谁知道“正则表达式”是什么意思

[superlink]

我一直不明白“正则表达式”是什么意思，谁能给给我说说。

[yaly]

那是编译原理中的词语.
请看看编译原理的书.

[上将军]

正则表达式
如果原来没有使用过正则表达式，那么可能对这个术语和概念会不太熟悉。不过，它们并不是您想象的那么新奇。

请回想一下在硬盘上是如何查找文件的。您肯定会使用 ? 和 * 字符来帮助查找您正寻找的文件。? 字符匹配文件名中的单个字符，而 * 则匹配一个或多个字符。一个如 'data?.dat' 的模式可以找到下述文件：

data1.dat

data2.dat

datax.dat

dataN.dat

如果使用 * 字符代替 ? 字符，则将扩大找到的文件数量。'data*.dat' 可以匹配下述所有文件名：

data.dat

data1.dat

data2.dat

data12.dat

datax.dat

dataXYZ.dat

尽管这种搜索文件的方法肯定很有用，但也十分有限。? 和 * 通配符的有限能力可以使你对正则表达式能做什么有一个概念，不过正则表达式的功能更强大，也更灵活。

[superlink]

请给出定义和简单描述，谢谢！

[上将军]

现在才明白正则表达式是regular expression，看来英文比中文要好理解多了，就是检查表达式符
不符合规定！！正则表达式有一个功能十分强大而又十分复杂的对象RegExp，在JavaScript1.2 版本以
上提供。
下面我们看看有关正则表达式的介绍：
正则表达式对象用来规范一个规范的表达式(也就是表达式符不符合特定的要求，比如是不是Email
地址格式等)，它具有用来检查给出的字符串是否符合规则的属性和方法。
除此之外，你用RegExp构造器建立的个别正则表达式对象的属性，就已经预先定义好了正则表达式
对象的静态属性，你可以随时使用它们。

[skyyoung]

javascript例子：

Use regular expressions to validate/format a string
This is an impressive collection (that I found somehere on the Net) of various functions to validate or format string in Javascript. The code is very compact.

/*******************************************************************************
FILE: RegExpValidate.js

DESCRIPTION: This file contains a library of validation functions
using javascript regular expressions. Library also contains functions that re-
format fields for display or for storage.


VALIDATION FUNCTIONS:

validateEmail - checks format of email address
validateUSPhone - checks format of US phone number
validateNumeric - checks for valid numeric value
validateInteger - checks for valid integer value
validateNotEmpty - checks for blank form field
validateUSZip - checks for valid US zip code
validateUSDate - checks for valid date in US format
validateValue - checks a string against supplied pattern

FORMAT FUNCTIONS:

rightTrim - removes trailing spaces from a string
leftTrim - removes leading spaces from a string
trimAll - removes leading and trailing spaces from a string
removeCurrency - removes currency formatting characters (), $
addCurrency - inserts currency formatting characters
removeCommas - removes comma separators from a number
addCommas - adds comma separators to a number
removeCharacters - removes characters from a string that match passed pattern


AUTHOR: Karen Gayda

DATE: 03/24/2000
*******************************************************************************/

function validateEmail( strValue) {
/************************************************
DESCRIPTION: Validates that a string contains a
valid email pattern.

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.

REMARKS: Accounts for email with country appended
does not validate that email contains valid URL
type (.com, .gov, etc.) or valid country suffix.
*************************************************/
var objRegExp = /(^[a-z]([a-z_\.]*)@([a-z_\.]*)([.][a-z]{3})$)|(^[a-z]([a-z_\.]*)@([a-z_\.]*)(\.[a-z]{3})(\.[a-z]{2})*$)/i;

//check for valid email
return objRegExp.test(strValue);
}

function validateUSPhone( strValue ) {
/************************************************
DESCRIPTION: Validates that a string contains valid
US phone pattern.
Ex. [phone] or [phone]

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.
*************************************************/
var objRegExp = /^\([1-9]\d{2}\)\s?\d{3}\-\d{4}$/;

//check for valid us phone with or without space between
//area code
return objRegExp.test(strValue);
}

function validateNumeric( strValue ) {
/******************************************************************************
DESCRIPTION: Validates that a string contains only valid numbers.

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.
******************************************************************************/
var objRegExp = /(^-?\d\d*\.\d*$)|(^-?\d\d*$)|(^-?\.\d\d*$)/;

//check for numeric characters
return objRegExp.test(strValue);
}

function validateInteger( strValue ) {
/************************************************
DESCRIPTION: Validates that a string contains only
valid integer number.

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.
******************************************************************************/
var objRegExp = /(^-?\d\d*$)/;

//check for integer characters
return objRegExp.test(strValue);
}

function validateNotEmpty( strValue ) {
/************************************************
DESCRIPTION: Validates that a string is not all
blank (whitespace) characters.

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.
*************************************************/
var strTemp = strValue;
strTemp = trimAll(strTemp);
if(strTemp.length > 0){
return true;
}
return false;
}

function validateUSZip( strValue ) {
/************************************************
DESCRIPTION: Validates that a string a United
States zip code in 5 digit format or zip+4
format. 99999 or 99999-9999

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.

*************************************************/
var objRegExp = /(^\d{5}$)|(^\d{5}-\d{4}$)/;

//check for valid US Zipcode
return objRegExp.test(strValue);
}

function validateUSDate( strValue ) {
/************************************************
DESCRIPTION: Validates that a string contains only
valid dates with 2 digit month, 2 digit day,
4 digit year. Date separator can be ., -, or /.
Uses combination of regular expressions and
string parsing to validate date.
Ex. mm/dd/yyyy or mm-dd-yyyy or mm.dd.yyyy

PARAMETERS:
strValue - String to be tested for validity

RETURNS:
True if valid, otherwise false.

REMARKS:
Avoids some of the limitations of the Date.parse()
method such as the date separator character.
*************************************************/
var objRegExp = /^\d{1,2}(\-|\/|\.)\d{1,2}\1\d{4}$/

//check to see if in correct format
if(!objRegExp.test(strValue))
return false; //doesn't match pattern, bad date
else{
var strSeparator = strValue.substring(2,3) //find date separator
var arrayDate = strValue.split(strSeparator); //split date into month, day, year
//create a lookup for months not equal to Feb.
var arrayLookup = { '01' : 31,'03' : 31, '04' : 30,'05' : 31,'06' : 30,'07' : 31,
'08' : 31,'09' : 30,'10' : 31,'11' : 30,'12' : 31}
var intDay = parseInt(arrayDate[1]);

//check if month value and day value agree
if(arrayLookup[arrayDate[0]] != null) {
if(intDay <= arrayLookup[arrayDate[0]] && intDay != 0)
return true; //found in lookup table, good date
}

//check for February
var intYear = parseInt(arrayDate[2]);
var intMonth = parseInt(arrayDate[0]);
if( ((intYear % 4 == 0 && intDay <= 29) || (intYear % 4 != 0 && intDay <=28)) && intDay !=0)
return true; //Feb. had valid number of days
}
return false; //any other values, bad date
}

function validateValue( strValue, strMatchPattern ) {
/************************************************
DESCRIPTION: Validates that a string a matches
a valid regular expression value.

PARAMETERS:
strValue - String to be tested for validity
strMatchPattern - String containing a valid
regular expression match pattern.

RETURNS:
True if valid, otherwise false.
*************************************************/
var objRegExp = new RegExp( strMatchPattern);

//check if string matches pattern
return objRegExp.test(strValue);
}


function rightTrim( strValue ) {
/************************************************
DESCRIPTION: Trims trailing whitespace chars.

PARAMETERS:
strValue - String to be trimmed.

RETURNS:
Source string with right whitespaces removed.
*************************************************/
var objRegExp = /^([\w\W]*)(\b\s*)$/;

if(objRegExp.test(strValue)) {
//remove trailing a whitespace characters
strValue = strValue.replace(objRegExp, '$1');
}
return strValue;
}

function leftTrim( strValue ) {
/************************************************
DESCRIPTION: Trims leading whitespace chars.

PARAMETERS:
strValue - String to be trimmed

RETURNS:
Source string with left whitespaces removed.
*************************************************/
var objRegExp = /^(\s*)(\b[\w\W]*)$/;

if(objRegExp.test(strValue)) {
//remove leading a whitespace characters
strValue = strValue.replace(objRegExp, '$2');
}
return strValue;
}

function trimAll( strValue ) {
/************************************************
DESCRIPTION: Removes leading and trailing spaces.

PARAMETERS: Source string from which spaces will
be removed;

RETURNS: Source string with whitespaces removed.
*************************************************/
var objRegExp = /^(\s*)$/;

//check for all spaces
if(objRegExp.test(strValue)) {
strValue = strValue.replace(objRegExp, '');
if( strValue.length == 0)
return strValue;
}

//check for leading & trailing spaces
objRegExp = /^(\s*)([\W\w]*)(\b\s*$)/;
if(objRegExp.test(strValue)) {
//remove leading and trailing whitespace characters
strValue = strValue.replace(objRegExp, '$2');
}
return strValue;
}

function removeCurrency( strValue ) {
/************************************************
DESCRIPTION: Removes currency formatting from
source string.

PARAMETERS:
strValue - Source string from which currency formatting
will be removed;

RETURNS: Source string with commas removed.
*************************************************/
var objRegExp = /\(/;
var strMinus = '';

//check if negative
if(objRegExp.test(strValue)){
strMinus = '-';
}

objRegExp = /\)|\(|[,]/g;
strValue = strValue.replace(objRegExp,'');
if(strValue.indexOf('$') >= 0){
strValue = strValue.substring(1, strValue.length);
}
return strMinus + strValue;
}

function addCurrency( strValue ) {
/************************************************
DESCRIPTION: Formats a number as currency.

PARAMETERS:
strValue - Source string to be formatted

REMARKS: Assumes number passed is a valid
numeric value in the rounded to 2 decimal
places. If not, returns original value.
*************************************************/
var objRegExp = /-?[0-9]+\.[0-9]{2}$/;

if( objRegExp.test(strValue)) {
objRegExp.compile('^-');
strValue = addCommas(strValue);
if (objRegExp.test(strValue)){
strValue = '(' + strValue.replace(objRegExp,'') + ')';
}
return '$' + strValue;
}
else
return strValue;
}

function removeCommas( strValue ) {
/************************************************
DESCRIPTION: Removes commas from source string.

PARAMETERS:
strValue - Source string from which commas will
be removed;

RETURNS: Source string with commas removed.
*************************************************/
var objRegExp = /,/g; //search for commas globally

//replace all matches with empty strings
return strValue.replace(objRegExp,'');
}

function addCommas( strValue ) {
/************************************************
DESCRIPTION: Inserts commas into numeric string.

PARAMETERS:
strValue - source string containing commas.

RETURNS: String modified with comma grouping if
source was all numeric, otherwise source is
returned.

REMARKS: Used with integers or numbers with
2 or less decimal places.
*************************************************/
var objRegExp = new RegExp('(-?[0-9]+)([0-9]{3})');

//check for match to search criteria
while(objRegExp.test(strValue)) {
//replace original string with first group match,
//a comma, then second group match
strValue = strValue.replace(objRegExp, '$1,$2');
}
return strValue;
}

function removeCharacters( strValue, strMatchPattern ) {
/************************************************
DESCRIPTION: Removes characters from a source string
based upon matches of the supplied pattern.

PARAMETERS:
strValue - source string containing number.

RETURNS: String modified with characters
matching search pattern removed

USAGE: strNoSpaces = removeCharacters( ' sfdf dfd',
'\s*')
*************************************************/
var objRegExp = new RegExp( strMatchPattern, 'gi' );

//replace passed pattern matches with blanks
return strValue.replace(objRegExp,'');
}