! i r1 W: U, B5 ~, {2 M每一个表达式都包含需要查找的指令,如表A所示。 / a2 [; K9 B" M0 C' A# w9 ^4 g0 ^6 e; h7 i4 R1 c2 R* _
Table A: Character-matching regular expressions / U. z+ k8 f/ c# N格式说明: 8 T/ ?7 x& x3 O8 ~) G# i--------------- " H. V0 _& b2 o5 s: d1 y
操作: 1 z1 H4 w i0 B0 N$ g: S% @! S解释: 6 @8 c& w; m( Q$ n3 P% z5 v例子: 9 w2 m8 R: B F; U结果: 7 }% P s) k. C---------------- $ z4 r0 s ?2 a* A1 _! v. - H$ m- \" N. H% U6 e3 F5 nMatch any one character; j$ m. Y6 ~8 q. m# y! X5 n
grep .ord sample.txt 6 [4 @/ K& h: w9 Q7 jWill match “ford”, “lord”, “2ord”, etc. in the file sample.txt. 9 t I+ C7 ]% R' y3 v( F* Y3 |- i----------------- $ p! Y, y$ x0 D9 a/ g6 F1 m
[ ]7 p- N' R" K. g0 C6 B" r# ?
Match any one character listed between the brackets+ |6 V" b* Y; P* ^4 ]
grep [cng]ord sample.txt 1 `5 @# V! X w8 _4 d! bWill match only “cord”, “nord”, and “gord” 5 T V+ g* p! \+ ?" {7 n--------------------- 9 o9 T. V& ?9 w7 r, H[^ ]/ M6 N: A! K% A- t* j( C) a2 P
Match any one character not listed between the brackets ; G0 A, i, g% y( A( s; h: f 2 P0 q$ S* b; g& W* U3 ]grep [^cn]ord sample.txt! t$ |( e! X- J6 T" L
Will match “lord”, “2ord”, etc. but not “cord” or “nord” + I) z. z* \1 y2 O. E# l& A( p6 q6 \1 m+ l
grep [a-zA-Z]ord sample.txt5 V+ |: Q' w- T# A# W
Will match “aord”, “bord”, “Aord”, “Bord”, etc.3 ~: j' z6 P" y
, I8 y" x. g/ L1 q z- rgrep [^0-9]ord sample.txt 1 u- F. k$ n0 O* uWill match “Aord”, “aord”, etc. but not “2ord”, etc. 1 q: h5 \1 x6 p" c, w" I( L7 \) |. M+ d2 [% z
重复操作符6 t/ p7 R9 G3 V
重复操作符,或数量词,都描述了查找一个特定字符的次数。它们常被用于字符匹配语法以查找多行的字符,可参见表B。 # O) {. ]2 p8 O) u- {9 J" q# a+ O; x
Table B: Regular expression repetition operators+ x. s" u! Q& p2 ^0 l" v
格式说明: / J5 Q; K6 ~2 E) e$ v--------------- 8 b7 A, p; A* W7 P: M# [( b1 J
操作:' M, ^$ \, ?8 @- Q# R; i2 W
解释:3 ]2 s' U: \+ s, t
例子: ) K# Q% R4 f+ l! x7 h/ B结果:$ g6 h9 ^+ ?2 o! m, l" E; l; {
---------------- ! E6 j* U: Q y* z9 @5 v8 g? 6 E2 D, m% H0 M, Z3 _( a$ {5 }Match any character one time, if it exists 2 m- k* W' p9 \8 J7 A+ |( v- Degrep “?erd” sample.txt 8 E& C7 d8 ^! x& F2 ZWill match “berd”, “herd”, etc. and “erd” % D4 K; H2 c! [- a# K* L% F7 D------------------ 8 |) x/ {5 j' }: `* B* 8 i7 _( n3 [& Z9 Q+ A% vMatch declared element multiple times, if it exists& N* k; |- d/ l0 `- @5 ^ A
egrep “n.*rd” sample.txt " {! g6 d+ ^! o4 y; CWill match “nerd”, “nrd”, “neard”, etc.. q, W% @2 b0 d9 E7 O
------------------- # j \ ]3 ~' b9 a) ]. V. w O+ 0 P+ \$ l- P; k$ _6 P4 U- z' L. F+ e0 TMatch declared element one or more times2 }; P5 q. J5 H) d5 i
egrep “[n]+erd” sample.txt * z) N# r) R/ ^Will match “nerd”, “nnerd”, etc., but not “erd”# F; d$ A3 Z# \5 S7 ?$ p
-------------------- & b4 L0 E3 v. v! N j# [* e( ?
{n} ) t0 h! B% p0 U4 gMatch declared element exactly n times$ s3 T: {. E8 ] L
egrep “[a-z]{2}erd” sample.txt7 {" N# g/ h0 F% q
Will match “cherd”, “blerd”, etc. but not “nerd”, “erd”, “buzzerd”, etc. c, a+ G0 i! K8 q* _& H
------------------------ 7 `* g# ]# S+ p
{n,}: Y: ?6 w# G' w! x% O, e
Match declared element at least n times , H( r- O+ ] F) p3 O. W( w v! ?1 Degrep “.{2,}erd” sample.txt- w5 C" D# y2 W) T7 t, t, B' |* H
Will match “cherd” and “buzzerd”, but not “nerd”0 s2 {* ^. p+ J# j: ~4 r5 W
------------------------ 1 v2 S7 r8 I3 f
{n,N} 3 E3 \- o- I0 @# B4 ]7 N% H( F5 \Match declared element at least n times, but not more than N times ( Y3 J2 m- H( f4 C5 a2 w# S! [egrep “n[e]{1,2}rd” sample.txt+ |* m4 G; i$ o$ a( L0 S6 A. z
Will match “nerd” and “neerd” / K# s& k& ?$ I + |! f' n9 q$ ^4 N* m4 v1 |第三部分: & f S: a; @3 W----------------5 t; P* n3 Z9 L F5 W( B
锚 2 G ~5 G# T# h$ o9 H0 U6 f. r锚是指它所要匹配的格式,如图C所示。使用它能方便你查找通用字符的合并。例如,我用vi行编辑器命令:s来代表substitute,这一命令的基本语法是: * Y. [) y* C( k% b1 z0 r4 t% L" r7 ~1 R( e3 V# s$ Y L
s/pattern_to_match/pattern_to_substitute/$ N. {4 B4 _# |2 n* @
. @1 ]9 O' R+ p. F 6 F" v( n6 C0 O* L2 H5 x3 I/ JTable C: Regular expression anchors + w7 i; w9 b& A2 n& p, t( h+ Q-------------0 j9 {1 K( u6 x0 @, ?; D
操作 6 ~ `) s3 u5 D解释 5 e' U& z* j- G' U* j例子- ^! a, M$ {; T4 G5 Y5 i
结果 7 f% W( E3 ]+ B4 T. z: b9 h4 E--------------- 4 m% D4 |1 i$ c% ^, m, k# K \
^9 K: I5 [0 G0 D7 i. j% e2 q2 l# G
Match at the beginning of a line& U* f# e1 S t6 [* v* x" A
s/^/blah /5 u* }" w1 W. h7 [
Inserts “blah “ at the beginning of the line 9 f; Y. n! A: |2 m1 ~6 W& s" F--------------- ' |8 w0 h1 ` p" v- [/ h7 C
$6 }* F W2 o% e2 v
Match at the end of a line6 t- }( T9 [+ ?
s/$/ blah/0 B6 F' t9 K% s$ W5 A; Z
Inserts “ blah” at the end of the line " x+ P) G/ X' T; Z( z- f' R7 `--------------- / f- [1 [, W u+ U% N0 Z8 o+ r2 X\< 2 I+ h8 D& F0 R$ W' CMatch at the beginning of a word# k; D5 x& |0 b1 C+ I/ q( W
s/\Inserts “blah” at the beginning of the word7 |- J* {4 u1 n+ U' a* s
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egrep “\Matches “blahfield”, etc.( @9 w( V4 e. r% M& l, @
------------------ ( R6 H4 L' {; K+ z/ Y6 E: q\>9 s, r4 e5 e) L! Y
Match at the end of a word4 U4 l: t* j w9 h/ [' @0 A4 l
s/\>/blah/ - B6 k$ G# P$ S3 H8 B5 hInserts “blah” at the end of the word ( X& h' g4 h- r; H; _3 g( J3 v# Q# T; W # g+ ~) Q3 v+ r+ p9 j7 Segrep “\>blah” sample.txt ) U0 v9 C- a8 }' y7 J; s hMatches “soupblah”, etc. & S. v+ K v v1 |2 P2 a---------------& y: W: m; v4 |" W3 E% W' Y5 L
\b - P8 V# q7 Q/ f2 FMatch at the beginning or end of a word 9 ^; ~+ q, X$ @' d3 w9 q8 Pegrep “\bblah” sample.txt ' g b7 a1 Q( [+ R& F, B8 T- hMatches “blahcake” and “countblah”* V1 y& q) O% t
----------------- 4 V0 S% Z |7 K! Q2 K" w\B* h( l6 a/ _- p ^& j( K' {
Match in the middle of a word$ Y( U6 Q; Z5 S( C4 w
egrep “\Bblah” sample.txt4 H: ?1 J/ {3 }0 I6 b* {! u1 E
Matches “sublahper”, etc." N/ n5 g0 M7 n; s# i
/ K% x$ @2 @: n6 X }间隔" I( |; M! E( ^/ k9 V" x8 S
! c+ g; b5 t4 j+ p2 ^" K# {) MRes中的另一可便之处是间隔(或插入)符号。实际上,这一符号相当于一个OR语句并代表|符号。下面的语句返回文件sample.txt中的“nerd” 和 “merd”的句柄:; G$ m4 \9 f7 A% T. p( j
# C5 t* j: R; E/ @' f
egrep “(n|m)erd” sample.txt 1 a% [# x) D# z) z% V. E2 O$ N; T9 |+ X F
间隔功能非常强大,特别是当你寻找文件不同拼写的时候,但你可以在下面的例子得到相同的结果:. ?. D l* S* e0 M: J
/ p( I% z3 H+ o P, q
egrep “[nm]erd” sample.txt $ S0 s5 z/ l' D% W1 w" y$ Z ! ^8 _! \) \9 {' Y) ^当你使用间隔功能与Res的高级特性连接在一起时,它的真正用处更能体现出来。 % m5 h4 B; z* l3 ^9 L2 h
: s9 `1 P7 Y% w+ V3 n. i第四部分: $ K* b, x6 k) e T" u* \----------------8 g8 {9 }, a& N$ d
一些保留字符 ^# i( y' `6 P9 C" t
Res的最后一个最重要特性是保留字符(也称特定字符)。例如,如果你想要查找“ne*rd”和“ni*rd”的字符,格式匹配语句“n[ei]*rd”与“neeeeerd” 和 “nieieierd”相符合,但并不是你要查找的字符。因为‘*’(星号)是个保留字符,你必须用一个反斜线符号来替代它,即:“n[ei]\*rd”。其它的保留字符包括: ' \% t9 |9 e" b$ n2 L) \" i' r: H + W6 V' k+ Z0 z# h! b6 U7 v: J^ (carat) v `- ?+ [4 H
. (period) 9 n3 M9 t) j! e+ e% R$ K
[ (left bracket} , v, B+ ]7 S$ w' q; n6 f
$ (dollar sign) , B* b" e7 N- n6 ?- H
( (left parenthesis) + C* V" I+ Q1 z7 O
) (right parenthesis) " |0 Q+ i4 w* j
| (pipe) : v( f% j O9 U, @. ?# d
* (asterisk) 8 `* a- e* j) E# k
+ (plus symbol) 0 Q4 D4 N- Q x, L+ m? (question mark) 8 N9 U! q9 |- Y9 |6 Y, y N0 C{ (left curly bracket, or left brace) : S( W9 L9 V5 V' Q; c
\ backslash : G' a2 G) J: W1 F9 v% W# m
一旦你把以上这些字符包括在你的字符搜索中,毫无疑问Res变得非常的难读。比如说以下的PHP中的eregi搜索引擎代码就很难读了。 / W5 J3 T9 Z9 K1 C4 ^* m4 z4 Q' m8 W- n4 l) [ a; E" F
eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*$",$sendto) * {8 \) t9 V- L. P/ p + u. [- E V2 s5 Z9 c. J5 r你可以看到,程序的意图很难把握。但如果你抛开保留字符,你常常会错误地理解代码的意思。 m6 e) G( j) ~" x @8 \
4 M, t# s$ ] F' V4 x6 {
总结# w, ^& j0 t, y" u) s' T( ^5 ~
在本文中,我们揭开了正则表达式的神秘面纱,并列出了ERE标准的通用语法。如果你想阅览Open Group组织的规则的完整描述,你可以参见:Regular Expressions,欢迎你在其中的讨论区发表你的问题或观点。 & U9 D0 L. P; M: D. J" n& \