Perl正则表达式

Metacharacters

To present a metacharacter as a data character standing for itself,precede it with??(e.g.?.?matches the full stop character?.?only).

Repetition

Read the notation?a’s as “occurrences of strings,each of which matches the pattern?”. Read?repetition?as any of the repetition expressions listed above it. Shortest match means that the shortest string matching the pattern is taken. The default is?“greedy matching”,which finds the longest match. Therepetition??construct was introduced in Perl version?5.

Calling these "wildcards" may actually conflict with the theoretical grammar and syntax of Perl,but in fact is the most intuitive way to think of it,and will not lead to any coding mistakes.

.???Match?any?character
w??Match?"word"?character?(alphanumeric?plus?"_")
W??Match?non-word?character
s??Match?whitespace?character
S??Match?non-whitespace?character
d??Match?digit?character
D??Match?non-digit?character
t??Match?tab
n??Match?newline
r??Match?return
f??Match?formfeed
a??Match?alarm?(bell,?beep,?etc)
e??Match?escape
21??Match?octal?char?(?in?this?case?21?octal)
xf0??Match?hex?char?(?in?this?case?f0?hexidecimal)

You can follow any character,wildcard,or series of characters and/or wildcard with a repetiton. Here's where you start getting some power:

*??????Match?0?or?more?times
+??????Match?1?or?more?times
???????Match?1?or?0?times
{n}????Match?exactly?n?times
{n,}???Match?at?least?n?times
{n,m}??Match?at?least?n?but?not?more?than?m?times

Code????????????????Meaning
----------??????????--------------------------------------------
w??????????????????Alphanumeric?Characters
W??????????????????Non-Alphanumeric?Characters
s??????????????????White?Space
S??????????????????Non-White?Space
d??????????????????Digits
D??????????????????Non-Digits?
b??????????????????Word?Boundary
B??????????????????Non-Word?Boundary
A?or?^?????????????At?the?beginning?of?a?string
Z?or?$?????????????At?the?end?of?a?string
.???????????????????Match?Any?single?character
*???????????????????Zero?or?more?occurrences
????????????????????Zero?or?one?Occurences
+???????????????????one?or?more?occurences
{N}?????????????????Exactly?N?occurences
{N,M}???????????????Between?N?and?M?occurences
.*<thingy>??????????Greedy?Match,?up?to?the?last?thingy
.*?<thingy>?????????Non-Greedy?match,?up?to?the?first?thingy
[set_of_things]?????Match?any?item?in?the?set
[^set_of_things]????Does?not?match?anything?in?the?set
(some_expression)???Tag?an?expression
$1..$N??????????????Tagged?expressions?used?in?substitutions