正则入门连载！（献给不及格的程序员们）第3/4页

发布：dxy 发布日期：2007-2-5 字体：[增加减小] 类型：转载

优先级顺序
说明如何计算正则表达式以及正则表达式的序列和语法对结果有何影响。

点击运行可以看到效果:

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<HTML xmlns:MSHelp="http://msdn.microsoft.com/mshelp" DIR="LTR"> 
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div#scrtext /* Creates the text area in a full-scroll topic */ 
    {   /* Allows topic to scroll. */ 
/*    width: 100%; /* Forces tables to have correct right margin */*/ 
    padding: 0px 10px 0px 22px;  
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div#bannerrow1 /* provides full-width color to top row in running head (requires script) */ 
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    background-color: #99ccff; 
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div#titlerow /* provides non-scroll topic title area (requires script) */ 
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    width: 100%; /* Forces tables to have correct right margin */ 
    padding: 0px 10px 0px 22px;  
    background-color: #99ccff;         
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/* -------------------------------------------------- 
                    HEADING STYLES 
-------------------------------------------------- */

h1, h2, h3, h4 
    { 
    font-family: 瀹嬩綋, Verdana, Arial, Helvetica, sans-serif; 
    margin-bottom: .4em;  
    margin-top: 1em; 
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h1 
    { 
    font-size: 120%; 
    margin-top: 0em; 
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div#scrollyes h1 /* Changes font size for full-scrolling topic */ 
    { 
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h2 
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h3 
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h4 
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.dtH1, .dtH2, .dtH3, .dtH4 
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div#titlerow h1 
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p 
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blockquote.dtBlock 
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div#dtHoverText 
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    color: #000066; 
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.normal 
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    margin: .5em 0em .5em 0em; 
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.fineprint 
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    font-size: 110%; /* 90% of 70% */ 
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.indent 
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    margin: .5em 1.5em .5em 1.5em; 
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.topicstatus /* Topic Status Boilerplate class */ 
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    color: red; 
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/* -------------------------------------------------- 
                     LABEL STYLES 
-------------------------------------------------- */

p.label 
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    margin-top: 1em; 
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p.labelproc 
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    margin-top: 1em; 
    color: #000066; 
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/* -------------------------------------------------- 
                    GRAPHIC STYLES 
-------------------------------------------------- */

img 
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    border: none;  
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/* -------------------------------------------------- 
                     LIST STYLES 
-------------------------------------------------- */

ol, ul 
    { 
    margin: .5em 0em 0em 2em;  
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li 
    { 
    margin-bottom: .5em; 
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ul p, ol p, dl p 
    { 
    margin-left: 0em; 
    } 
ul p.label, ol p.label 
    { 
    margin-top: .5em; 
    }

/* -------------------------------------------------- 
               DEFINITION LIST STYLES 
-------------------------------------------------- */

dl 
    { 
    margin-top: 0em;  
    padding-left: 1px; /* Prevents italic-letter descenders from being cut off */ 
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dd 
    { 
    margin-bottom: 0em;   
    margin-left: 1.5em;  
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dt 
    { 
    margin-top: .5em;  
    }

/* -------------------------------------------------- 
           CODE, SYNTAX, and REFTIP STYLES 
-------------------------------------------------- */

pre 
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    margin-top: .5em; 
    margin-bottom: .5em;  
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pre, code, .code 
    { 
    font: 100% 瀹嬩綋, Courier New, Monospace, Courier;/* This is 100% of 70% */ 
    color: #000066; 
    } 
pre b, code b 
    { 
    letter-spacing: .1em; /* opens kerning on bold in Syntax/Code */ 
    } 
pre.syntax 
    { 
    font: 100% Courier New, 瀹嬩綋, Monospace, Courier;/* This is 100% of 70% */ 
    background: #cccccc; 
    padding: 4px 8px; 
    cursor: text; 
    margin-top: 1em; 
    margin-bottom: 1em;  
    color: #000000; 
    border-width: 1px; 
    border-style: solid; 
    border-color: #999999; 
    }

/* -------------------------------------------------- 
                      LINK STYLES 
-------------------------------------------------- */

a:link 
    { 
    color: #0000ff; 
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a:visited 
    { 
    color: #0000ff; 
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a:hover 
    { 
    color: #3366ff; 
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/* --------------------------- 
MSHelp\:link - Help HxLinks 
--------------------------- */ 
MSHelp\:link 
    { 
    text-decoration: underline;  
    color: #0000ff;  
    hoverColor: #3366ff; 
    filterString: ; 
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A.HxLinkTable /* MSHelp\:link - Table disambiguation elements */ 
    { 
    } 
/* --------------------------- 
MSHelp\:ktable - Help links 
--------------------------- */ 
MSHelp\:ktable 
    { 
    disambiguator: span; 
    separator:  |  
    prefix: |  
    postfix:   
    filterString: ; 
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div.HxLinkTable 
    { 
    width: auto; /* Forces tables to have correct right margins and top spacing */ 
    margin-top: -.4em; 
    visibility: visible; 
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ol div.HxLinkTable, ul div.HxLinkTable 
    { 
    margin-top: 0em; /* Forces tables to have correct right margins and top spacing */ 
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table.HxLinkTable /* Keep in sync with general table settings below */ 
    { 
    width: auto; 
    margin-top: 1.5em; 
    margin-bottom: .3em; 
    margin-left: -1em; 
    border-width: 1px 1px 0px 0px; 
    border-style: solid; 
    border-color: #999999; 
    background-color: #999999;  
    font-size: 100%; /* Text in Table is same size as text outside table */ 
    behavior:url(hxlinktable.htc); /* Attach the behavior to link elements. */ 
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table.HxLinkTable th, table.HxLinkTable td /* Keep in sync with general table settings below */ 
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    border-style: solid; /* Creates the cell border and color */ 
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table.HxLinkTable th /* Keep in sync with general table settings below */ 
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    vertical-align: bottom; 
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table.HxLinkTable td /* Keep in sync with general table settings below */ 
    { 
    background: #ffffff; 
    vertical-align: top; 
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/* -------------------------------------------------- 
                    TABLE STYLES 
-------------------------------------------------- */

div.tablediv 
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    width: 100%; /* Forces tables to have correct right margins and top spacing */ 
    margin-top: -.4em; 
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ol div.tablediv, ul div.tablediv, ol div.HxLinkTable, ul div.HxLinkTable 
    { 
    margin-top: 0em; /* Forces tables to have correct right margins and top spacing */ 
    } 
table.dtTABLE 
    { 
    width: 100%; /* Forces tables to have correct right margin */ 
    margin-top: .6em; 
    margin-bottom: .3em; 
    border-width: 1px 1px 0px 0px; 
    border-style: solid; 
    border-color: #999999; 
    background-color: #999999;  
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table.dtTABLE th, table.dtTABLE td 
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    border-style: solid; /* Creates the cell border and color */ 
    border-width: 0px 0px 1px 1px; 
    border-style: solid; 
    border-color: #999999; 
    padding: 4px 6px; 
    text-align: left; 
    } 
table.dtTABLE th     
    {  
    background: #cccccc; /* Creates the shaded table header row */ 
    vertical-align: bottom; 
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table.dtTABLE td     
    { 
    background: #ffffff; 
    vertical-align: top; 
    }

/* -------------------------------------------------- 
ISSUE REPORTING AND MISC LINKS TOPIC FOOTER 
-------------------------------------------------- */

div.footer 
    { 
     
    } 
div.footer hr 
    { 
    color: #999999; 
    height: 1px; 
    }

/* -------------------------------------------------- 
             STYLES FOR RUNNING HEADS 
-------------------------------------------------- */

table.bannerparthead, table.bannertitle /* General values for the Running Head tables */ 
    { 
    position: relative; 
    left: 0px; 
    top: 0px; 
    padding: 0px 0px 0px 0px; 
    margin: 0px 0px 0px 0px; 
    width: 100%; 
    height: 21px;  
    border-collapse: collapse; 
    border-style: solid; 
    border-width: 0px; 
    background-color: #99ccff;  
    font-size: 100%; 
    } 
table.bannerparthead td /* General Values for cells in the top row of running head */ 
    { 
    margin: 0px 0px 0px 0px; 
    padding: 2px 0px 0px 4px; 
    vertical-align: middle; 
    /*border-width: 0px 0px 1px 0px; */ 
    border-width: 0px 
    border-style: solid; 
    border-color: #999999; 
    background: transparent;  
    /* font-style: normal; */ 
    font-weight: normal; 
    } 
table.bannerparthead td.product /* Values for top right cell in running head */ 
    {                       /* Allows for a second text block in the running head */ 
    text-align: right; 
    padding: 2px 5px 0px 5px; 
    } 
table.bannertitle td /* General Values for cells in the bottom row of running head */ 
    { 
    margin: 0px 0px 0px 0px; 
    padding: 0px 0px 0px 3px; 
    vertical-align: middle; 
    border-width: 0px 0px 1px 0px; 
    border-style: solid; 
    border-color: #999999; 
    background: transparent; 
    font-weight: bold; 
    } 
td.button1 /* Values for button cells */ 
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    width: 14px; 
    cursor: hand; 
    }

/* ================================================= 
            STYLES REQUIRED BY THE SCRIPT */

/* -------------------------------------------------- 
                  SAMPLE VIEWER 
-------------------------------------------------- */

div#smpMgrCell 
    { 
    display:none; 
    } 
table.SampMgr 
    { 
    margin: 0px 0px 0px -22px; 
    } 
table.SampMgr td 
    { 
    padding-left: 22px; 
    }

/* -------------------------------------------------- 
RUNNING HEAD BAR POPUP STYLES: See Also, Requirements, MultiLang Filtering 
-------------------------------------------------- */

div.sapop, div.langMenu /* See Also & Requirements popups */ 
    { 
    position: absolute; 
    left: 0px; 
    z-index: 1; 
    width: 50%; 
    padding: 0px 8px 5px 26px; 
    visibility: hidden; 
    border: 1px solid #999999; /* Same as all other border colors */ 
    background: #ffffcc; 
    } 
div.langMenu /* MultiLang Filter popup */ 
    { 
    padding: 10px 10px 10px 10px; 
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div.langMenu ul 
    { 
    list-style-type: none; 
    padding-left: 5px; 
    margin-left: 0px; 
    } 
.lang, .ilang /* controls the multilang tag styles */ 
    { 
    color: #333333; 
    font-family: Verdana, Arial, 瀹嬩綋, Helvetica, sans-serif; 
    font-size: 80%; 
    font-weight: normal; 
    font-style: normal; 
    } 
h1 .lang, h1 .ilang  
    { 
    font-size: 80%; 
    } 
div.filtered 
    { 
    margin-top: .6em; 
    margin-bottom: .6em; 
    margin-left: -7px; 
    padding: 0px 0px 0px 6px; 
    border-left: 1px solid #999999; 
    background: #ffffff; 
    } 
div.filtered h1, div.filtered h2, div.filtered h3, div.filtered h4 
    { 
    margin-left: -22px; 
    } 
div.filtered span.lang 
    { 
    position: relative; 
    left: 0px; 
    }

/* -------------------------------------------------- 
              PARAMETER POPUP STYLES 
-------------------------------------------------- */

div.reftip /* Defines the RefTip popup in Syntax */ 
    { 
    position: absolute; 
    z-index: 1; 
    visibility: hidden; 
    border: 1px solid #999999; 
    background: #ffffcc; 
/*    padding: 0px 0px 0px 0px; */     
    } 
div.reftip dl /* Sets margin around the text within the popup */ 
    { 
    margin: 3px 8px 8px 8px; 
    } 
a.synParam /* parameter popup links */ 
    { 
    color: #0000ff; /* Must match the a:link style color */ 
    text-decoration: underline; 
    } 
a.synParam:visited /* ensures parameter popup links are always the unvisited color */ 
    { 
    color: #0000ff; /* Must match the a:link style color */ 
    text-decoration: underline; 
    } 
a.synParam:hover /* parameter popup links */ 
    { 
    color: #3366ff; /* Must match the a:hover style color */ 
    text-decoration: underline; 
    font-style: italic; 
    }

/* -------------------------------------------------- 
              EXPAND-COLLAPSE STYLES 
-------------------------------------------------- */

div.expandBody 
    { 
    margin: .5em 0em 0em 1.4em; 
    display:none; 
    } 
a.expandLink1 
    { 
    font-size: 115%;  
    } 
a#ExPand 
    { 
    color: #3366ff;  
    font-weight: bold;  
    text-decoration: none;  
    } 
a#ExPandAll 
    { 
    color: #3366ff;  
    font-weight: bold;  
    text-decoration: none;  
    }

/* -------------------------------------------------- 
              GLOSSARY POPUP STYLES  
          Not used by Visual Studio .NET  
-------------------------------------------------- */

/* COMMENT OUT GLOSSARY SECTION 
/*div#popUpWindow 
    { Controlled by the script in the variable L_PopUpBoxStyle_Style 
    }*/ 
a.glosslink:link 
    { 
    color: #000000; 
    } 
a.glosslink:visited 
    { 
    color: #000000;  
    } 
a.glosslink:hover 
    { 
    color: #000000; 
    font-style: italic; 
    } 
div#popUpWindow h5 /* Controls the style of the Term in Glossary Popups */ 
    { 
    margin: 5px 5px 5px 5px; 
    color: #000000; 
    } 
div#popUpWindow p /* Controls the style of the Text in Glossary Popups */ 
    { 
    margin: 5px 5px 5px 5px; 
    color: #000000; 
    } 
p.GLOSSARY_TEXT 
    { 
    } 
div#popUpWindow a /* Controls the style of the Links in Glossary Popups */ 
    { 
    }

*/ /* END COMMENT OUT OF GLOSSARY SECTION */

/* END STYLES REQUIRED BY THE SCRIPT  
================================================== */ 
</style> 
<HEAD> 
<META HTTP-EQUIV="Content-Type" Content="text/html; charset=gb2312"> 
<TITLE>优先级顺序</TITLE> 
<xml> 
<MSHelp:TOCTitle Title="优先级顺序"/> 
<MSHelp:RLTitle Title="优先级顺序 (JScript .NET)"/> 
<MSHelp:Keyword Index="A" Term="jsreconOrderOfPrecedence"/> 
<MSHelp:Keyword Index="A" Term="jsreconOrderOfPrecedence"/> 
<MSHelp:Keyword Index="K" Term="<a href="http://www.jb51.net/list/list_6_1.htm" target="_blank"><font color=red>正则</font></a>表达式, 优先级顺序"/> 
<MSHelp:Keyword Index="K" Term="优先级, <a href="http://www.jb51.net/list/list_6_1.htm" target="_blank"><font color=red>正则</font></a>表达式"/> 
<MSHelp:Keyword Index="K" Term="<a href="http://www.jb51.net/list/list_6_1.htm" target="_blank"><font color=red>正则</font></a>表达式的优先级顺序"/> 
<MSHelp:Attr Name="DevLang" Value="JScript"/> 
<MSHelp:Attr Name="DevLangVers" Value="kbJScript"/> 
<MSHelp:Attr Name="DocSet" Value="JScript"/> 
<MSHelp:Attr Name="DocSet" Value="Visual Studio"/> 
<MSHelp:Attr Name="Product" Value="VS"/> 
<MSHelp:Attr Name="ProductVers" Value="kbVS700"/> 
<MSHelp:Attr Name="Technology" Value="ManagedCode"/> 
<MSHelp:Attr Name="TechnologyVers" Value="kbManagedCode"/> 
<MSHelp:Attr Name="TopicType" Value="kbArticle"/> 
<MSHelp:Attr Name="TargetOS" Value="Windows"/> 
<MSHelp:Attr Name="Locale" Value="kbChineseSimp"/> 
</xml> 
<META name="rtfFileName" content="js7reregexp.rtf"> 
<META NAME="save" CONTENT="history"> 
 
<SCRIPT SRC="ms-help:/../commoner/scripts/dtuelink.js"></SCRIPT> 
<META NAME="msdnID" CONTENT="_731803"> 
</HEAD> 
<body topmargin=0 id="bodyID" class = "dtBODY"> 
<div id="nsbanner"> 
<div id="bannerrow1"> 
<TABLE CLASS="bannerparthead" CELLSPACING=0> 
<TR ID="hdr"> 
<TD CLASS="runninghead" nowrap>JScript .NET</TD> 
<TD CLASS="product" nowrap> </TD> 
</TR> 
</TABLE> 
</div> 
<div id="TitleRow"> 
<H1 class="dtH1"><A NAME="jsreconorderofprecedence"></A>优先级顺序</H1> 
</div></div> 
 
<DIV id="nstext" valign="bottom"> 
<a href="http://www.jb51.net/list/list_6_1.htm" target="_blank"><font color=red>正则</font></a>表达式从左到右进行计算，并遵循优先级顺序，这与算术表达式非常类似。

下表从最高到最低说明了各种<a href="http://www.jb51.net/list/list_6_1.htm" target="_blank"><font color=red>正则</font></a>表达式运算符的优先级顺序： 
<div class="tablediv"><table cellspacing="0" class="dtTABLE">

<TR VALIGN="top"> 
<TD width=40%>(), (?:), (?=), []</TD> 
<TD width=60%>括号和中括号</TD> 
</TR>

<TR VALIGN="top"> 
<TD width=40%>^, $, \<I>anymetacharacter, anycharacter</I></TD> 
<TD width=60%>定位点和序列</TD> 
</TR>

字符比替换运算符具有更高的优先级，这样使得“m|food”匹配“m”或者“food”。若要匹配“mood”或“food”，请使用括号创建子表达式，从而产生“(m|f)ood”。

<A HREF="jsreconintroductiontoregularexpressions.htm"><a href="http://www.jb51.net/list/list_6_1.htm" target="_blank"><font color=red>正则</font></a>表达式介绍</A> 
 
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<A HREF="JavaScript:sendfeedback('CHS _731803', 'VSDOCS@MICROSOFT.COM')">将文档反馈发送给 Microsoft</A> 
<MSHelp:link keywords="vxmscCopyright" TABINDEX="0">© 2002 Microsoft Corporation。保留所有权利。</MSHelp:link></div>  
</div>  
 
</BODY> 
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[Ctrl+A 全选提示:你可先修改部分代码,再按运行]

普通字符
区分普通字符与元字符，并说明如何将多个单字符正则表达式组合在一起，以创建更大的表达式。
普通字符包括没有显式指定为元字符的所有可打印和不可打印字符。这包括所有大写和小写字母、所有数字、所有标点符号和一些其他符号。
正则表达式的最简单形式是在搜索字符串中匹配其本身的单个普通字符。例如，单字符模式，如 A，不论出现在搜索字符串中的何处，它总是匹配字母 A。下面是一些单字符正则表达式模式的示例：
/a/
/7/
/M/
可以将许多单字符组合起来以形成大的表达式。例如，以下正则表达式组合了单字符表达式：a、7 和 M。
/a7M/
请注意，没有串联运算符。只须在一个字符后面键入另一个字符。
特殊字符
说明转义符的概念以及如何创建与元字符匹配的正则表达式。