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A regular expression is a case-sensitive string of 1 to 256 characters. It supports the following special
characters.
Character Meanin
Remarks
^string
Starting sign. string appears only at
the beginning of a line.
For example, regular expression “^user” only
matches a string beginning with “user," not
“Auser."
string$
Ending sign. string appears only at
the end of a line.
For example, regular expression "user$” only
matches a string ending with “user," not “userA."
.
Matches any single character, such
as a single character, a special
character, and a blank.
For example, “.s” matches “as” and “bs."
*
Matches the preceding character or
character group zero or multiple
times.
For example, “zo*” matches “z” and “zoo”;
“(zo)*” matches “zo” and “zozo."
+
Matches the preceding character or
character group one or multiple
times
For example, “zo+” matches “zo” and “zoo," but
not “z."
|
Matches the preceding or
succeeding character string
For example, “def|int” only matches a character
string containing “def” or “int."
_
If it is at the beginning or the end of a
regular expression, it equals ^ or $.
In other cases, it equals comma,
space, round bracket, or curly
bracket.
For example, “a_b” matches “a b” or “a(b”; “_ab”
only matches a line starting with “ab”; “ab_” only
matches a line ending with “ab."
-
It connects two values (the smaller
one before it and the bigger one
after it) to indicate a range together
with [ ].
For example, “1-9” means 1 to 9 (inclusive); “a-h”
means a to h (inclusive).
[ ]
Matches a single character
contained within the brackets.
For example, [16A] matches a string containing
any character among 1, 6, and A; [1-36A] matches
a string containing any character among 1, 2, 3, 6,
and A (- is a hyphen).
“]” can be matched as a common character only
when it is put at the beginning of characters within
the brackets, for example [ ]string]. There is no such
limit on “[."
()
A character group. It is usually used
with “+” or “*."
For example, (123A) means a character group
“123A”; “408(12)+” matches 40812 or
408121212. But it does not match 408.
\index
Repeats the character string
specified by the index. A character
string refers to the string within ()
before \. index refers to the
sequence number (starting from 1
from left to right) of the character
group before \. If only one character
group appears before \, index can
only be 1; if n character groups
appear before index, index can be
any integer from 1 to n.
For example, (string)\1 repeats string, and a
matching string must contain stringstring.
(string1)(string2)\2 repeats string2, and a
matching string must contain string1string2string2.
(string1)(string2)\1\2 repeats string1 and string2
respectively, and a matching string must contain
string1string2string1string2.
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