<s>
A	O
metacharacter	B-Algorithm
is	O
a	O
character	O
that	O
has	O
a	O
special	O
meaning	O
to	O
a	O
computer	O
program	O
,	O
such	O
as	O
a	O
shell	O
interpreter	O
or	O
a	O
regular	O
expression	O
(	O
regex	O
)	O
engine	O
.	O
</s>
<s>
In	O
POSIX	O
extended	O
regular	O
expressions	O
,	O
there	O
are	O
14	O
metacharacters	B-Algorithm
that	O
must	O
be	O
escaped	O
(	O
preceded	O
by	O
a	O
backslash	O
(	O
\	O
)	O
)	O
in	O
order	O
to	O
drop	O
their	O
special	O
meaning	O
and	O
be	O
treated	O
literally	O
inside	O
an	O
expression	O
:	O
opening	O
and	O
closing	O
square	O
brackets	O
( [	O
and	O
]	O
)	O
;	O
backslash	O
(	O
\	O
)	O
;	O
caret	O
( ^	O
)	O
;	O
dollar	O
sign	O
( $	O
)	O
;	O
period/full	O
stop/dot	O
(	O
.	O
</s>
<s>
In	O
some	O
Unix	B-Application
shells	I-Application
the	O
semicolon	O
(";	O
"	O
)	O
is	O
a	O
statement	O
separator	O
.	O
</s>
<s>
In	O
XML	B-Protocol
and	O
HTML	B-Language
,	O
the	O
ampersand	O
("&"	O
)	O
introduces	O
an	O
HTML	B-General_Concept
entity	I-General_Concept
.	O
</s>
<s>
It	O
also	O
has	O
special	O
meaning	O
in	O
MS-DOS/Windows	O
Command	O
Prompt	O
.	O
</s>
<s>
In	O
some	O
Unix	B-Application
shells	I-Application
and	O
MS-DOS/Windows	O
Command	O
Prompt	O
,	O
the	O
less-than	O
sign	O
and	O
greater-than	O
sign	O
(	O
"	O
<" and ">	O
"	O
)	O
are	O
used	O
for	O
redirection	B-Device
and	O
the	O
backtick/grave	O
accent	O
("`"	O
)	O
is	O
used	O
for	O
command	B-Device
substitution	I-Device
.	O
</s>
<s>
In	O
many	O
programming	O
languages	O
,	O
strings	O
are	O
delimited	B-Algorithm
using	O
quotes	O
(	O
"	O
or	O
'	O
)	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
escape	B-Algorithm
characters	I-Algorithm
(	O
and	O
other	O
methods	O
)	O
are	O
used	O
to	O
avoid	O
delimiter	B-Algorithm
collision	O
,	O
e.g.	O
</s>
<s>
In	O
printf	B-Language
format	I-Language
strings	I-Language
,	O
the	O
percent	O
sign	O
("%"	O
)	O
is	O
used	O
to	O
introduce	O
format	B-Language
specifiers	I-Language
and	O
must	O
be	O
escaped	O
as	O
"	O
%%	O
"	O
to	O
be	O
interpreted	O
literally	O
.	O
</s>
<s>
In	O
SQL	B-Language
,	O
the	O
percent	O
is	O
used	O
as	O
a	O
wildcard	B-Algorithm
character	I-Algorithm
.	O
</s>
<s>
In	O
SQL	B-Language
,	O
the	O
underscore	O
("_"	O
)	O
is	O
used	O
to	O
match	O
any	O
single	O
character	O
.	O
</s>
<s>
The	O
term	O
"	O
to	O
escape	O
a	O
metacharacter	B-Algorithm
"	O
means	O
to	O
make	O
the	O
metacharacter	B-Algorithm
ineffective	O
(	O
to	O
strip	O
it	O
of	O
its	O
special	O
meaning	O
)	O
,	O
causing	O
it	O
to	O
have	O
its	O
literal	O
meaning	O
.	O
</s>
<s>
is	O
escaped	O
,	O
it	O
will	O
lose	O
its	O
meaning	O
as	O
a	O
metacharacter	B-Algorithm
and	O
will	O
be	O
interpreted	O
literally	O
as	O
"	O
.	O
</s>
<s>
Other	O
environments	O
may	O
employ	O
different	O
methods	O
,	O
like	O
MS-DOS/Windows	O
Command	O
Prompt	O
,	O
where	O
a	O
caret	O
("^"	O
)	O
is	O
used	O
instead	O
.	O
</s>
