by	O
computer	B-General_Concept
terminals	I-General_Concept
starting	O
in	O
the	O
mid-1960s	O
.	O
</s>
<s>
This	O
provided	O
an	O
interactive	O
environment	O
not	O
available	O
with	O
punched	B-Architecture
cards	I-Architecture
or	O
other	O
input	O
methods	O
.	O
</s>
<s>
Today	O
,	O
many	O
users	O
rely	O
upon	O
graphical	B-Application
user	I-Application
interfaces	I-Application
and	O
menu-driven	O
interactions	O
.	O
</s>
<s>
However	O
,	O
some	O
programming	O
and	O
maintenance	O
tasks	O
may	O
not	O
have	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
and	O
use	O
a	O
command	B-Application
line	I-Application
.	O
</s>
<s>
Alternatives	O
to	O
the	O
command-line	B-Application
interface	I-Application
include	O
text-based	B-Application
user	I-Application
interface	I-Application
menus	O
(	O
for	O
example	O
,	O
IBM	B-Device
AIX	I-Device
SMIT	I-Device
)	O
,	O
keyboard	O
shortcuts	O
,	O
and	O
various	O
desktop	B-Application
metaphors	I-Application
centered	O
on	O
the	O
pointer	O
(	O
usually	O
controlled	O
with	O
a	O
mouse	B-Device
)	O
.	O
</s>
<s>
Examples	O
of	O
this	O
include	O
the	O
Microsoft	B-Application
Windows	I-Application
,	O
DOS	B-Application
Shell	I-Application
,	O
and	O
Mouse	B-Device
Systems	O
PowerPanel	O
.	O
</s>
<s>
Command-line	B-Application
interfaces	I-Application
are	O
often	O
implemented	O
in	O
terminal	B-Application
devices	O
that	O
are	O
also	O
capable	O
of	O
screen-oriented	O
text-based	B-Application
user	I-Application
interfaces	I-Application
that	O
use	O
cursor	O
addressing	O
to	O
place	O
symbols	O
on	O
a	O
display	O
screen	O
.	O
</s>
<s>
Programs	O
with	O
command-line	B-Application
interfaces	I-Application
are	O
generally	O
easier	O
to	O
automate	O
via	O
scripting	B-Language
.	O
</s>
<s>
Many	O
software	O
systems	O
implement	O
command-line	B-Application
interfaces	I-Application
for	O
control	O
and	O
operation	O
.	O
</s>
<s>
Compared	O
with	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
a	O
command-line	B-Application
interface	I-Application
requires	O
fewer	O
system	O
resources	O
to	O
implement	O
.	O
</s>
<s>
Since	O
options	O
to	O
commands	O
are	O
given	O
in	O
a	O
few	O
characters	O
in	O
each	O
command	B-Application
line	I-Application
,	O
an	O
experienced	O
user	O
often	O
finds	O
the	O
options	O
easier	O
to	O
access	O
.	O
</s>
<s>
Automation	O
of	O
repetitive	O
tasks	O
is	O
simplified	O
by	O
line	O
editing	O
and	O
history	O
mechanisms	O
for	O
storing	O
frequently	O
used	O
sequences	O
;	O
this	O
may	O
extend	O
to	O
a	O
scripting	B-Language
language	I-Language
that	O
can	O
take	O
parameters	O
and	O
variable	O
options	O
.	O
</s>
<s>
A	O
command-line	B-Application
history	O
can	O
be	O
kept	O
,	O
allowing	O
review	O
or	O
repetition	O
of	O
commands	O
.	O
</s>
<s>
A	O
command-line	B-Application
system	O
may	O
require	O
paper	O
or	O
online	O
manuals	O
for	O
the	O
user	O
's	O
reference	O
,	O
although	O
often	O
a	O
"	O
help	B-Protocol
"	O
option	O
provides	O
a	O
concise	O
review	O
of	O
the	O
options	O
of	O
a	O
command	B-Application
.	O
</s>
<s>
The	O
command-line	B-Application
environment	O
may	O
not	O
provide	O
graphical	O
enhancements	O
such	O
as	O
different	O
fonts	O
or	O
extended	O
edit	O
windows	O
found	O
in	O
a	O
GUI	B-Application
.	O
</s>
<s>
It	O
may	O
be	O
difficult	O
for	O
a	O
new	O
user	O
to	O
become	O
familiar	O
with	O
all	O
the	O
commands	O
and	O
options	O
available	O
,	O
compared	O
with	O
the	O
icons	O
and	O
drop-down	O
menus	O
of	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
without	O
reference	O
to	O
manuals	O
.	O
</s>
<s>
Operating	B-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
command-line	B-Application
interfaces	I-Application
are	O
usually	O
distinct	O
programs	O
supplied	O
with	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
A	O
program	O
that	O
implements	O
such	O
a	O
text	O
interface	O
is	O
often	O
called	O
a	O
command-line	B-Application
interpreter	B-Application
,	O
command	B-Application
processor	O
or	O
shell	B-Application
.	O
</s>
<s>
Examples	O
of	O
command-line	B-Application
interpreters	B-Application
include	O
DEC	O
's	O
DIGITAL	B-Operating_System
Command	I-Operating_System
Language	I-Operating_System
(	O
DCL	B-Operating_System
)	O
in	O
OpenVMS	B-Operating_System
and	O
RSX-11	B-Application
,	O
the	O
various	O
Unix	B-Application
shells	I-Application
(	O
sh	B-Device
,	O
ksh	B-Language
,	O
csh	B-Operating_System
,	O
tcsh	B-Language
,	O
zsh	B-Application
,	O
Bash	B-Operating_System
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
CP/M	B-Application
'	O
s	O
CCP	O
,	O
DOS	B-Device
 '	O
COMMAND.COM	B-Operating_System
,	O
as	O
well	O
as	O
the	O
OS/2	B-Application
and	O
the	O
Windows	O
CMD.EXE	B-Device
programs	O
,	O
the	O
latter	O
groups	O
being	O
based	O
heavily	O
on	O
DEC	O
's	O
RSX-11	B-Application
and	O
RSTS	B-Operating_System
CLIs	O
.	O
</s>
<s>
Under	O
most	O
operating	B-General_Concept
systems	I-General_Concept
,	O
it	O
is	O
possible	O
to	O
replace	O
the	O
default	B-General_Concept
shell	B-Application
program	O
with	O
alternatives	O
;	O
examples	O
include	O
4DOS	B-Application
for	O
DOS	B-Device
,	O
4OS2	B-Application
for	O
OS/2	B-Application
,	O
and	O
4NT	B-Application
/	I-Application
Take	I-Application
Command	I-Application
for	O
Windows	O
.	O
</s>
<s>
Although	O
the	O
term	O
'	O
shell	B-Application
 '	O
is	O
often	O
used	O
to	O
describe	O
a	O
command-line	B-Application
interpreter	B-Application
,	O
strictly	O
speaking	O
,	O
a	O
'	O
shell	B-Application
 '	O
can	O
be	O
any	O
program	O
that	O
constitutes	O
the	O
user-interface	O
,	O
including	O
fully	O
graphically	O
oriented	O
ones	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
default	B-General_Concept
Windows	O
GUI	B-Application
is	O
a	O
shell	B-Application
program	O
named	O
EXPLORER.EXE	B-Protocol
,	O
as	O
defined	O
in	O
the	O
SHELL	B-Application
=	O
EXPLORER.EXE	B-Protocol
line	O
in	O
the	O
WIN.INI	O
configuration	O
file	B-Operating_System
.	O
</s>
<s>
Application	B-Application
programs	I-Application
(	O
as	O
opposed	O
to	O
operating	B-General_Concept
systems	I-General_Concept
)	O
may	O
also	O
have	O
command-line	B-Application
interfaces	I-Application
.	O
</s>
<s>
An	O
application	B-Application
program	I-Application
may	O
support	O
none	O
,	O
any	O
,	O
or	O
all	O
of	O
these	O
three	O
major	O
types	O
of	O
command-line	B-Application
interface	I-Application
mechanisms	O
:	O
</s>
<s>
Parameters	O
:	O
Most	O
command-line	B-Application
interfaces	I-Application
support	O
a	O
means	O
to	O
pass	O
additional	O
information	O
to	O
a	O
program	O
when	O
it	O
is	O
launched	O
.	O
</s>
<s>
Interactive	O
command-line	B-Application
sessions	O
:	O
After	O
launch	O
,	O
a	O
program	O
may	O
provide	O
an	O
operator	O
with	O
an	O
independent	O
means	O
to	O
enter	O
commands	O
.	O
</s>
<s>
Inter-process	B-Operating_System
communication	I-Operating_System
:	O
Most	O
operating	B-General_Concept
systems	I-General_Concept
support	O
means	O
of	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
for	O
example	O
,	O
standard	B-Operating_System
streams	I-Operating_System
or	O
named	B-Operating_System
pipes	I-Operating_System
)	O
.	O
</s>
<s>
Command	B-Application
lines	I-Application
from	O
client	O
processes	O
may	O
be	O
redirected	O
to	O
a	O
CLI	O
program	O
by	O
one	O
of	O
these	O
methods	O
.	O
</s>
<s>
Some	O
applications	O
support	O
a	O
CLI	O
,	O
presenting	O
their	O
own	O
prompt	O
to	O
the	O
user	O
and	O
accepting	O
command	B-Application
lines	I-Application
.	O
</s>
<s>
Other	O
programs	O
support	O
both	O
a	O
CLI	O
and	O
a	O
GUI	B-Application
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
a	O
GUI	B-Application
is	O
simply	O
a	O
wrapper	O
around	O
a	O
separate	O
CLI	O
executable	B-Application
file	I-Application
.	O
</s>
<s>
In	O
other	O
cases	O
,	O
a	O
program	O
may	O
provide	O
a	O
CLI	O
as	O
an	O
optional	O
alternative	O
to	O
its	O
GUI	B-Application
.	O
</s>
<s>
CLIs	O
and	O
GUIs	B-Application
often	O
support	O
different	O
functionality	O
.	O
</s>
<s>
For	O
example	O
,	O
all	O
features	O
of	O
MATLAB	B-Language
,	O
a	O
numerical	B-General_Concept
analysis	I-General_Concept
computer	B-Application
program	I-Application
,	O
are	O
available	O
via	O
the	O
CLI	O
,	O
whereas	O
the	O
MATLAB	B-Language
GUI	B-Application
exposes	O
only	O
a	O
subset	O
of	O
features	O
.	O
</s>
<s>
In	O
Colossal	B-Application
Cave	I-Application
Adventure	I-Application
from	O
1975	O
,	O
the	O
user	O
uses	O
a	O
CLI	O
to	O
enter	O
one	O
or	O
two	O
words	O
to	O
explore	O
a	O
cave	O
system	O
.	O
</s>
<s>
The	O
command-line	B-Application
interface	I-Application
evolved	O
from	O
a	O
form	O
of	O
communication	O
conducted	O
by	O
people	O
over	O
teleprinter	O
(	O
TTY	O
)	O
machines	O
.	O
</s>
<s>
Sometimes	O
these	O
involved	O
sending	O
an	O
order	O
or	O
a	O
confirmation	O
using	O
telex	B-Application
.	O
</s>
<s>
The	O
mechanical	O
teleprinter	O
was	O
replaced	O
by	O
a	O
"	O
glass	B-General_Concept
tty	I-General_Concept
"	O
,	O
a	O
keyboard	O
and	O
screen	O
emulating	O
the	O
teleprinter	O
.	O
</s>
<s>
"	O
Smart	O
"	O
terminals	O
permitted	O
additional	O
functions	O
,	O
such	O
as	O
cursor	O
movement	O
over	O
the	O
entire	O
screen	O
,	O
or	O
local	O
editing	O
of	O
data	O
on	O
the	O
terminal	B-Application
for	O
transmission	O
to	O
the	O
computer	O
.	O
</s>
<s>
As	O
the	O
microcomputer	O
revolution	O
replaced	O
the	O
traditionalminicomputer	O
+	O
terminalstime	O
sharing	O
architecture	O
,	O
hardware	O
terminals	O
were	O
replaced	O
by	O
terminal	B-Application
emulators	I-Application
—	O
PC	O
software	O
that	O
interpreted	O
terminal	B-Application
signals	O
sent	O
through	O
the	O
PC	O
's	O
serial	B-Protocol
ports	I-Protocol
.	O
</s>
<s>
Some	O
of	O
these	O
PCs	O
were	O
running	O
Bulletin	B-Application
Board	I-Application
System	I-Application
software	O
.	O
</s>
<s>
Early	O
operating	B-General_Concept
system	I-General_Concept
CLIs	O
were	O
implemented	O
as	O
part	O
of	O
resident	B-Application
monitor	I-Application
programs	O
,	O
and	O
could	O
not	O
easily	O
be	O
replaced	O
.	O
</s>
<s>
The	O
first	O
implementation	O
of	O
the	O
shell	B-Application
as	O
a	O
replaceable	O
component	O
was	O
part	O
of	O
the	O
Multics	B-Application
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
.	O
</s>
<s>
In	O
1964	O
,	O
MIT	O
Computation	O
Center	O
staff	O
member	O
Louis	O
Pouzin	O
developed	O
the	O
RUNCOM	B-Device
tool	O
for	O
executing	O
command	B-Application
scripts	O
while	O
allowing	O
argument	O
substitution	O
.	O
</s>
<s>
Pouzin	O
coined	O
the	O
term	O
"	O
shell	B-Application
"	O
to	O
describe	O
the	O
technique	O
of	O
using	O
commands	O
like	O
a	O
programming	O
language	O
,	O
and	O
wrote	O
a	O
paper	O
about	O
how	O
to	O
implement	O
the	O
idea	O
in	O
the	O
Multics	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
Pouzin	O
returned	O
to	O
his	O
native	O
France	O
in	O
1965	O
,	O
and	O
the	O
first	O
Multics	B-Application
shell	B-Application
was	O
developed	O
by	O
Glenda	O
Schroeder	O
.	O
</s>
<s>
The	O
first	O
Unix	B-Application
shell	I-Application
,	O
the	O
V6	B-Application
shell	I-Application
,	O
was	O
developed	O
by	O
Ken	O
Thompson	O
in	O
1971	O
at	O
Bell	O
Labs	O
and	O
was	O
modeled	O
after	O
Schroeder	O
's	O
Multics	B-Application
shell	B-Application
.	O
</s>
<s>
The	B-Device
Bourne	I-Device
shell	I-Device
was	O
introduced	O
in	O
1977	O
as	O
a	O
replacement	O
for	O
the	O
V6	B-Application
shell	I-Application
.	O
</s>
<s>
Although	O
it	O
is	O
used	O
as	O
an	O
interactive	O
command	B-Application
interpreter	B-Application
,	O
it	O
was	O
also	O
intended	O
as	O
a	O
scripting	B-Language
language	I-Language
and	O
contains	O
most	O
of	O
the	O
features	O
that	O
are	O
commonly	O
considered	O
to	O
produce	O
structured	O
programs	O
.	O
</s>
<s>
The	B-Device
Bourne	I-Device
shell	I-Device
led	O
to	O
the	O
development	O
of	O
the	O
KornShell	B-Language
(	O
ksh	B-Language
)	O
,	O
Almquist	B-Operating_System
shell	I-Operating_System
(	O
ash	B-Operating_System
)	O
,	O
and	O
the	O
popular	O
Bourne-again	B-Operating_System
shell	I-Operating_System
(	O
or	O
Bash	B-Operating_System
)	O
.	O
</s>
<s>
Early	O
microcomputers	O
themselves	O
were	O
based	O
on	O
a	O
command-line	B-Application
interface	I-Application
such	O
as	O
CP/M	B-Application
,	O
DOS	B-Device
or	O
AppleSoft	B-Language
BASIC	I-Language
.	O
</s>
<s>
During	O
the	O
1980s	O
and	O
1990s	O
,	O
the	O
introduction	O
of	O
the	O
Apple	B-Device
Macintosh	I-Device
and	O
of	O
Microsoft	B-Application
Windows	I-Application
on	O
PCs	O
saw	O
the	O
command	B-Application
line	I-Application
interface	I-Application
as	O
the	O
primary	O
user	O
interface	O
replaced	O
by	O
the	O
Graphical	B-Application
User	I-Application
Interface	I-Application
.	O
</s>
<s>
The	O
command	B-Application
line	I-Application
remained	O
available	O
as	O
an	O
alternative	O
user	O
interface	O
,	O
often	O
used	O
by	O
system	B-Application
administrators	I-Application
and	O
other	O
advanced	O
users	O
for	O
system	B-Application
administration	I-Application
,	O
computer	B-General_Concept
programming	I-General_Concept
and	O
batch	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
In	O
November	O
2006	O
,	O
Microsoft	O
released	O
version	O
1.0	O
of	O
Windows	B-Application
PowerShell	I-Application
(	O
formerly	O
codenamed	O
Monad	O
)	O
,	O
which	O
combined	O
features	O
of	O
traditional	B-Application
Unix	I-Application
shells	O
with	O
their	O
proprietary	O
object-oriented	O
.NET	B-Application
Framework	I-Application
.	O
</s>
<s>
MinGW	B-Application
and	O
Cygwin	B-Language
are	O
open-source	B-Application
packages	O
for	O
Windows	O
that	O
offer	O
a	O
Unix-like	B-Operating_System
CLI	O
.	O
</s>
<s>
Microsoft	O
provides	O
MKS	O
Inc.	O
'	O
s	O
ksh	B-Language
implementation	O
MKS	O
Korn	B-Language
shell	I-Language
for	O
Windows	O
through	O
their	O
Services	O
for	O
UNIX	B-Application
add-on	O
.	O
</s>
<s>
Since	O
2001	O
,	O
the	O
Macintosh	B-Device
operating	B-General_Concept
system	I-General_Concept
macOS	B-Application
has	O
been	O
based	O
on	O
a	O
Unix-like	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
called	O
Darwin	B-Operating_System
.	O
</s>
<s>
On	O
these	O
computers	O
,	O
users	O
can	O
access	O
a	O
Unix-like	B-Operating_System
command-line	B-Application
interface	I-Application
by	O
running	O
the	O
terminal	B-Application
emulator	I-Application
program	O
called	O
Terminal	B-Application
,	O
which	O
is	O
found	O
in	O
the	O
Utilities	O
sub-folder	O
of	O
the	O
Applications	O
folder	O
,	O
or	O
by	O
remotely	O
logging	O
into	O
the	O
machine	O
using	O
ssh	B-Protocol
.	O
</s>
<s>
Z	B-Application
shell	I-Application
is	O
the	O
default	B-General_Concept
shell	B-Application
for	O
macOS	B-Application
;	O
Bash	B-Operating_System
,	O
tcsh	B-Language
,	O
and	O
the	O
KornShell	B-Language
are	O
also	O
provided	O
.	O
</s>
<s>
Before	O
macOS	B-Device
Catalina	I-Device
,	O
Bash	B-Operating_System
was	O
the	O
default	B-General_Concept
.	O
</s>
<s>
A	O
CLI	O
is	O
used	O
whenever	O
a	O
large	O
vocabulary	O
of	O
commands	O
or	O
queries	O
,	O
coupled	O
with	O
a	O
wide	O
(	O
or	O
arbitrary	O
)	O
range	O
of	O
options	O
,	O
can	O
be	O
entered	O
more	O
rapidly	O
as	O
text	O
than	O
with	O
a	O
pure	O
GUI	B-Application
.	O
</s>
<s>
This	O
is	O
typically	O
the	O
case	O
with	O
operating	B-General_Concept
system	I-General_Concept
command	B-Operating_System
shells	I-Operating_System
.	O
</s>
<s>
CLIs	O
are	O
also	O
used	O
by	O
systems	O
with	O
insufficient	O
resources	O
to	O
support	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
Some	O
computer	O
language	O
systems	O
(	O
such	O
as	O
Python	B-Language
,	O
Forth	B-Application
,	O
LISP	B-Language
,	O
Rexx	B-Language
,	O
and	O
many	O
dialects	O
of	O
BASIC	O
)	O
provide	O
an	O
interactive	O
command-line	B-Application
mode	B-General_Concept
to	O
allow	O
for	O
rapid	O
evaluation	O
of	O
code	O
.	O
</s>
<s>
CLIs	O
are	O
often	O
used	O
by	O
programmers	O
and	O
system	B-Application
administrators	I-Application
,	O
in	O
engineering	O
and	O
scientific	O
environments	O
,	O
and	O
by	O
technically	O
advanced	O
personal	O
computer	O
users	O
.	O
</s>
<s>
The	O
general	O
pattern	O
of	O
a	O
command	B-Application
line	I-Application
interface	I-Application
is	O
:	O
</s>
<s>
Command	B-Application
—	O
provided	O
by	O
the	O
user	O
.	O
</s>
<s>
Internal	O
commands	O
are	O
recognized	O
and	O
processed	O
by	O
the	O
command	B-Application
line	I-Application
interpreter	B-Application
.	O
</s>
<s>
Included	O
commands	O
run	O
separate	O
executables	B-Application
.	O
</s>
<s>
External	O
commands	O
run	O
executable	B-Application
files	I-Application
that	O
may	O
be	O
included	O
by	O
other	O
parties	O
.	O
</s>
<s>
The	O
format	O
and	O
meaning	O
of	O
the	O
parameters	O
depends	O
upon	O
the	O
command	B-Application
.	O
</s>
<s>
In	O
this	O
format	O
,	O
the	O
delimiters	B-Algorithm
between	O
command-line	B-Application
elements	O
are	O
whitespace	O
characters	O
and	O
the	O
end-of-line	O
delimiter	B-Algorithm
is	O
the	O
newline	O
delimiter	B-Algorithm
.	O
</s>
<s>
A	O
CLI	O
can	O
generally	O
be	O
considered	O
as	O
consisting	O
of	O
syntax	O
and	O
semantics	B-Application
.	O
</s>
<s>
In	O
the	O
case	O
of	O
operating	B-General_Concept
systems	I-General_Concept
,	O
DOS	B-Device
and	O
Unix	B-Application
each	O
define	O
their	O
own	O
set	O
of	O
rules	O
that	O
all	O
commands	O
must	O
follow	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
embedded	B-Architecture
systems	I-Architecture
,	O
each	O
vendor	O
,	O
such	O
as	O
Nortel	O
,	O
Juniper	O
Networks	O
or	O
Cisco	O
Systems	O
,	O
defines	O
their	O
own	O
proprietary	O
set	O
of	O
rules	O
.	O
</s>
<s>
The	O
semantics	B-Application
define	O
what	O
sort	O
of	O
operations	O
are	O
possible	O
,	O
on	O
what	O
sort	O
of	O
data	O
these	O
operations	O
can	O
be	O
performed	O
,	O
and	O
how	O
the	O
grammar	O
represents	O
these	O
operations	O
and	O
data	O
—	O
the	O
symbolic	O
meaning	O
in	O
the	O
syntax	O
.	O
</s>
<s>
Two	O
different	O
CLIs	O
may	O
agree	O
on	O
either	O
syntax	O
or	O
semantics	B-Application
,	O
but	O
it	O
is	O
only	O
when	O
they	O
agree	O
on	O
both	O
that	O
they	O
can	O
be	O
considered	O
sufficiently	O
similar	O
to	O
allow	O
users	O
to	O
use	O
both	O
CLIs	O
without	O
needing	O
to	O
learn	O
anything	O
,	O
as	O
well	O
as	O
to	O
enable	O
re-use	O
of	O
scripts	O
.	O
</s>
<s>
A	O
simple	O
CLI	O
will	O
display	O
a	O
prompt	O
,	O
accept	O
a	O
"	O
command	B-Application
line	I-Application
"	O
typed	O
by	O
the	O
user	O
terminated	O
by	O
the	O
Enter	B-Device
key	I-Device
,	O
then	O
execute	O
the	O
specified	O
command	B-Application
and	O
provide	O
textual	O
display	O
of	O
results	O
or	O
error	O
messages	O
.	O
</s>
<s>
Advanced	O
CLIs	O
will	O
validate	O
,	O
interpret	B-Application
and	O
parameter-expand	O
the	O
command	B-Application
line	I-Application
before	O
executing	O
the	O
specified	O
command	B-Application
,	O
and	O
optionally	O
capture	O
or	O
redirect	O
its	O
output	O
.	O
</s>
<s>
Unlike	O
a	O
button	O
or	O
menu	O
item	O
in	O
a	O
GUI	B-Application
,	O
a	O
command	B-Application
line	I-Application
is	O
typically	O
self-documenting	O
,	O
stating	O
exactly	O
what	O
the	O
user	O
wants	O
done	O
.	O
</s>
<s>
In	O
addition	O
,	O
command	B-Application
lines	I-Application
usually	O
include	O
many	O
defaults	O
that	O
can	O
be	O
changed	O
to	O
customize	O
the	O
results	O
.	O
</s>
<s>
Useful	O
command	B-Application
lines	I-Application
can	O
be	O
saved	O
by	O
assigning	O
a	O
character	O
string	O
or	O
alias	B-Device
to	O
represent	O
the	O
full	O
command	B-Application
,	O
or	O
several	O
commands	O
can	O
be	O
grouped	O
to	O
perform	O
a	O
more	O
complex	O
sequence	O
–	O
for	O
instance	O
,	O
compile	O
the	O
program	O
,	O
install	O
it	O
,	O
and	O
run	O
it	O
—	O
creating	O
a	O
single	O
entity	O
,	O
called	O
a	O
command	B-Application
procedure	O
or	O
script	O
which	O
itself	O
can	O
be	O
treated	O
as	O
a	O
command	B-Application
.	O
</s>
<s>
These	O
advantages	O
mean	O
that	O
a	O
user	O
must	O
figure	O
out	O
a	O
complex	O
command	B-Application
or	O
series	O
of	O
commands	O
only	O
once	O
,	O
because	O
they	O
can	O
be	O
saved	O
,	O
to	O
be	O
used	O
again	O
.	O
</s>
<s>
The	O
commands	O
given	O
to	O
a	O
CLI	O
shell	B-Application
are	O
often	O
in	O
one	O
of	O
the	O
following	O
forms	O
:	O
</s>
<s>
where	O
doSomething	O
is	O
,	O
in	O
effect	O
,	O
a	O
verb	O
,	O
how	O
an	O
adverb	O
(	O
for	O
example	O
,	O
should	O
the	O
command	B-Application
be	O
executed	O
"	O
verbosely	O
"	O
or	O
"	O
quietly	O
"	O
)	O
and	O
toFiles	O
an	O
object	O
or	O
objects	O
(	O
typically	O
one	O
or	O
more	O
files	O
)	O
on	O
which	O
the	O
command	B-Application
should	O
act	O
.	O
</s>
<s>
The	O
>	O
in	O
the	O
third	O
example	O
is	O
a	O
redirection	B-Device
operator	I-Device
,	O
telling	O
the	O
command-line	B-Application
interpreter	B-Application
to	O
send	O
the	O
output	O
of	O
the	O
command	B-Application
not	O
to	O
its	O
own	O
standard	O
output	O
(	O
the	O
screen	O
)	O
but	O
to	O
the	O
named	O
file	B-Operating_System
.	O
</s>
<s>
This	O
will	O
overwrite	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Using	O
>>	O
will	O
redirect	O
the	O
output	O
and	O
append	O
it	O
to	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Another	O
redirection	B-Device
operator	I-Device
is	O
the	O
vertical	O
bar	O
( |	O
)	O
,	O
which	O
creates	O
a	O
pipeline	B-Operating_System
where	O
the	O
output	O
of	O
one	O
command	B-Application
becomes	O
the	O
input	O
to	O
the	O
next	O
command	B-Application
.	O
</s>
<s>
One	O
can	O
modify	O
the	O
set	O
of	O
available	O
commands	O
by	O
modifying	O
which	O
paths	O
appear	O
in	O
the	O
PATH	B-Application
environment	O
variable	O
.	O
</s>
<s>
Under	O
Unix	B-Application
,	O
commands	O
also	O
need	O
be	O
marked	O
as	O
executable	B-Application
files	I-Application
.	O
</s>
<s>
The	O
directories	O
in	O
the	O
path	B-Application
variable	I-Application
are	O
searched	O
in	O
the	O
order	O
they	O
are	O
given	O
.	O
</s>
<s>
By	O
re-ordering	O
the	O
path	B-Application
,	O
one	O
can	O
run	O
e.g.	O
</s>
<s>
\OS2\MDOS\E.EXE	O
instead	O
of	O
\OS2\E.EXE,	O
when	O
the	O
default	B-General_Concept
is	O
the	O
opposite	O
.	O
</s>
<s>
Renaming	O
of	O
the	O
executables	B-Application
also	O
works	O
:	O
people	O
often	O
rename	O
their	O
favourite	O
editor	O
to	O
EDIT	O
,	O
for	O
example	O
.	O
</s>
<s>
The	O
command	B-Application
line	I-Application
allows	O
one	O
to	O
restrict	O
available	O
commands	O
,	O
such	O
as	O
access	O
to	O
advanced	O
internal	O
commands	O
.	O
</s>
<s>
The	O
Windows	O
CMD.EXE	B-Device
does	O
this	O
.	O
</s>
<s>
Often	O
,	O
shareware	O
programs	O
will	O
limit	O
the	O
range	O
of	O
commands	O
,	O
including	O
printing	O
a	O
command	B-Application
'	O
your	O
administrator	O
has	O
disabled	O
running	O
batch	B-General_Concept
files	O
 '	O
from	O
the	O
prompt	O
.	O
</s>
<s>
Some	O
CLIs	O
,	O
such	O
as	O
those	O
in	O
network	B-Protocol
routers	I-Protocol
,	O
have	O
a	O
hierarchy	O
of	O
modes	O
,	O
with	O
a	O
different	O
set	O
of	O
commands	O
supported	O
in	O
each	O
mode	B-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
CLI	O
had	O
two	O
modes	O
called	O
interface	O
and	O
system	O
,	O
the	O
user	O
might	O
use	O
the	O
command	B-Application
interface	O
to	O
enter	O
the	O
interface	O
mode	B-General_Concept
.	O
</s>
<s>
At	O
this	O
point	O
,	O
commands	O
from	O
the	O
system	O
mode	B-General_Concept
may	O
not	O
be	O
accessible	O
until	O
the	O
user	O
exits	O
the	O
interface	O
mode	B-General_Concept
and	O
enters	O
the	O
system	O
mode	B-General_Concept
.	O
</s>
<s>
A	O
command	B-Device
prompt	I-Device
(	O
or	O
just	O
prompt	O
)	O
is	O
a	O
sequence	O
of	O
(	O
one	O
or	O
more	O
)	O
characters	O
used	O
in	O
a	O
command-line	B-Application
interface	I-Application
to	O
indicate	O
readiness	O
to	O
accept	O
commands	O
.	O
</s>
<s>
A	O
prompt	O
usually	O
ends	O
with	O
one	O
of	O
the	O
characters	O
$	O
,	O
%	O
,	O
#	O
,	O
:	O
,	O
>	O
or	O
-	O
and	O
often	O
includes	O
other	O
information	O
,	O
such	O
as	O
the	O
path	B-Application
of	O
the	O
current	B-Application
working	I-Application
directory	I-Application
and	O
the	O
hostname	B-Protocol
.	O
</s>
<s>
On	O
many	O
Unix	B-Application
and	O
derivative	B-Operating_System
systems	I-Operating_System
,	O
the	O
prompt	O
commonly	O
ends	O
in	O
$	O
or	O
%	O
if	O
the	O
user	O
is	O
a	O
normal	O
user	O
,	O
but	O
in	O
#	O
if	O
the	O
user	O
is	O
a	O
superuser	B-Application
(	O
"	O
root	O
"	O
in	O
Unix	B-Application
terminology	O
)	O
.	O
</s>
<s>
Depending	O
on	O
the	O
environment	O
,	O
they	O
may	O
include	O
colors	O
,	O
special	O
characters	O
,	O
and	O
other	O
elements	O
(	O
like	O
variables	O
and	O
functions	O
for	O
the	O
current	O
time	O
,	O
user	O
,	O
shell	B-Application
number	O
or	O
working	B-Application
directory	I-Application
)	O
in	O
order	O
,	O
for	O
instance	O
,	O
to	O
make	O
the	O
prompt	O
more	O
informative	O
or	O
visually	O
pleasing	O
,	O
to	O
distinguish	O
sessions	O
on	O
various	O
machines	O
,	O
or	O
to	O
indicate	O
the	O
current	O
level	O
of	O
nesting	O
of	O
commands	O
.	O
</s>
<s>
On	O
some	O
systems	O
,	O
special	O
tokens	O
in	O
the	O
definition	O
of	O
the	O
prompt	O
can	O
be	O
used	O
to	O
cause	O
external	O
programs	O
to	O
be	O
called	O
by	O
the	O
command-line	B-Application
interpreter	B-Application
while	O
displaying	O
the	O
prompt	O
.	O
</s>
<s>
In	O
DOS	B-Device
 '	O
COMMAND.COM	B-Operating_System
and	O
in	O
Windows	B-Device
NT	I-Device
's	O
cmd.exe	B-Device
users	O
can	O
modify	O
the	O
prompt	O
by	O
issuing	O
a	O
PROMPT	O
command	B-Application
or	O
by	O
directly	O
changing	O
the	O
value	O
of	O
the	O
corresponding	O
%PROMPT%	O
environment	O
variable	O
.	O
</s>
<s>
The	O
default	B-General_Concept
of	O
most	O
modern	O
systems	O
,	O
the	O
C:\>	O
style	O
is	O
obtained	O
,	O
for	O
instance	O
,	O
with	O
PROMPT	O
$P$G	O
.	O
</s>
<s>
The	O
default	B-General_Concept
of	O
older	O
DOS	B-Device
systems	O
,	O
C>	O
is	O
obtained	O
by	O
just	O
PROMPT	O
,	O
although	O
on	O
some	O
systems	O
this	O
produces	O
the	O
newer	O
C:\>	O
style	O
,	O
unless	O
used	O
on	O
floppy	O
drives	O
A	O
:	O
or	O
B	O
:	O
;	O
on	O
those	O
systems	O
PROMPT	O
$N$G	O
can	O
be	O
used	O
to	O
override	O
the	O
automatic	O
default	B-General_Concept
and	O
explicitly	O
switch	O
to	O
the	O
older	O
style	O
.	O
</s>
<s>
Many	O
Unix	B-Application
systems	I-Application
feature	O
the	O
$PS1	O
variable	O
(	O
Prompt	O
String	O
1	O
)	O
,	O
although	O
other	O
variables	O
also	O
may	O
affect	O
the	O
prompt	O
(	O
depending	O
on	O
the	O
shell	B-Application
used	O
)	O
.	O
</s>
<s>
In	O
the	O
Bash	B-Operating_System
shell	I-Operating_System
,	O
a	O
prompt	O
of	O
the	O
form	O
:	O
</s>
<s>
In	O
zsh	B-Application
the	O
$RPROMPT	O
variable	O
controls	O
an	O
optional	O
"	O
prompt	O
"	O
on	O
the	O
right-hand	O
side	O
of	O
the	O
display	O
.	O
</s>
<s>
In	O
RISC	B-Operating_System
OS	I-Operating_System
the	O
command	B-Device
prompt	I-Device
is	O
a	O
*	O
symbol	O
,	O
and	O
thus	O
(	O
OS	O
)	O
CLI	O
commands	O
are	O
often	O
referred	O
to	O
as	O
"	O
star	O
commands	O
"	O
.	O
</s>
<s>
One	O
can	O
also	O
access	O
the	O
same	O
commands	O
from	O
other	O
command	B-Application
lines	I-Application
(	O
such	O
as	O
the	O
BBC	B-Language
BASIC	I-Language
command	B-Application
line	I-Application
)	O
,	O
by	O
preceding	O
the	O
command	B-Application
with	O
a	O
*	O
.	O
</s>
<s>
A	O
command-line	B-Application
argument	O
or	O
parameter	O
is	O
an	O
item	O
of	O
information	O
provided	O
to	O
a	O
program	O
when	O
it	O
is	O
started	O
.	O
</s>
<s>
A	O
program	O
can	O
have	O
many	O
command-line	B-Application
arguments	O
that	O
identify	O
sources	O
or	O
destinations	O
of	O
information	O
,	O
or	O
that	O
alter	O
the	O
operation	O
of	O
the	O
program	O
.	O
</s>
<s>
When	O
a	O
command	B-Application
processor	O
is	O
active	O
a	O
program	O
is	O
typically	O
invoked	O
by	O
typing	O
its	O
name	O
followed	O
by	O
command-line	B-Application
arguments	O
(	O
if	O
any	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
environments	O
,	O
an	O
example	O
of	O
a	O
command-line	B-Application
argument	O
is	O
:	O
</s>
<s>
"	O
file.s	O
"	O
is	O
a	O
command-line	B-Application
argument	O
which	O
tells	O
the	O
program	O
rm	B-Application
to	O
remove	O
the	O
file	B-Operating_System
"	O
file.s	O
"	O
.	O
</s>
<s>
Some	O
programming	O
languages	O
,	O
such	O
as	O
C	B-Language
,	O
C++	B-Language
and	O
Java	B-Language
,	O
allow	O
a	O
program	O
to	O
interpret	B-Application
the	O
command-line	B-Application
arguments	O
by	O
handling	O
them	O
as	O
string	O
parameters	O
in	O
the	O
main	B-Language
function	I-Language
.	O
</s>
<s>
Other	O
languages	O
,	O
such	O
as	O
Python	B-Language
,	O
expose	O
operating	B-General_Concept
system	I-General_Concept
specific	O
API	B-Application
(	O
functionality	O
)	O
through	O
sys	O
module	B-Architecture
,	O
and	O
in	O
particular	O
sys.argv	O
for	O
"	O
command-line	B-Application
arguments	O
"	O
.	O
</s>
<s>
In	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
a	O
single	O
hyphen	O
used	O
in	O
place	O
of	O
a	O
file	B-Operating_System
name	O
is	O
a	O
special	O
value	O
specifying	O
that	O
a	O
program	O
should	O
handle	O
data	O
coming	O
from	O
the	O
standard	O
input	O
or	O
send	O
data	O
to	O
the	O
standard	O
output	O
.	O
</s>
<s>
A	O
command-line	B-Application
option	O
or	O
simply	O
option	O
(	O
also	O
known	O
as	O
a	O
flag	O
or	O
switch	O
)	O
modifies	O
the	O
operation	O
of	O
a	O
command	B-Application
;	O
the	O
effect	O
is	O
determined	O
by	O
the	O
command	B-Application
's	O
program	O
.	O
</s>
<s>
Options	O
follow	O
the	O
command	B-Application
name	O
on	O
the	O
command	B-Application
line	I-Application
,	O
separated	O
by	O
spaces	O
.	O
</s>
<s>
in	O
DOS	B-Device
,	O
which	O
have	O
the	O
same	O
effect	O
of	O
listing	O
the	O
DIR	O
command	B-Application
's	O
available	O
options	O
,	O
whereas	O
dir	O
--help	O
(	O
in	O
many	O
versions	O
of	O
Unix	B-Application
)	O
does	O
require	O
the	O
option	O
to	O
be	O
preceded	O
by	O
at	O
least	O
one	O
space	O
(	O
and	O
is	O
case-sensitive	O
)	O
.	O
</s>
<s>
The	O
format	O
of	O
options	O
varies	O
widely	O
between	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
In	O
most	O
cases	O
the	O
syntax	O
is	O
by	O
convention	O
rather	O
than	O
an	O
operating	B-General_Concept
system	I-General_Concept
requirement	O
;	O
the	O
entire	O
command	B-Application
line	I-Application
is	O
simply	O
a	O
string	O
passed	O
to	O
a	O
program	O
,	O
which	O
can	O
process	O
it	O
in	O
any	O
way	O
the	O
programmer	O
wants	O
,	O
so	O
long	O
as	O
the	O
interpreter	B-Application
can	O
tell	O
where	O
the	O
command	B-Application
name	O
ends	O
and	O
its	O
arguments	O
and	O
options	O
begin	O
.	O
</s>
<s>
A	O
few	O
representative	O
samples	O
of	O
command-line	B-Application
options	O
,	O
all	O
relating	O
to	O
listing	O
files	O
in	O
a	O
directory	O
,	O
to	O
illustrate	O
some	O
conventions	O
:	O
</s>
<s>
Operating	B-General_Concept
system	I-General_Concept
Command	B-Application
Valid	O
alternative	O
Notes	O
OpenVMS	B-Operating_System
directory/owner	O
Dir	O
/Owner	O
instruct	O
the	O
directory	O
command	B-Application
to	O
also	O
display	O
the	O
ownership	O
of	O
the	O
files.Note	O
the	O
Directory	O
command	B-Application
name	O
is	O
not	O
case	O
sensitive	O
,	O
and	O
can	O
be	O
abbreviated	O
to	O
as	O
few	O
letters	O
as	O
required	O
to	O
remain	O
unique	O
.	O
</s>
<s>
Unix-like	B-Operating_System
systems	I-Operating_System
ls	O
-lS	O
D*	O
ls	O
-S	O
-l	O
D*	O
display	O
in	O
long	O
format	O
files	O
and	O
directories	O
beginning	O
with	O
"	O
D	O
"	O
(	O
but	O
not	O
"	O
d	O
"	O
)	O
,	O
sorted	O
by	O
size	O
(	O
largest	O
first	O
)	O
.Note	O
spaces	O
are	O
required	O
around	O
all	O
arguments	O
and	O
options	O
,	O
but	O
some	O
can	O
be	O
run	O
together	O
,	O
e.g.	O
</s>
<s>
-lS	O
is	O
the	O
same	O
as	O
-l	O
-S	O
.	O
Data	B-Operating_System
General	I-Operating_System
RDOS	I-Operating_System
CLI	O
list/e/s	O
04-26-80/b	O
List	O
/S/E	O
4-26-80/B	O
list	O
every	O
attribute	O
for	O
files	O
created	O
before	O
26	O
April	O
1980.Note	O
the	O
/B	O
at	O
the	O
end	O
of	O
the	O
date	O
argument	O
is	O
a	O
local	O
switch	O
,	O
that	O
modifies	O
the	O
meaning	O
of	O
that	O
argument	O
,	O
while	O
/S	O
and	O
/E	O
are	O
global	O
switches	O
,	O
i.e.	O
</s>
<s>
apply	O
to	O
the	O
whole	O
command	B-Application
.	O
</s>
<s>
In	O
Multics	B-Application
,	O
command-line	B-Application
options	O
and	O
subsystem	O
keywords	O
may	O
be	O
abbreviated	O
.	O
</s>
<s>
This	O
idea	O
appears	O
to	O
derive	O
from	O
the	O
PL/I	B-Language
programming	I-Language
language	I-Language
,	O
with	O
its	O
shortened	O
keywords	O
(	O
e.g.	O
,	O
STRG	O
for	O
STRINGRANGE	O
and	O
DCL	B-Operating_System
for	O
DECLARE	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
Multics	B-Application
"	O
forum	O
"	O
subsystem	O
,	O
the	O
-long_subject	O
parameter	O
can	O
be	O
abbreviated	O
-lgsj	O
.	O
</s>
<s>
It	O
is	O
also	O
common	O
for	O
Multics	B-Application
commands	O
to	O
be	O
abbreviated	O
,	O
typically	O
corresponding	O
to	O
the	O
initial	O
letters	O
of	O
the	O
words	O
that	O
are	O
strung	O
together	O
with	O
underscores	O
to	O
form	O
command	B-Application
names	O
,	O
such	O
as	O
the	O
use	O
of	O
did	O
for	O
delete_iacl_dir	O
.	O
</s>
<s>
In	O
some	O
other	O
systems	O
abbreviations	O
are	O
automatic	O
,	O
such	O
as	O
permitting	O
enough	O
of	O
the	O
first	O
characters	O
of	O
a	O
command	B-Application
name	O
to	O
uniquely	O
identify	O
it	O
(	O
such	O
as	O
SU	O
as	O
an	O
abbreviation	O
for	O
SUPERUSER	B-Application
)	O
while	O
others	O
may	O
have	O
some	O
specific	O
abbreviations	O
pre-programmed	O
(	O
e.g.	O
</s>
<s>
MD	B-Application
for	O
MKDIR	B-Application
in	O
COMMAND.COM	B-Operating_System
)	O
or	O
user-defined	O
via	O
batch	B-General_Concept
scripts	O
and	O
aliases	O
(	O
e.g.	O
</s>
<s>
alias	B-Device
md	B-Application
mkdir	B-Application
in	O
tcsh	B-Language
)	O
.	O
</s>
<s>
On	O
DOS	B-Device
,	O
OS/2	B-Application
and	O
Windows	O
,	O
different	O
programs	O
called	O
from	O
their	O
COMMAND.COM	B-Operating_System
or	O
CMD.EXE	B-Device
(	O
or	O
internal	O
their	O
commands	O
)	O
may	O
use	O
different	O
syntax	O
within	O
the	O
same	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
In	O
DOS	B-Device
,	O
OS/2	B-Application
and	O
Windows	O
,	O
the	O
forward	O
slash	O
(	O
/	O
)	O
is	O
most	O
prevalent	O
,	O
although	O
the	O
hyphen-minus	O
is	O
also	O
sometimes	O
used	O
.	O
</s>
<s>
In	O
many	O
versions	O
of	O
DOS	B-Device
(	O
MS-DOS/PCDOS	O
2.xx	O
and	O
higher	O
,	O
all	O
versions	O
of	O
DR-DOS	B-Application
since	O
5.0	O
,	O
as	O
well	O
as	O
PTS-DOS	B-Operating_System
,	O
Embedded	O
DOS	B-Device
,	O
FreeDOS	B-Application
and	O
RxDOS	O
)	O
the	O
switch	O
character	O
(	O
sometimes	O
abbreviated	O
switchar	B-Device
or	O
switchchar	O
)	O
to	O
be	O
used	O
is	O
defined	O
by	O
a	O
value	O
returned	O
from	O
a	O
system	B-Operating_System
call	I-Operating_System
(	O
INT	O
21h/AX	O
=	O
3700h	O
)	O
.	O
</s>
<s>
The	O
default	B-General_Concept
character	O
returned	O
by	O
this	O
API	B-Application
is	O
/	O
,	O
but	O
can	O
be	O
changed	O
to	O
a	O
hyphen-minus	O
on	O
the	O
above-mentioned	O
systems	O
,	O
except	O
for	O
under	O
Datalight	O
ROM-DOS	B-Operating_System
and	O
MS-DOS/PCDOS	O
5.0	O
and	O
higher	O
,	O
which	O
always	O
return	O
/	O
from	O
this	O
call	O
(	O
unless	O
one	O
of	O
many	O
available	O
TSRs	O
to	O
reenable	O
the	O
SwitChar	B-Device
feature	O
is	O
loaded	O
)	O
.	O
</s>
<s>
In	O
some	O
of	O
these	O
systems	O
(	O
MS-DOS/PCDOS	O
2.xx	O
,	O
DOS	B-Device
Plus	O
2.1	O
,	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
,	O
PTS-DOS	B-Operating_System
,	O
Embedded	O
DOS	B-Device
,	O
FreeDOS	B-Application
and	O
RxDOS	O
)	O
,	O
the	O
setting	O
can	O
also	O
be	O
pre-configured	O
by	O
a	O
SWITCHAR	B-Device
directive	O
in	O
CONFIG.SYS	B-Device
.	O
</s>
<s>
General	O
Software	O
's	O
Embedded	O
DOS	B-Device
provides	O
a	O
SWITCH	O
command	B-Application
for	O
the	O
same	O
purpose	O
,	O
whereas	O
4DOS	B-Application
allows	O
the	O
setting	O
to	O
be	O
changed	O
via	O
SETDOS	O
/W:n	O
.	O
Under	O
DR-DOS	B-Application
,	O
if	O
the	O
setting	O
has	O
been	O
changed	O
from	O
/	O
,	O
the	O
first	O
directory	O
separator	B-Algorithm
\	O
in	O
the	O
display	O
of	O
the	O
PROMPT	O
parameter	O
$G	O
will	O
change	O
to	O
a	O
forward	O
slash	O
/	O
(	O
which	O
is	O
also	O
a	O
valid	O
directory	O
separator	B-Algorithm
in	O
DOS	B-Device
,	O
FlexOS	B-Operating_System
,	O
4680	B-Language
OS	I-Language
,	O
4690	B-Language
OS	I-Language
,	O
OS/2	B-Application
and	O
Windows	O
)	O
thereby	O
serving	O
as	O
a	O
visual	O
clue	O
to	O
indicate	O
the	O
change	O
.	O
</s>
<s>
Also	O
,	O
the	O
current	O
setting	O
is	O
reflected	O
also	O
in	O
the	O
built-in	O
help	B-Protocol
screens	O
.	O
</s>
<s>
Some	O
versions	O
of	O
DR-DOS	B-Application
COMMAND.COM	B-Operating_System
also	O
support	O
a	O
PROMPT	O
token	O
$	O
/	O
to	O
display	O
the	O
current	O
setting	O
.	O
</s>
<s>
COMMAND.COM	B-Operating_System
since	O
DR-DOS	B-Application
7.02	O
also	O
provides	O
a	O
pseudo-environment	O
variable	O
named	O
%	O
/	O
%	O
to	O
allow	O
portable	O
batchjobs	B-General_Concept
to	O
be	O
written	O
.	O
</s>
<s>
Several	O
external	O
DR-DOS	B-Application
commands	O
additionally	O
support	O
an	O
environment	O
variable	O
%SWITCHAR%	O
to	O
override	O
the	O
system	O
setting	O
.	O
</s>
<s>
However	O
,	O
many	O
programs	O
are	O
hardwired	O
to	O
use	O
/	O
only	O
,	O
rather	O
than	O
retrieving	O
the	O
switch	O
setting	O
before	O
parsing	O
command-line	B-Application
arguments	O
.	O
</s>
<s>
A	O
very	O
small	O
number	O
,	O
mainly	O
ports	O
from	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
are	O
programmed	O
to	O
accept	O
"	O
-	O
"	O
even	O
if	O
the	O
switch	O
character	O
is	O
not	O
set	O
to	O
it	O
(	O
for	O
example	O
netstat	B-Application
and	O
ping	B-Protocol
,	O
supplied	O
with	O
Microsoft	B-Application
Windows	I-Application
,	O
will	O
accept	O
the	O
/	O
?	O
</s>
<s>
In	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
the	O
ASCII	O
hyphen-minus	O
begins	O
options	O
;	O
the	O
new	O
(	O
and	O
GNU	B-Operating_System
)	O
convention	O
is	O
to	O
use	O
two	O
hyphens	O
then	O
a	O
word	O
(	O
e.g.	O
</s>
<s>
--create	O
)	O
to	O
identify	O
the	O
option	O
's	O
use	O
while	O
the	O
old	O
convention	O
(	O
and	O
still	O
available	O
as	O
an	O
option	O
for	O
frequently-used	O
options	O
)	O
is	O
to	O
use	O
one	O
hyphen	O
then	O
one	O
letter	O
(	O
e.g.	O
,	O
-c	O
)	O
;	O
if	O
one	O
hyphen	O
is	O
followed	O
by	O
two	O
or	O
more	O
letters	O
it	O
may	O
mean	O
two	O
options	O
are	O
being	O
specified	O
,	O
or	O
it	O
may	O
mean	O
the	O
second	O
and	O
subsequent	O
letters	O
are	O
a	O
parameter	O
(	O
such	O
as	O
filename	O
or	O
date	O
)	O
for	O
the	O
first	O
option	O
.	O
</s>
<s>
Two	O
hyphen-minus	O
characters	O
without	O
following	O
letters	O
(	O
--	O
)	O
may	O
indicate	O
that	O
the	O
remaining	O
arguments	O
should	O
not	O
be	O
treated	O
as	O
options	O
,	O
which	O
is	O
useful	O
for	O
example	O
if	O
a	O
file	B-Operating_System
name	O
itself	O
begins	O
with	O
a	O
hyphen	O
,	O
or	O
if	O
further	O
arguments	O
are	O
meant	O
for	O
an	O
inner	O
command	B-Application
(	O
e.g.	O
,	O
sudo	B-Device
)	O
.	O
</s>
<s>
This	O
is	O
a	O
common	O
feature	O
of	O
GNU	B-Operating_System
software	O
.	O
</s>
<s>
The	O
getopt	B-Library
function	O
and	O
program	O
,	O
and	O
the	O
getopts	B-Device
command	B-Application
are	O
usually	O
used	O
for	O
parsing	O
command-line	B-Application
options	O
.	O
</s>
<s>
Unix	B-Application
command	B-Application
names	O
,	O
arguments	O
and	O
options	O
are	O
case-sensitive	O
(	O
except	O
in	O
a	O
few	O
examples	O
,	O
mainly	O
where	O
popular	O
commands	O
from	O
other	O
operating	B-General_Concept
systems	I-General_Concept
have	O
been	O
ported	O
to	O
Unix	B-Application
)	O
.	O
</s>
<s>
FlexOS	B-Operating_System
,	O
4680	B-Language
OS	I-Language
and	O
4690	B-Language
OS	I-Language
use	O
-	O
.	O
</s>
<s>
CP/M	B-Application
typically	O
used	O
[	O
.	O
</s>
<s>
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
)	O
uses	O
a	O
single	O
left	O
parenthesis	O
to	O
separate	O
options	O
at	O
the	O
end	O
of	O
the	O
command	B-Application
from	O
the	O
other	O
arguments	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
following	O
command	B-Application
the	O
options	O
indicate	O
that	O
the	O
target	O
file	B-Operating_System
should	O
be	O
replaced	O
if	O
it	O
exists	O
,	O
and	O
the	O
date	O
and	O
time	O
of	O
the	O
source	O
file	B-Operating_System
should	O
be	O
retained	O
on	O
the	O
copy	O
:	O
</s>
<s>
Data	O
General	O
's	O
CLI	O
under	O
their	O
RDOS	B-Operating_System
,	O
AOS	O
,	O
etc	O
.	O
</s>
<s>
operating	B-General_Concept
systems	I-General_Concept
,	O
as	O
well	O
as	O
the	O
version	O
of	O
CLI	O
that	O
came	O
with	O
their	O
Business	B-Language
Basic	I-Language
,	O
uses	O
only	O
/	O
as	O
the	O
switch	O
character	O
,	O
is	O
case-insensitive	O
,	O
and	O
allows	O
"	O
local	O
switches	O
"	O
on	O
some	O
arguments	O
to	O
control	O
the	O
way	O
they	O
are	O
interpreted	O
,	O
such	O
as	O
MAC/U	O
LIB/S	O
A	O
B	O
C	B-Language
$	O
LPT/L	O
has	O
the	O
global	O
option	O
"	O
U	O
"	O
to	O
the	O
macro	O
assembler	O
command	B-Application
to	O
append	O
user	O
symbols	O
,	O
but	O
two	O
local	O
switches	O
,	O
one	O
to	O
specify	O
LIB	O
should	O
be	O
skipped	O
on	O
pass	O
2	O
and	O
the	O
other	O
to	O
direct	O
listing	O
to	O
the	O
printer	O
,	O
$LPT	O
.	O
</s>
<s>
In	O
contrast	O
,	O
GUIs	B-Application
usually	O
inform	O
the	O
user	O
of	O
available	O
actions	O
with	O
menus	O
,	O
icons	O
,	O
or	O
other	O
visual	O
cues	O
.	O
</s>
<s>
To	O
overcome	O
this	O
limitation	O
,	O
many	O
CLI	O
programs	O
display	O
a	O
usage	B-Protocol
message	I-Protocol
,	O
typically	O
when	O
invoked	O
with	O
no	O
arguments	O
or	O
one	O
of	O
?,	O
-	O
?,	O
-h	O
,	O
-H	O
,	O
/	O
?,	O
/h	O
,	O
/H	O
,	O
/Help	O
,	O
-help	O
,	O
or	O
--help	O
.	O
</s>
<s>
However	O
,	O
entering	O
a	O
program	O
name	O
without	O
parameters	O
in	O
the	O
hope	O
that	O
it	O
will	O
display	O
usage	O
help	B-Protocol
can	O
be	O
hazardous	O
,	O
as	O
programs	O
and	O
scripts	O
for	O
which	O
command	B-Application
line	I-Application
arguments	O
are	O
optional	O
will	O
execute	O
without	O
further	O
notice	O
.	O
</s>
<s>
Although	O
desirable	O
at	O
least	O
for	O
the	O
help	B-Protocol
parameter	O
,	O
programs	O
may	O
not	O
support	O
all	O
option	O
lead-in	O
characters	O
exemplified	O
above	O
.	O
</s>
<s>
Under	O
DOS	B-Device
,	O
where	O
the	O
default	B-General_Concept
command-line	B-Application
option	O
character	O
can	O
be	O
changed	O
from	O
/	O
to	O
-	O
,	O
programs	O
may	O
query	O
the	O
SwitChar	B-Device
API	B-Application
in	O
order	O
to	O
determine	O
the	O
current	O
setting	O
.	O
</s>
<s>
So	O
,	O
if	O
a	O
program	O
is	O
not	O
hardwired	O
to	O
support	O
them	O
all	O
,	O
a	O
user	O
may	O
need	O
to	O
know	O
the	O
current	O
setting	O
even	O
to	O
be	O
able	O
to	O
reliably	O
request	O
help	B-Protocol
.	O
</s>
<s>
If	O
the	O
SwitChar	B-Device
has	O
been	O
changed	O
to	O
-	O
and	O
therefore	O
the	O
/	O
character	O
is	O
accepted	O
as	O
alternative	O
path	B-Application
delimiter	B-Algorithm
also	O
at	O
the	O
DOS	B-Device
command	B-Application
line	I-Application
,	O
programs	O
may	O
misinterpret	O
options	O
like	O
/h	O
or	O
/H	O
as	O
paths	O
rather	O
than	O
help	B-Protocol
parameters	O
.	O
</s>
<s>
However	O
,	O
if	O
given	O
as	O
first	O
or	O
only	O
parameter	O
,	O
most	O
DOS	B-Device
programs	O
will	O
,	O
by	O
convention	O
,	O
accept	O
it	O
as	O
request	O
for	O
help	B-Protocol
regardless	O
of	O
the	O
current	O
SwitChar	B-Device
setting	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
different	O
levels	O
of	O
help	B-Protocol
can	O
be	O
selected	O
for	O
a	O
program	O
.	O
</s>
<s>
Some	O
programs	O
supporting	O
this	O
allow	O
to	O
give	O
a	O
verbosity	O
level	O
as	O
an	O
optional	O
argument	O
to	O
the	O
help	B-Protocol
parameter	O
(	O
as	O
in	O
/H:1	O
,	O
/H:2	O
,	O
etc	O
.	O
)	O
</s>
<s>
or	O
they	O
give	O
just	O
a	O
short	O
help	B-Protocol
on	O
help	B-Protocol
parameters	O
with	O
question	O
mark	O
and	O
a	O
longer	O
help	B-Protocol
screen	O
for	O
the	O
other	O
help	B-Protocol
options	O
.	O
</s>
<s>
Depending	O
on	O
the	O
program	O
,	O
additional	O
or	O
more	O
specific	O
help	B-Protocol
on	O
accepted	O
parameters	O
is	O
sometimes	O
available	O
by	O
either	O
providing	O
the	O
parameter	O
in	O
question	O
as	O
an	O
argument	O
to	O
the	O
help	B-Protocol
parameter	O
or	O
vice	O
versa	O
(	O
as	O
in	O
/H:W	O
or	O
in	O
/W	O
:	O
?	O
</s>
<s>
In	O
a	O
similar	O
fashion	O
to	O
the	O
help	B-Protocol
parameter	O
,	O
but	O
much	O
less	O
common	O
,	O
some	O
programs	O
provide	O
additional	O
information	O
about	O
themselves	O
(	O
like	O
mode	B-General_Concept
,	O
status	O
,	O
version	O
,	O
author	O
,	O
license	O
or	O
contact	O
information	O
)	O
when	O
invoked	O
with	O
an	O
"	O
about	O
"	O
parameter	O
like	O
-	O
!,	O
/	O
!,	O
-about	O
,	O
or	O
--about	O
.	O
</s>
<s>
characters	O
typically	O
also	O
serve	O
other	O
purposes	O
at	O
the	O
command	B-Application
line	I-Application
,	O
they	O
may	O
not	O
be	O
available	O
in	O
all	O
scenarios	O
,	O
therefore	O
,	O
they	O
should	O
not	O
be	O
the	O
only	O
options	O
to	O
access	O
the	O
corresponding	O
help	B-Protocol
information	O
.	O
</s>
<s>
If	O
more	O
detailed	O
help	B-Protocol
is	O
necessary	O
than	O
provided	O
by	O
a	O
program	O
's	O
built-in	O
internal	O
help	B-Protocol
,	O
many	O
systems	O
support	O
a	O
dedicated	O
external	O
"	O
help	B-Protocol
command	B-Application
"	O
command	B-Application
(	O
or	O
similar	O
)	O
,	O
which	O
accepts	O
a	O
command	B-Application
name	O
as	O
calling	O
parameter	O
and	O
will	O
invoke	O
an	O
external	O
help	B-Protocol
system	O
.	O
</s>
<s>
In	O
the	O
DR-DOS	B-Application
family	O
,	O
typing	O
/	O
?	O
</s>
<s>
or	O
/H	O
at	O
the	O
COMMAND.COM	B-Operating_System
prompt	O
instead	O
of	O
a	O
command	B-Application
itself	O
will	O
display	O
a	O
dynamically	O
generated	O
list	O
of	O
available	O
internal	O
commands	O
;	O
4DOS	B-Application
and	O
NDOS	B-Application
support	O
the	O
same	O
feature	O
by	O
typing	O
?	O
</s>
<s>
at	O
the	O
prompt	O
(	O
which	O
is	O
also	O
accepted	O
by	O
newer	O
versions	O
of	O
DR-DOS	B-Application
COMMAND.COM	B-Operating_System
)	O
;	O
internal	O
commands	O
can	O
be	O
individually	O
disabled	O
or	O
reenabled	O
via	O
SETDOS	O
/I	O
.	O
</s>
<s>
In	O
addition	O
to	O
this	O
,	O
some	O
newer	O
versions	O
of	O
DR-DOS	B-Application
COMMAND.COM	B-Operating_System
also	O
accept	O
a	O
?	O
%	O
command	B-Application
to	O
display	O
a	O
list	O
of	O
available	O
built-in	O
pseudo-environment	O
variables	O
.	O
</s>
<s>
Besides	O
their	O
purpose	O
as	O
quick	O
help	B-Protocol
reference	O
this	O
can	O
be	O
used	O
in	O
batchjobs	B-General_Concept
to	O
query	O
the	O
facilities	O
of	O
the	O
underlying	O
command-line	B-Application
processor	O
.	O
</s>
<s>
Built-in	O
usage	O
help	B-Protocol
and	O
man	B-Protocol
pages	I-Protocol
commonly	O
employ	O
a	O
small	O
syntax	O
to	O
describe	O
the	O
valid	O
command	B-Application
form	O
:	O
</s>
<s>
Notice	O
that	O
these	O
characters	O
have	O
different	O
meanings	O
than	O
when	O
used	O
directly	O
in	O
the	O
shell	B-Application
.	O
</s>
<s>
In	O
many	O
areas	O
of	O
computing	O
,	O
but	O
particularly	O
in	O
the	O
command	B-Application
line	I-Application
,	O
the	O
space	O
character	O
can	O
cause	O
problems	O
as	O
it	O
has	O
two	O
distinct	O
and	O
incompatible	O
functions	O
:	O
as	O
part	O
of	O
a	O
command	B-Application
or	O
parameter	O
,	O
or	O
as	O
a	O
parameter	O
or	O
name	O
separator	B-Algorithm
.	O
</s>
<s>
Ambiguity	O
can	O
be	O
prevented	O
either	O
by	O
prohibiting	O
embedded	O
spaces	O
in	O
file	B-Operating_System
and	O
directory	O
names	O
in	O
the	O
first	O
place	O
(	O
for	O
example	O
,	O
by	O
substituting	O
them	O
with	O
underscores	O
_	O
)	O
,	O
or	O
by	O
enclosing	O
a	O
name	O
with	O
embedded	O
spaces	O
between	O
quote	O
characters	O
or	O
using	O
an	O
escape	B-Algorithm
character	I-Algorithm
before	O
the	O
space	O
,	O
usually	O
a	O
backslash	O
(	O
\	O
)	O
.	O
</s>
<s>
Long	O
path/Long	O
program	O
name	O
Parameter	O
one	O
Parameter	O
two	O
…	O
</s>
<s>
"	O
Long	O
path/Long	O
program	O
name	O
"	O
"	O
Parameter	O
one	O
"	O
"	O
Parameter	O
two	O
"	O
…	O
</s>
<s>
Long	O
\	O
path/Long	O
\	O
program	O
\	O
name	O
Parameter	O
\	O
one	O
Parameter	O
\	O
two	O
…	O
</s>
<s>
Unix-based	O
operating	B-General_Concept
systems	I-General_Concept
minimize	O
the	O
use	O
of	O
embedded	O
spaces	O
to	O
minimize	O
the	O
need	O
for	O
quotes	O
.	O
</s>
<s>
In	O
Microsoft	B-Application
Windows	I-Application
,	O
one	O
often	O
has	O
to	O
use	O
quotes	O
because	O
embedded	O
spaces	O
(	O
such	O
as	O
in	O
directory	O
names	O
)	O
are	O
common	O
.	O
</s>
<s>
The	O
term	O
command-line	B-Application
interpreter	B-Application
(	O
CLI	O
)	O
is	O
applied	O
to	O
computer	B-Application
programs	I-Application
designed	O
to	O
interpret	B-Application
a	O
sequence	O
of	O
lines	O
of	O
text	O
which	O
may	O
be	O
entered	O
by	O
a	O
user	O
,	O
read	O
from	O
a	O
file	B-Operating_System
or	O
another	O
kind	O
of	O
data	B-General_Concept
stream	I-General_Concept
.	O
</s>
<s>
The	O
context	O
of	O
interpretation	O
is	O
usually	O
one	O
of	O
a	O
given	O
operating	B-General_Concept
system	I-General_Concept
or	O
programming	O
language	O
.	O
</s>
<s>
Command-line	B-Application
interpreters	B-Application
allow	O
users	O
to	O
issue	O
various	O
commands	O
in	O
a	O
very	O
efficient	O
(	O
and	O
often	O
terse	O
)	O
way	O
.	O
</s>
<s>
The	O
Unix	B-Application
#	O
!	O
</s>
<s>
mechanism	O
and	O
OS/2	B-Application
EXTPROC	O
command	B-Application
facilitate	O
the	O
passing	O
of	O
batch	B-General_Concept
files	O
to	O
external	O
processors	O
.	O
</s>
<s>
One	O
can	O
use	O
these	O
mechanisms	O
to	O
write	O
specific	O
command	B-Application
processors	O
for	O
dedicated	O
uses	O
,	O
and	O
process	O
external	O
data	O
files	O
which	O
reside	O
in	O
batch	B-General_Concept
files	O
.	O
</s>
<s>
Many	O
graphical	B-Application
interfaces	I-Application
,	O
such	O
as	O
the	O
OS/2	B-Device
Presentation	I-Device
Manager	I-Device
and	O
early	O
versions	O
of	O
Microsoft	B-Application
Windows	I-Application
use	O
command-lines	B-Application
to	O
call	O
helper	O
programs	O
to	O
open	O
documents	O
and	O
programs	O
.	O
</s>
<s>
The	O
commands	O
are	O
stored	O
in	O
the	O
graphical	O
shell	B-Application
or	O
in	O
files	O
like	O
the	O
registry	O
or	O
the	O
OS/2	B-Application
OS2USER.INI	O
file	B-Operating_System
.	O
</s>
<s>
The	O
earliest	O
computers	O
did	O
not	O
support	O
interactive	O
input/output	O
devices	O
,	O
often	O
relying	O
on	O
sense	B-Device
switches	I-Device
and	O
lights	O
to	O
communicate	O
with	O
the	O
computer	O
operator	O
.	O
</s>
<s>
This	O
was	O
adequate	O
for	O
batch	B-General_Concept
systems	I-General_Concept
that	O
ran	O
one	O
program	O
at	O
a	O
time	O
,	O
often	O
with	O
the	O
programmer	O
acting	O
as	O
operator	O
.	O
</s>
<s>
Later	O
a	O
single	O
system	B-Device
console	I-Device
was	O
added	O
to	O
allow	O
the	O
operator	O
to	O
communicate	O
with	O
the	O
system	O
.	O
</s>
<s>
From	O
the	O
1960s	O
onwards	O
,	O
user	O
interaction	O
with	O
computers	O
was	O
primarily	O
by	O
means	O
of	O
command-line	B-Application
interfaces	I-Application
,	O
initially	O
on	O
machines	O
like	O
the	O
Teletype	B-Application
Model	I-Application
33	I-Application
ASR	O
,	O
but	O
then	O
on	O
early	O
CRT-based	O
computer	B-General_Concept
terminals	I-General_Concept
such	O
as	O
the	O
VT52	B-Application
.	O
</s>
<s>
All	O
of	O
these	O
devices	O
were	O
purely	O
text	B-Application
based	I-Application
,	O
with	O
no	O
ability	O
to	O
display	O
graphic	O
or	O
pictures	O
.	O
</s>
<s>
For	O
business	O
application	B-Application
programs	I-Application
,	O
text-based	B-Application
menus	O
were	O
used	O
,	O
but	O
for	O
more	O
general	O
interaction	O
the	O
command	B-Application
line	I-Application
was	O
the	O
interface	O
.	O
</s>
<s>
Around	O
1964	O
Louis	O
Pouzin	O
introduced	O
the	O
concept	O
and	O
the	O
name	O
shell	B-Application
in	O
Multics	B-Application
,	O
building	O
on	O
earlier	O
,	O
simpler	O
facilities	O
in	O
the	O
Compatible	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
(	O
CTSS	O
)	O
.	O
</s>
<s>
From	O
the	O
early	O
1970s	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
adapted	O
the	O
concept	O
of	O
a	O
powerful	O
command-line	B-Application
environment	O
,	O
and	O
introduced	O
the	O
ability	O
to	O
pipe	B-Operating_System
the	O
output	O
of	O
one	O
command	B-Application
in	O
as	O
input	O
to	O
another	O
.	O
</s>
<s>
Unix	B-Application
also	O
had	O
the	O
capability	O
to	O
save	O
and	O
re-run	O
strings	O
of	O
commands	O
as	O
"	O
shell	B-Language
scripts	I-Language
"	O
which	O
acted	O
like	O
custom	O
commands	O
.	O
</s>
<s>
The	O
command-line	B-Application
was	O
also	O
the	O
main	O
interface	O
for	O
the	O
early	O
home	O
computers	O
such	O
as	O
the	O
Commodore	B-Device
PET	I-Device
,	O
Apple	B-Device
II	I-Device
and	O
BBC	B-Device
Micro	I-Device
–	O
almost	O
always	O
in	O
the	O
form	O
of	O
a	O
BASIC	O
interpreter	B-Application
.	O
</s>
<s>
When	O
more	O
powerful	O
business	O
oriented	O
microcomputers	O
arrived	O
with	O
CP/M	B-Application
and	O
later	O
DOS	B-Device
computers	O
such	O
as	O
the	O
IBM	B-Device
PC	I-Device
,	O
the	O
command-line	B-Application
began	O
to	O
borrow	O
some	O
of	O
the	O
syntax	O
and	O
features	O
of	O
the	O
Unix	B-Application
shells	I-Application
such	O
as	O
globbing	B-Language
and	O
piping	B-Operating_System
of	O
output	O
.	O
</s>
<s>
The	O
command-line	B-Application
was	O
first	O
seriously	O
challenged	O
by	O
the	O
PARC	O
GUI	B-Application
approach	O
used	O
in	O
the	O
1983	O
Apple	B-Device
Lisa	I-Device
and	O
the	O
1984	O
Apple	B-Device
Macintosh	I-Device
.	O
</s>
<s>
A	O
few	O
computer	O
users	O
used	O
GUIs	B-Application
such	O
as	O
GEOS	B-Application
and	O
Windows	B-Application
3.1	I-Application
but	O
the	O
majority	O
of	O
IBM	B-Device
PC	I-Device
users	O
did	O
not	O
replace	O
their	O
COMMAND.COM	B-Operating_System
shell	B-Application
with	O
a	O
GUI	B-Application
until	O
Windows	B-Application
95	I-Application
was	O
released	O
in	O
1995	O
.	O
</s>
<s>
While	O
most	O
non-expert	O
computer	O
users	O
now	O
use	O
a	O
GUI	B-Application
almost	O
exclusively	O
,	O
more	O
advanced	O
users	O
have	O
access	O
to	O
powerful	O
command-line	B-Application
environments	O
:	O
</s>
<s>
The	O
default	B-General_Concept
VAX/VMS	B-Operating_System
command	B-Application
shell	B-Application
,	O
using	O
the	O
DCL	B-Operating_System
language	O
,	O
has	O
been	O
ported	O
to	O
Windows	O
systems	O
at	O
least	O
three	O
times	O
,	O
including	O
PC-DCL	O
and	O
Acceler8	O
DCL	B-Operating_System
Lite	O
.	O
</s>
<s>
Unix	B-Application
command	B-Operating_System
shells	I-Operating_System
have	O
been	O
ported	O
to	O
VMS	B-Operating_System
and	O
DOS/Windows	O
95	O
and	O
Windows	B-Device
NT	I-Device
types	O
of	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
COMMAND.COM	B-Operating_System
is	O
the	O
command-line	B-Application
interpreter	B-Application
of	O
MS-DOS	B-Application
,	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
,	O
and	O
clones	O
such	O
as	O
DR-DOS	B-Application
,	O
SISNE	B-Operating_System
plus	I-Operating_System
,	O
PTS-DOS	B-Operating_System
,	O
ROM-DOS	B-Operating_System
,	O
and	O
FreeDOS	B-Application
.	O
</s>
<s>
IBM	B-Application
OS/2	I-Application
(	O
and	O
derivatives	O
such	O
as	O
eComStation	B-Device
and	O
ArcaOS	B-Device
)	O
has	O
the	O
cmd.exe	B-Device
processor	O
.	O
</s>
<s>
This	O
copies	O
the	O
COMMAND.COM	B-Operating_System
commands	O
,	O
with	O
extensions	O
to	O
REXX	B-Language
.	O
</s>
<s>
cmd.exe	B-Device
is	O
part	O
of	O
the	O
Windows	B-Device
NT	I-Device
stream	O
of	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Yet	O
another	O
cmd.exe	B-Device
is	O
a	O
stripped-down	O
shell	B-Application
for	O
Windows	B-Operating_System
CE	I-Operating_System
3.0	O
.	O
</s>
<s>
An	O
MS-DOS	B-Application
type	O
interpreter	B-Application
called	O
PocketDOS	O
has	O
been	O
ported	O
to	O
Windows	B-Operating_System
CE	I-Operating_System
machines	O
;	O
the	O
most	O
recent	O
release	O
is	O
almost	O
identical	O
to	O
MS-DOS	B-Application
6.22	O
and	O
can	O
also	O
run	O
Windows	O
1	O
,	O
2	O
,	O
and	O
3.0	O
,	O
QBasic	B-Language
and	O
other	O
development	O
tools	O
,	O
4NT	B-Application
and	O
4DOS	B-Application
.	O
</s>
<s>
The	O
latest	O
release	O
includes	O
several	O
shells	O
,	O
namely	O
MS-DOS	B-Application
6.22	O
,	O
PCDOS	B-Operating_System
7	O
,	O
DRDOS	B-Application
3.xx	O
,	O
and	O
others	O
.	O
</s>
<s>
Windows	O
users	O
might	O
use	O
the	O
CScript	O
interface	O
to	O
alternate	O
programs	O
,	O
from	O
command-line	B-Application
.	O
</s>
<s>
PowerShell	B-Application
provides	O
a	O
command-line	B-Application
interface	I-Application
,	O
but	O
its	O
applets	O
are	O
not	O
written	O
in	O
Shell	B-Language
script	I-Language
.	O
</s>
<s>
Implementations	O
of	O
the	O
Unix	B-Application
shell	I-Application
are	O
also	O
available	O
as	O
part	O
of	O
the	O
POSIX	B-Device
sub-system	I-Device
,	O
Cygwin	B-Language
,	O
MKS	B-Application
Toolkit	I-Application
,	O
UWIN	B-Application
,	O
Hamilton	B-Device
C	I-Device
shell	I-Device
and	O
other	O
software	B-Architecture
packages	I-Architecture
.	O
</s>
<s>
Implementations	O
of	O
PHP	B-Application
have	O
a	O
shell	B-Application
for	O
interactive	O
use	O
called	O
php-cli	O
.	O
</s>
<s>
Standard	O
Tcl/Tk	B-Application
has	O
two	O
interactive	O
shells	O
,	O
Tclsh	O
and	O
Wish	O
,	O
the	O
latter	O
being	O
the	O
GUI	B-Application
version	O
.	O
</s>
<s>
Python	B-Language
,	O
Ruby	B-Language
,	O
Lua	B-Language
,	O
XLNT	B-Language
,	O
and	O
other	O
interpreters	B-Application
also	O
have	O
command	B-Operating_System
shells	I-Operating_System
for	O
interactive	O
use	O
.	O
</s>
<s>
FreeBSD	B-Operating_System
uses	O
tcsh	B-Language
as	O
its	O
default	B-General_Concept
interactive	O
shell	B-Application
for	O
the	O
superuser	B-Application
,	O
and	O
ash	B-Operating_System
as	O
default	B-General_Concept
scripting	B-Language
shell	B-Application
.	O
</s>
<s>
Many	O
Linux	B-Application
distributions	I-Application
have	O
the	O
Bash	B-Operating_System
implementation	O
of	O
the	O
Unix	B-Application
shell	I-Application
.	O
</s>
<s>
Apple	O
macOS	B-Application
and	O
some	O
Linux	B-Application
distributions	I-Application
use	O
zsh	B-Application
.	O
</s>
<s>
Previously	O
,	O
macOS	B-Application
used	O
tcsh	B-Language
and	O
Bash	B-Operating_System
.	O
</s>
<s>
Embedded	B-Application
Linux	I-Application
(	O
and	O
other	O
embedded	O
Unix-like	B-Operating_System
)	O
devices	O
often	O
use	O
the	O
Ash	B-Operating_System
implementation	O
of	O
the	O
Unix	B-Application
shell	I-Application
,	O
as	O
part	O
of	O
Busybox	B-Application
.	O
</s>
<s>
Android	B-Application
uses	O
the	O
mksh	B-Language
shell	B-Application
,	O
which	O
replaces	O
a	O
shell	B-Application
derived	O
from	O
ash	B-Operating_System
that	O
was	O
used	O
in	O
older	O
Android	B-Application
versions	O
,	O
supplemented	O
with	O
commands	O
from	O
the	O
separate	O
toolbox	O
binary	O
.	O
</s>
<s>
Routers	B-Protocol
with	O
Cisco	B-Protocol
IOS	I-Protocol
,	O
Junos	B-Application
and	O
many	O
others	O
are	O
commonly	O
configured	O
from	O
the	O
command	B-Application
line	I-Application
.	O
</s>
<s>
The	O
Plan	B-Operating_System
9	I-Operating_System
operating	B-General_Concept
system	I-General_Concept
uses	O
the	O
rc	O
shell	B-Application
which	O
is	O
similar	O
in	O
design	O
to	O
the	B-Device
Bourne	I-Device
shell	I-Device
.	O
</s>
<s>
Most	O
command-line	B-Application
interpreters	B-Application
support	O
scripting	B-Language
,	O
to	O
various	O
extents	O
.	O
</s>
<s>
(	O
They	O
are	O
,	O
after	O
all	O
,	O
interpreters	B-Application
of	O
an	O
interpreted	B-Application
programming	I-Application
language	I-Application
,	O
albeit	O
in	O
many	O
cases	O
the	O
language	O
is	O
unique	O
to	O
the	O
particular	O
command-line	B-Application
interpreter	B-Application
.	O
)	O
</s>
<s>
They	O
will	O
interpret	B-Application
scripts	O
(	O
variously	O
termed	O
shell	B-Language
scripts	I-Language
or	O
batch	B-General_Concept
files	O
)	O
written	O
in	O
the	O
language	O
that	O
they	O
interpret	B-Application
.	O
</s>
<s>
Some	O
command-line	B-Application
interpreters	B-Application
also	O
incorporate	O
the	O
interpreter	B-Application
engines	O
of	O
other	O
languages	O
,	O
such	O
as	O
REXX	B-Language
,	O
in	O
addition	O
to	O
their	O
own	O
,	O
allowing	O
the	O
executing	O
of	O
scripts	O
,	O
in	O
those	O
languages	O
,	O
directly	O
within	O
the	O
command-line	B-Application
interpreter	B-Application
itself	O
.	O
</s>
<s>
Conversely	O
,	O
scripting	B-Language
programming	I-Language
languages	I-Language
,	O
in	O
particular	O
those	O
with	O
an	O
eval	O
function	O
(	O
such	O
as	O
REXX	B-Language
,	O
Perl	B-Language
,	O
Python	B-Language
,	O
Ruby	B-Language
or	O
Jython	B-Language
)	O
,	O
can	O
be	O
used	O
to	O
implement	O
command-line	B-Application
interpreters	B-Application
and	O
filters	O
.	O
</s>
<s>
For	O
a	O
few	O
operating	B-General_Concept
systems	I-General_Concept
,	O
most	O
notably	O
DOS	B-Device
,	O
such	O
a	O
command	B-Application
interpreter	B-Application
provides	O
a	O
more	O
flexible	O
command-line	B-Application
interface	I-Application
than	O
the	O
one	O
supplied	O
.	O
</s>
<s>
In	O
other	O
cases	O
,	O
such	O
a	O
command	B-Application
interpreter	B-Application
can	O
present	O
a	O
highly	O
customised	O
user	O
interface	O
employing	O
the	O
user	O
interface	O
and	O
input/output	O
facilities	O
of	O
the	O
language	O
.	O
</s>
<s>
The	O
command	B-Application
line	I-Application
provides	O
an	O
interface	O
between	O
programs	O
as	O
well	O
as	O
the	O
user	O
.	O
</s>
<s>
In	O
this	O
sense	O
,	O
a	O
command	B-Application
line	I-Application
is	O
an	O
alternative	O
to	O
a	O
dialog	O
box	O
.	O
</s>
<s>
Editors	B-Application
and	O
databases	O
present	O
a	O
command	B-Application
line	I-Application
,	O
in	O
which	O
alternate	O
command	B-Application
processors	O
might	O
run	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
one	O
might	O
have	O
options	O
on	O
the	O
command	B-Application
line	I-Application
,	O
which	O
opens	O
a	O
dialog	O
box	O
.	O
</s>
<s>
The	O
latest	O
version	O
of	O
'	O
Take	B-Application
Command	I-Application
 '	O
has	O
this	O
feature	O
.	O
</s>
<s>
DBase	O
used	O
a	O
dialog	O
box	O
to	O
construct	O
command	B-Application
lines	I-Application
,	O
which	O
could	O
be	O
further	O
edited	O
before	O
use	O
.	O
</s>
<s>
Programs	O
like	O
BASIC	O
,	O
diskpart	B-Application
,	O
Edlin	B-Application
,	O
and	O
QBASIC	B-Language
all	O
provide	O
command-line	B-Application
interfaces	I-Application
,	O
some	O
of	O
which	O
use	O
the	O
system	B-Operating_System
shell	I-Operating_System
.	O
</s>
<s>
Basic	O
is	O
modeled	O
on	O
the	O
default	B-General_Concept
interface	O
for	O
8-bit	O
Intel	O
computers	O
.	O
</s>
<s>
Calculators	O
can	O
be	O
run	O
as	O
command-line	B-Application
or	O
dialog	O
interfaces	O
.	O
</s>
<s>
Emacs	B-Application
provides	O
a	O
command-line	B-Application
interface	I-Application
in	O
the	O
form	O
of	O
its	O
minibuffer	O
.	O
</s>
<s>
Commands	O
and	O
arguments	O
can	O
be	O
entered	O
using	O
Emacs	B-Application
standard	O
text	B-Application
editing	I-Application
support	O
,	O
and	O
output	O
is	O
displayed	O
in	O
another	O
buffer	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
text	O
mode	B-General_Concept
games	O
,	O
like	O
Adventure	B-Application
or	O
King	O
's	O
Quest	O
1-3	O
,	O
which	O
relied	O
on	O
the	O
user	O
typing	O
commands	O
at	O
the	O
bottom	O
of	O
the	O
screen	O
.	O
</s>
<s>
The	O
text	O
adventure	B-Application
The	B-Application
Hitchhiker	I-Application
's	I-Application
Guide	I-Application
to	I-Application
the	I-Application
Galaxy	I-Application
,	O
a	O
piece	O
of	O
interactive	O
fiction	O
based	O
on	O
Douglas	O
Adam	O
's	O
book	O
of	O
the	O
same	O
name	O
,	O
is	O
a	O
teletype-style	O
command-line	B-Application
game	O
.	O
</s>
<s>
The	O
most	O
notable	O
of	O
these	O
interfaces	O
is	O
the	O
standard	B-Operating_System
streams	I-Operating_System
interface	O
,	O
which	O
allows	O
the	O
output	O
of	O
one	O
command	B-Application
to	O
be	O
passed	O
to	O
the	O
input	O
of	O
another	O
.	O
</s>
<s>
This	O
provides	O
the	O
interfaces	O
of	O
piping	B-Operating_System
,	O
filters	O
and	O
redirection	B-Device
.	O
</s>
<s>
Under	O
Unix	B-Application
,	O
devices	B-Application
are	I-Application
files	I-Application
too	O
,	O
so	O
the	O
normal	O
type	O
of	O
file	B-Operating_System
for	O
the	O
shell	B-Application
used	O
for	O
stdin	O
,	O
stdout	O
and	O
stderr	O
is	O
a	O
tty	O
device	O
file	B-Operating_System
.	O
</s>
<s>
Another	O
command-line	B-Application
interface	I-Application
allows	O
a	O
shell	B-Application
program	O
to	O
launch	O
helper	O
programs	O
,	O
either	O
to	O
launch	O
documents	O
or	O
start	O
a	O
program	O
.	O
</s>
<s>
The	O
command	B-Application
is	O
processed	O
internally	O
by	O
the	O
shell	B-Application
,	O
and	O
then	O
passed	O
on	O
to	O
another	O
program	O
to	O
launch	O
the	O
document	O
.	O
</s>
<s>
The	O
graphical	B-Application
interface	I-Application
of	O
Windows	O
and	O
OS/2	B-Application
rely	O
heavily	O
on	O
command-lines	B-Application
passed	O
through	O
to	O
other	O
programs	O
–	O
console	O
or	O
graphical	O
,	O
which	O
then	O
usually	O
process	O
the	O
command	B-Application
line	I-Application
without	O
presenting	O
a	O
user-console	O
.	O
</s>
<s>
Programs	O
like	O
the	O
OS/2	B-Application
E	B-Application
editor	I-Application
and	O
some	O
other	O
IBM	O
editors	B-Application
,	O
can	O
process	O
command-lines	B-Application
normally	O
meant	O
for	O
the	O
shell	B-Application
,	O
the	O
output	O
being	O
placed	O
directly	O
in	O
the	O
document	O
window	O
.	O
</s>
<s>
A	O
web	O
browser	O
's	O
URL	O
input	O
field	O
can	O
be	O
used	O
as	O
a	O
command	B-Application
line	I-Application
.	O
</s>
<s>
It	O
can	O
be	O
used	O
to	O
"	O
launch	O
"	O
web	B-Application
apps	I-Application
,	O
access	O
browser	O
configuration	O
,	O
as	O
well	O
as	O
perform	O
a	O
search	O
.	O
</s>
<s>
Google	B-Application
,	O
which	O
has	O
been	O
called	O
"	O
the	O
command	B-Application
line	I-Application
of	O
the	O
internet	O
"	O
will	O
perform	O
a	O
domain-specific	O
search	O
when	O
it	O
detects	O
search	O
parameters	O
in	O
a	O
known	O
format	O
.	O
</s>
<s>
This	O
functionality	O
is	O
present	O
whether	O
the	O
search	O
is	O
triggered	O
from	O
a	O
browser	O
field	O
or	O
on	O
Google	B-Application
's	I-Application
website	O
.	O
</s>
<s>
There	O
are	O
JavaScript	B-Language
libraries	O
that	O
allow	O
to	O
write	O
command	B-Application
line	I-Application
applications	O
in	O
browser	O
as	O
standalone	O
Web	B-Application
apps	I-Application
or	O
as	O
part	O
of	O
bigger	O
application	O
.	O
</s>
<s>
An	O
example	O
of	O
such	O
a	O
website	O
is	O
the	O
CLI	O
interface	O
to	O
DuckDuckGo	B-Application
.	O
</s>
<s>
There	O
are	O
also	O
Web-based	B-Protocol
SSH	I-Protocol
applications	O
,	O
that	O
allow	O
to	O
give	O
access	O
to	O
server	O
command	B-Application
line	I-Application
interface	I-Application
from	O
a	O
browser	O
.	O
</s>
<s>
Many	O
video	O
games	O
on	O
the	O
PC	O
feature	O
a	O
command	B-Application
line	I-Application
interface	I-Application
often	O
referred	O
to	O
as	O
a	O
console	O
.	O
</s>
