<s>
A	O
shell	B-Language
script	I-Language
is	O
a	O
computer	B-Application
program	I-Application
designed	O
to	O
be	O
run	O
by	O
a	O
Unix	B-Application
shell	I-Application
,	O
a	O
command-line	O
interpreter	O
.	O
</s>
<s>
The	O
various	O
dialects	O
of	O
shell	B-Language
scripts	I-Language
are	O
considered	O
to	O
be	O
scripting	B-Language
languages	I-Language
.	O
</s>
<s>
Typical	O
operations	O
performed	O
by	O
shell	B-Language
scripts	I-Language
include	O
file	O
manipulation	O
,	O
program	O
execution	O
,	O
and	O
printing	O
text	O
.	O
</s>
<s>
The	O
term	O
is	O
also	O
used	O
more	O
generally	O
to	O
mean	O
the	O
automated	O
mode	O
of	O
running	O
an	O
operating	O
system	O
shell	O
;	O
each	O
operating	O
system	O
uses	O
a	O
particular	O
name	O
for	O
these	O
functions	O
including	O
batch	O
files	O
(	O
MSDos-Win95	O
stream	O
,	O
OS/2	B-Application
)	O
,	O
command	O
procedures	O
(	O
VMS	O
)	O
,	O
and	O
shell	B-Language
scripts	I-Language
(	O
Windows	B-Device
NT	I-Device
stream	O
and	O
third-party	O
derivatives	O
like	O
4NT	B-Application
—	O
article	O
is	O
at	O
cmd.exe	B-Device
)	O
,	O
and	O
mainframe	O
operating	O
systems	O
are	O
associated	O
with	O
a	O
number	O
of	O
terms	O
.	O
</s>
<s>
Shells	O
commonly	O
present	O
in	O
Unix	O
and	O
Unix-like	O
systems	O
include	O
the	O
Korn	B-Language
shell	I-Language
,	O
the	B-Device
Bourne	I-Device
shell	I-Device
,	O
and	O
GNU	B-Operating_System
Bash	I-Operating_System
.	O
</s>
<s>
While	O
a	O
Unix	O
operating	O
system	O
may	O
have	O
a	O
different	O
default	O
shell	O
,	O
such	O
as	O
Zsh	B-Application
on	O
macOS	B-Application
,	O
these	O
shells	O
are	O
typically	O
present	O
for	O
backwards	O
compatibility	O
.	O
</s>
<s>
The	O
shebang	B-Operating_System
,	O
or	O
hash-bang	B-Operating_System
,	O
is	O
a	O
special	O
kind	O
of	O
comment	O
which	O
the	O
system	O
uses	O
to	O
determine	O
what	O
interpreter	O
to	O
use	O
to	O
execute	O
the	O
file	O
.	O
</s>
<s>
The	O
shebang	B-Operating_System
must	O
be	O
the	O
first	O
line	O
of	O
the	O
file	O
,	O
and	O
start	O
with	O
"	O
#	O
!	O
"	O
.	O
</s>
<s>
A	O
shell	B-Language
script	I-Language
can	O
provide	O
a	O
convenient	O
variation	O
of	O
a	O
system	O
command	O
where	O
special	O
environment	O
settings	O
,	O
command	O
options	O
,	O
or	O
post-processing	O
apply	O
automatically	O
,	O
but	O
in	O
a	O
way	O
that	O
allows	O
the	O
new	O
script	O
to	O
still	O
act	O
as	O
a	O
fully	O
normal	O
Unix	B-Application
command	I-Application
.	O
</s>
<s>
One	O
example	O
would	O
be	O
to	O
create	O
a	O
version	O
of	O
ls	B-Application
,	O
the	O
command	O
to	O
list	O
files	O
,	O
giving	O
it	O
a	O
shorter	O
command	O
name	O
of	O
l	O
,	O
which	O
would	O
be	O
normally	O
saved	O
in	O
a	O
user	O
's	O
bin	O
directory	O
as	O
/home/username/bin/l	O
,	O
and	O
a	O
default	O
set	O
of	O
command	O
options	O
pre-supplied	O
.	O
</s>
<s>
Here	O
,	O
the	O
first	O
line	O
uses	O
a	O
shebang	B-Operating_System
to	O
indicate	O
which	O
interpreter	O
should	O
execute	O
the	O
rest	O
of	O
the	O
script	O
,	O
and	O
the	O
second	O
line	O
makes	O
a	O
listing	O
with	O
options	O
for	O
file	O
format	O
indicators	O
,	O
columns	O
,	O
all	O
files	O
(	O
none	O
omitted	O
)	O
,	O
and	O
a	O
size	O
in	O
blocks	O
.	O
</s>
<s>
The	O
LC_COLLATE	O
=	O
C	B-Language
sets	O
the	O
default	O
collation	O
order	O
to	O
not	O
fold	O
upper	O
and	O
lower	O
case	O
together	O
,	O
not	O
intermix	O
dotfiles	O
with	O
normal	O
filenames	O
as	O
a	O
side	O
effect	O
of	O
ignoring	O
punctuation	O
in	O
the	O
names	O
(	O
dotfiles	O
are	O
usually	O
only	O
shown	O
if	O
an	O
option	O
like	O
-a	O
is	O
used	O
)	O
,	O
and	O
the	O
"	O
$@	O
"	O
causes	O
any	O
parameters	O
given	O
to	O
l	O
to	O
pass	O
through	O
as	O
parameters	O
to	O
ls	B-Application
,	O
so	O
that	O
all	O
of	O
the	O
normal	O
options	O
and	O
other	O
syntax	O
known	O
to	O
ls	B-Application
can	O
still	O
be	O
used	O
.	O
</s>
<s>
Another	O
example	O
of	O
a	O
shell	B-Language
script	I-Language
that	O
could	O
be	O
used	O
as	O
a	O
shortcut	O
would	O
be	O
to	O
print	O
a	O
list	O
of	O
all	O
the	O
files	O
and	O
directories	O
within	O
a	O
given	O
directory	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
shell	B-Language
script	I-Language
would	O
start	O
with	O
its	O
normal	O
starting	O
line	O
of	O
#	O
!	O
/bin/sh	B-Device
.	O
</s>
<s>
The	O
ls	B-Application
-al	O
command	O
lists	O
the	O
files	O
and	O
directories	O
that	O
are	O
in	O
the	O
directory	O
from	O
which	O
the	O
script	O
is	O
being	O
run	O
.	O
</s>
<s>
The	O
ls	B-Application
command	O
attributes	O
could	O
be	O
changed	O
to	O
reflect	O
the	O
needs	O
of	O
the	O
user	O
.	O
</s>
<s>
Shell	B-Language
scripts	I-Language
allow	O
several	O
commands	O
that	O
would	O
be	O
entered	O
manually	O
at	O
a	O
command-line	O
interface	O
to	O
be	O
executed	O
automatically	O
,	O
and	O
without	O
having	O
to	O
wait	O
for	O
a	O
user	O
to	O
trigger	O
each	O
stage	O
of	O
the	O
sequence	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
directory	O
with	O
three	O
C	B-Language
source	O
code	O
files	O
,	O
rather	O
than	O
manually	O
running	O
the	O
four	O
commands	O
required	O
to	O
build	O
the	O
final	O
program	O
from	O
them	O
,	O
one	O
could	O
instead	O
create	O
a	O
script	O
for	O
POSIX-compliant	O
shells	O
,	O
here	O
named	O
build	O
and	O
kept	O
in	O
the	O
directory	O
with	O
them	O
,	O
which	O
would	O
compile	O
them	O
automatically	O
:	O
</s>
<s>
Since	O
the	O
1980s	O
or	O
so	O
,	O
however	O
,	O
scripts	O
of	O
this	O
type	O
have	O
been	O
replaced	O
with	O
utilities	O
like	O
make	B-Application
which	O
are	O
specialized	O
for	O
building	O
programs	O
.	O
</s>
<s>
Many	O
modern	O
shells	O
also	O
supply	O
various	O
features	O
usually	O
found	O
only	O
in	O
more	O
sophisticated	O
general-purpose	B-Language
programming	I-Language
languages	I-Language
,	O
such	O
as	O
control-flow	O
constructs	O
,	O
variables	O
,	O
comments	O
,	O
arrays	O
,	O
subroutines	O
and	O
so	O
on	O
.	O
</s>
<s>
With	O
these	O
sorts	O
of	O
features	O
available	O
,	O
it	O
is	O
possible	O
to	O
write	O
reasonably	O
sophisticated	O
applications	O
as	O
shell	B-Language
scripts	I-Language
.	O
</s>
<s>
However	O
,	O
they	O
are	O
still	O
limited	O
by	O
the	O
fact	O
that	O
most	O
shell	B-Language
languages	I-Language
have	O
little	O
or	O
no	O
support	O
for	O
data	O
typing	O
systems	O
,	O
classes	O
,	O
threading	O
,	O
complex	O
math	O
,	O
and	O
other	O
common	O
full	O
language	O
features	O
,	O
and	O
are	O
also	O
generally	O
much	O
slower	O
than	O
compiled	O
code	O
or	O
interpreted	O
languages	O
written	O
with	O
speed	O
as	O
a	O
performance	O
goal	O
.	O
</s>
<s>
The	O
standard	O
Unix	B-Application
tools	I-Application
sed	B-Application
and	O
awk	B-Application
provide	O
extra	O
capabilities	O
for	O
shell	O
programming	O
;	O
Perl	B-Language
can	O
also	O
be	O
embedded	O
in	O
shell	B-Language
scripts	I-Language
as	O
can	O
other	O
scripting	B-Language
languages	I-Language
like	O
Tcl	B-Operating_System
.	O
</s>
<s>
Perl	B-Language
and	O
Tcl	B-Operating_System
come	O
with	O
graphics	O
toolkits	O
as	O
well	O
.	O
</s>
<s>
Scripting	B-Language
languages	I-Language
commonly	O
found	O
on	O
UNIX	O
,	O
Linux	O
,	O
and	O
POSIX-compliant	O
operating	O
system	O
installations	O
include	O
:	O
</s>
<s>
KornShell	B-Language
(	O
ksh	O
)	O
in	O
several	O
possible	O
versions	O
such	O
as	O
ksh88	B-Language
,	O
Korn	B-Language
Shell	I-Language
'	O
93	O
and	O
others	O
.	O
</s>
<s>
tclsh	O
,	O
a	O
shell	O
which	O
is	O
a	O
main	O
component	O
of	O
the	O
Tcl/Tk	B-Operating_System
programming	O
language	O
.	O
</s>
<s>
The	O
wish	B-Application
is	O
a	O
GUI-based	O
Tcl/Tk	B-Operating_System
shell	O
.	O
</s>
<s>
The	O
C	B-Language
and	O
Tcl	B-Operating_System
shells	O
have	O
syntax	O
quite	O
similar	O
to	O
that	O
of	O
said	O
programming	O
languages	O
,	O
and	O
the	O
Korn	B-Language
shells	I-Language
and	O
Bash	B-Operating_System
are	O
developments	O
of	O
the	B-Device
Bourne	I-Device
shell	I-Device
,	O
which	O
is	O
based	O
on	O
the	O
ALGOL	B-Language
language	I-Language
with	O
elements	O
of	O
a	O
number	O
of	O
others	O
added	O
as	O
well	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
the	O
various	O
shells	O
plus	O
tools	O
like	O
awk	B-Application
,	O
sed	B-Application
,	O
grep	B-Application
,	O
and	O
BASIC	O
,	O
Lisp	B-Language
,	O
C	B-Language
and	O
so	O
forth	O
contributed	O
to	O
the	O
Perl	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
The	O
Tenex	B-Language
C	I-Language
Shell	I-Language
(	O
tcsh	B-Language
)	O
.	O
</s>
<s>
Related	O
programs	O
such	O
as	O
shells	O
based	O
on	O
Python	B-Language
,	O
Ruby	B-Language
,	O
C	B-Language
,	O
Java	B-Language
,	O
Perl	B-Language
,	O
Pascal	B-Application
,	O
Rexx	B-Language
etc	O
.	O
</s>
<s>
Many	O
powerful	O
scripting	B-Language
languages	I-Language
have	O
been	O
introduced	O
for	O
tasks	O
that	O
are	O
too	O
large	O
or	O
complex	O
to	O
be	O
comfortably	O
handled	O
with	O
ordinary	O
shell	B-Language
scripts	I-Language
,	O
but	O
for	O
which	O
the	O
advantages	O
of	O
a	O
script	O
are	O
desirable	O
and	O
the	O
development	O
overhead	O
of	O
a	O
full-blown	O
,	O
compiled	O
programming	O
language	O
would	O
be	O
disadvantageous	O
.	O
</s>
<s>
The	O
specifics	O
of	O
what	O
separates	O
scripting	B-Language
languages	I-Language
from	O
high-level	B-Language
programming	I-Language
languages	I-Language
is	O
a	O
frequent	O
source	O
of	O
debate	O
,	O
but	O
,	O
generally	O
speaking	O
,	O
a	O
scripting	B-Language
language	I-Language
is	O
one	O
which	O
requires	O
an	O
interpreter	O
.	O
</s>
<s>
Shell	B-Language
scripts	I-Language
often	O
serve	O
as	O
an	O
initial	O
stage	O
in	O
software	O
development	O
,	O
and	O
are	O
often	O
subject	O
to	O
conversion	O
later	O
to	O
a	O
different	O
underlying	O
implementation	O
,	O
most	O
commonly	O
being	O
converted	O
to	O
Perl	B-Language
,	O
Python	B-Language
,	O
or	O
C	B-Language
.	O
The	O
interpreter	B-Operating_System
directive	I-Operating_System
allows	O
the	O
implementation	O
detail	O
to	O
be	O
fully	O
hidden	O
inside	O
the	O
script	O
,	O
rather	O
than	O
being	O
exposed	O
as	O
a	O
filename	O
extension	O
,	O
and	O
provides	O
for	O
seamless	O
reimplementation	O
in	O
different	O
languages	O
with	O
no	O
impact	O
on	O
end	O
users	O
.	O
</s>
<s>
While	O
files	O
with	O
the	O
"	O
.sh	O
"	O
file	O
extension	O
are	O
usually	O
a	O
shell	B-Language
script	I-Language
of	O
some	O
kind	O
,	O
most	O
shell	B-Language
scripts	I-Language
do	O
not	O
have	O
any	O
filename	O
extension	O
.	O
</s>
<s>
Perhaps	O
the	O
biggest	O
advantage	O
of	O
writing	O
a	O
shell	B-Language
script	I-Language
is	O
that	O
the	O
commands	O
and	O
syntax	O
are	O
exactly	O
the	O
same	O
as	O
those	O
directly	O
entered	O
at	O
the	O
command-line	O
.	O
</s>
<s>
Often	O
,	O
writing	O
a	O
shell	B-Language
script	I-Language
is	O
much	O
quicker	O
than	O
writing	O
the	O
equivalent	O
code	O
in	O
other	O
programming	O
languages	O
.	O
</s>
<s>
A	O
shell	B-Language
script	I-Language
can	O
be	O
used	O
to	O
provide	O
a	O
sequencing	O
and	O
decision-making	O
linkage	O
around	O
existing	O
programs	O
,	O
and	O
for	O
moderately	O
sized	O
scripts	O
the	O
absence	O
of	O
a	O
compilation	O
step	O
is	O
an	O
advantage	O
.	O
</s>
<s>
Non-expert	O
users	O
can	O
use	O
scripting	O
to	O
tailor	O
the	O
behavior	O
of	O
programs	O
,	O
and	O
shell	B-Language
scripting	I-Language
provides	O
some	O
limited	O
scope	O
for	O
multiprocessing	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
shell	B-Language
scripting	I-Language
is	O
prone	O
to	O
costly	O
errors	O
.	O
</s>
<s>
Inadvertent	O
typing	O
errors	O
such	O
as	O
rm	B-Application
-rf	I-Application
*	I-Application
/	O
(	O
instead	O
of	O
the	O
intended	O
rm	B-Application
-rf	I-Application
*	I-Application
/	O
)	O
are	O
folklore	O
in	O
the	O
Unix	O
community	O
;	O
a	O
single	O
extra	O
space	O
converts	O
the	O
command	O
from	O
one	O
that	O
deletes	O
all	O
subdirectories	O
contained	O
in	O
the	O
current	O
directory	O
,	O
to	O
one	O
which	O
deletes	O
everything	O
from	O
the	O
file	O
system	O
's	O
root	B-Application
directory	I-Application
.	O
</s>
<s>
Similar	O
problems	O
can	O
transform	O
cp	B-Application
and	O
mv	O
into	O
dangerous	O
weapons	O
,	O
and	O
misuse	O
of	O
the	O
>	O
redirect	O
can	O
delete	O
the	O
contents	O
of	O
a	O
file	O
.	O
</s>
<s>
This	O
is	O
made	O
more	O
problematic	O
by	O
the	O
fact	O
that	O
many	O
UNIX	B-Application
commands	I-Application
differ	O
in	O
name	O
by	O
only	O
one	O
letter	O
:	O
cp	B-Application
,	O
cd	B-Application
,	O
dd	B-Application
,	O
df	B-Device
,	O
etc	O
.	O
</s>
<s>
When	O
a	O
script	O
's	O
job	O
can	O
be	O
accomplished	O
by	O
setting	O
up	O
a	O
pipeline	B-General_Concept
in	O
which	O
efficient	O
filter	B-Application
commands	O
perform	O
most	O
of	O
the	O
work	O
,	O
the	O
slowdown	O
is	O
mitigated	O
,	O
but	O
a	O
complex	O
script	O
is	O
typically	O
several	O
orders	O
of	O
magnitude	O
slower	O
than	O
a	O
conventional	O
compiled	O
program	O
that	O
performs	O
an	O
equivalent	O
task	O
.	O
</s>
<s>
Larry	O
Wall	O
,	O
creator	O
of	O
Perl	B-Language
,	O
famously	O
wrote	O
that	O
"	O
It	O
is	O
easier	O
to	O
port	O
a	O
shell	O
than	O
a	O
shell	O
script.	O
"	O
</s>
<s>
Similarly	O
,	O
more	O
complex	O
scripts	O
can	O
run	O
into	O
the	O
limitations	O
of	O
the	O
shell	B-Language
scripting	I-Language
language	O
itself	O
;	O
the	O
limits	O
make	B-Application
it	O
difficult	O
to	O
write	O
quality	O
code	O
,	O
and	O
extensions	O
by	O
various	O
shells	O
to	O
ameliorate	O
problems	O
with	O
the	O
original	O
shell	B-Language
language	I-Language
can	O
make	B-Application
problems	O
worse	O
.	O
</s>
<s>
Many	O
disadvantages	O
of	O
using	O
some	O
script	B-Language
languages	I-Language
are	O
caused	O
by	O
design	O
flaws	O
within	O
the	O
language	O
syntax	O
or	O
implementation	O
,	O
and	O
are	O
not	O
necessarily	O
imposed	O
by	O
the	O
use	O
of	O
a	O
text-based	O
command-line	O
;	O
there	O
are	O
a	O
number	O
of	O
shells	O
which	O
use	O
other	O
shell	O
programming	O
languages	O
or	O
even	O
full-fledged	O
languages	O
like	O
Scsh	B-Language
(	O
which	O
uses	O
Scheme	B-Language
)	O
.	O
</s>
<s>
Different	O
scripting	B-Language
languages	I-Language
may	O
share	O
many	O
common	O
elements	O
,	O
largely	O
due	O
to	O
being	O
POSIX	O
based	O
,	O
and	O
some	O
shells	O
offer	O
modes	O
to	O
emulate	O
different	O
shells	O
.	O
</s>
<s>
This	O
allows	O
a	O
shell	B-Language
script	I-Language
written	O
in	O
one	O
scripting	B-Language
language	I-Language
to	O
be	O
adapted	O
into	O
another	O
.	O
</s>
<s>
One	O
example	O
of	O
this	O
is	O
Bash	B-Operating_System
,	O
which	O
offers	O
the	O
same	O
grammar	O
and	O
syntax	O
as	O
the	B-Device
Bourne	I-Device
shell	I-Device
,	O
and	O
which	O
also	O
provides	O
a	O
POSIX-compliant	O
mode	O
.	O
</s>
<s>
As	O
such	O
,	O
most	O
shell	B-Language
scripts	I-Language
written	O
for	O
the	B-Device
Bourne	I-Device
shell	I-Device
can	O
be	O
run	O
in	O
BASH	B-Operating_System
,	O
but	O
the	O
reverse	O
may	O
not	O
be	O
true	O
since	O
BASH	B-Operating_System
has	O
extensions	O
which	O
are	O
not	O
present	O
in	O
the	B-Device
Bourne	I-Device
shell	I-Device
.	O
</s>
<s>
Interoperability	O
software	O
such	O
as	O
Cygwin	B-Language
,	O
the	O
MKS	B-Application
Toolkit	I-Application
,	O
Interix	B-Operating_System
(	O
which	O
is	O
available	O
in	O
the	O
Microsoft	O
Windows	O
Services	O
for	O
UNIX	O
)	O
,	O
Hamilton	B-Device
C	I-Device
shell	I-Device
,	O
UWIN	B-Application
(	O
AT&T	O
Unix	O
for	O
Windows	O
)	O
and	O
others	O
allow	O
Unix	B-Application
shell	I-Application
programs	O
to	O
be	O
run	O
on	O
machines	O
running	O
Windows	B-Device
NT	I-Device
and	O
its	O
successors	O
,	O
with	O
some	O
loss	O
of	O
functionality	O
on	O
the	O
MS-DOS-Windows	O
95	O
branch	O
,	O
as	O
well	O
as	O
earlier	O
MKS	B-Application
Toolkit	I-Application
versions	O
for	O
OS/2	B-Application
.	O
</s>
<s>
At	O
least	O
three	O
DCL	O
implementations	O
for	O
Windows	O
type	O
operating	O
systems	O
—	O
in	O
addition	O
to	O
XLNT	B-Language
,	O
a	O
multiple-use	O
scripting	B-Language
language	I-Language
package	O
which	O
is	O
used	O
with	O
the	O
command	O
shell	O
,	O
Windows	O
Script	O
Host	O
and	O
CGI	B-Language
programming	O
—	O
are	O
available	O
for	O
these	O
systems	O
as	O
well	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	O
and	O
subsequent	O
are	O
Unix-like	O
as	O
well	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
aforementioned	O
tools	O
,	O
some	O
POSIX	O
and	O
OS/2	B-Application
functionality	O
can	O
be	O
used	O
with	O
the	O
corresponding	O
environmental	O
subsystems	O
of	O
the	O
Windows	B-Device
NT	I-Device
operating	O
system	O
series	O
up	O
to	O
Windows	O
2000	O
as	O
well	O
.	O
</s>
<s>
A	O
third	O
,	O
16-bit	B-Device
subsystem	O
often	O
called	O
the	O
MS-DOS	B-Application
subsystem	O
uses	O
the	O
Command.com	O
provided	O
with	O
these	O
operating	O
systems	O
to	O
run	O
the	O
aforementioned	O
MS-DOS	B-Application
batch	O
files	O
.	O
</s>
<s>
The	O
console	O
alternatives	O
4DOS	B-Application
,	O
4OS2	B-Application
,	O
FreeDOS	B-Application
,	O
Peter	O
Norton	O
's	O
NDOS	B-Application
and	O
4NT	B-Application
/	O
Take	B-Application
Command	I-Application
which	O
add	O
functionality	O
to	O
the	O
Windows	O
NT-style	O
cmd.exe	B-Device
,	O
MS-DOS/Windows	O
95	O
batch	O
files	O
(	O
run	O
by	O
Command.com	O
)	O
,	O
OS/2	B-Application
'	O
s	O
cmd.exe	B-Device
,	O
and	O
4NT	B-Application
respectively	O
are	O
similar	O
to	O
the	O
shells	O
that	O
they	O
enhance	O
and	O
are	O
more	O
integrated	O
with	O
the	O
Windows	O
Script	O
Host	O
,	O
which	O
comes	O
with	O
three	O
pre-installed	O
engines	O
,	O
VBScript	B-Application
,	O
JScript	B-Language
,	O
and	O
VBA	B-Language
and	O
to	O
which	O
numerous	O
third-party	O
engines	O
can	O
be	O
added	O
,	O
with	O
Rexx	B-Language
,	O
Perl	B-Language
,	O
Python	B-Language
,	O
Ruby	B-Language
,	O
and	O
Tcl	B-Operating_System
having	O
pre-defined	O
functions	O
in	O
4NT	B-Application
and	O
related	O
programs	O
.	O
</s>
<s>
PC	B-Operating_System
DOS	I-Operating_System
is	O
quite	O
similar	O
to	O
MS-DOS	B-Application
,	O
whilst	O
DR	B-Application
DOS	I-Application
is	O
more	O
different	O
.	O
</s>
<s>
Earlier	O
versions	O
of	O
Windows	B-Device
NT	I-Device
are	O
able	O
to	O
run	O
contemporary	O
versions	O
of	O
4OS2	B-Application
by	O
the	O
OS/2	B-Application
subsystem	O
.	O
</s>
<s>
Scripting	B-Language
languages	I-Language
are	O
,	O
by	O
definition	O
,	O
able	O
to	O
be	O
extended	O
;	O
for	O
example	O
,	O
a	O
MS-DOS/Windows	O
95/98	O
and	O
Windows	B-Device
NT	I-Device
type	O
systems	O
allows	O
for	O
shell/batch	O
programs	O
to	O
call	O
tools	O
like	O
KiXtart	B-Language
,	O
QBasic	B-Language
,	O
various	O
BASIC	O
,	O
Rexx	B-Language
,	O
Perl	B-Language
,	O
and	O
Python	B-Language
implementations	O
,	O
the	O
Windows	O
Script	O
Host	O
and	O
its	O
installed	O
engines	O
.	O
</s>
<s>
On	O
Unix	O
and	O
other	O
POSIX-compliant	O
systems	O
,	O
awk	B-Application
and	O
sed	B-Application
are	O
used	O
to	O
extend	O
the	O
string	O
and	O
numeric	O
processing	O
ability	O
of	O
shell	B-Language
scripts	I-Language
.	O
</s>
<s>
Tcl	B-Operating_System
,	O
Perl	B-Language
,	O
Rexx	B-Language
,	O
and	O
Python	B-Language
have	O
graphics	O
toolkits	O
and	O
can	O
be	O
used	O
to	O
code	O
functions	O
and	O
procedures	O
for	O
shell	B-Language
scripts	I-Language
which	O
pose	O
a	O
speed	O
bottleneck	O
(	O
C	B-Language
,	O
Fortran	O
,	O
assembly	O
language	O
&	O
c	B-Language
are	O
much	O
faster	O
still	O
)	O
and	O
to	O
add	O
functionality	O
not	O
available	O
in	O
the	O
shell	B-Language
language	I-Language
such	O
as	O
sockets	O
and	O
other	O
connectivity	O
functions	O
,	O
heavy-duty	O
text	O
processing	O
,	O
working	O
with	O
numbers	O
if	O
the	O
calling	O
script	O
does	O
not	O
have	O
those	O
abilities	O
,	O
self-writing	O
and	O
self-modifying	O
code	O
,	O
techniques	O
like	O
recursion	O
,	O
direct	O
memory	O
access	O
,	O
various	O
types	O
of	O
sorting	B-Algorithm
and	O
more	O
,	O
which	O
are	O
difficult	O
or	O
impossible	O
in	O
the	O
main	O
script	O
,	O
and	O
so	O
on	O
.	O
</s>
<s>
Visual	B-Language
Basic	I-Language
for	I-Language
Applications	I-Language
and	O
VBScript	B-Application
can	O
be	O
used	O
to	O
control	O
and	O
communicate	O
with	O
such	O
things	O
as	O
spreadsheets	O
,	O
databases	O
,	O
scriptable	O
programs	O
of	O
all	O
types	O
,	O
telecommunications	O
software	O
,	O
development	O
tools	O
,	O
graphics	O
tools	O
and	O
other	O
software	O
which	O
can	O
be	O
accessed	O
through	O
the	O
Component	B-Application
Object	I-Application
Model	I-Application
.	O
</s>
