search
HomeBackend DevelopmentPHP TutorialRegular expressions in PHP (2)_PHP tutorial
Regular expressions in PHP (2)_PHP tutorialJul 20, 2016 am 10:59 AM
phptwoAppearmatchletternumberregularKnowSureexpressionrepeat

​ Determined to reoccur
By now, you already know how to match a letter or number, but more often than not, you may want to match a word or a group of numbers. A word consists of several letters, and a group of numbers consists of several singular numbers. The curly braces ({}) following a character or character cluster are used to determine the number of times the preceding content is repeated.
Character cluster meaning
^[a-zA-Z_]$ All letters and underscores
^[[:alpha:]]{3}$ All 3-letter words
^a$ letter a
^a{4}$ aaaa
^a{2,4}$ aa,aaa or aaaa
^a{1,3}$ a,aa or aaa
^a{2,}$ A string containing more than two a's
^a{2,} such as: aardvark and aaab, but not apple
a{2,} such as: baad and aaa, but not Nantucket
t{2} two tab characters
.{2} All two characters
These examples describe three different uses of curly braces. A number, {x} means "the preceding character or character cluster appears only x times"; a number plus a comma, {x,} means "the preceding content appears x or more times"; two Comma-separated numbers, {x,y} means "the previous content appears at least x times, but not more than y times". We can extend the pattern to more words or numbers:
^[a-zA-Z0-9_]{1,}$ //All strings containing more than one letter, number or underscore
^[0-9]{1,}$ //All positive numbers
^-{0,1}[0-9]{1,}$ //All integers
^-{0,1}[0-9]{0,}.{0,1}[0-9]{0,}$ //All decimals
The last example is not easy to understand, is it? Look at it this way: with everything starting with an optional negative sign (-{0,1}) (^), followed by 0 or more digits ([0-9]{0,}), and an optional A decimal point (.{0,1}) followed by 0 or more digits ([0-9]{0,}) and nothing else ($). Below you will learn about the simpler methods you can use.
The special character "?" is equivalent to {0,1}, they both represent: "0 or 1 previous content" or "the previous content is optional". So the example just now can be simplified to:
^-?[0-9]{0,}.?[0-9]{0,}$
The special character "*" is equivalent to {0,}, and they both represent "0 or more previous contents". Finally, the character "+" is equal to {1,}, which means "1 or more previous contents", so the above 4 examples can be written as:
^[a-zA-Z0-9_]+$ //All strings containing more than one letter, number or underscore
^[0-9]+$ //All positive numbers
^-?[0-9]+$ //All integers
^-?[0-9]*.?[0-9]*$ //All decimals
Of course this doesn't technically reduce the complexity of regular expressions, but it makes them easier to read.

www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/445602.htmlTechArticle Identifying Recurrences By now you already know how to match a letter or number, but there are more cases , possibly matching a word or a set of numbers. A word has several...
Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
php怎么把负数转为正整数php怎么把负数转为正整数Apr 19, 2022 pm 08:59 PM

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

php怎么实现几秒后执行一个函数php怎么实现几秒后执行一个函数Apr 24, 2022 pm 01:12 PM

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php怎么除以100保留两位小数php怎么除以100保留两位小数Apr 22, 2022 pm 06:23 PM

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

php怎么根据年月日判断是一年的第几天php怎么根据年月日判断是一年的第几天Apr 22, 2022 pm 05:02 PM

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php字符串有没有下标php字符串有没有下标Apr 24, 2022 am 11:49 AM

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

php怎么替换nbsp空格符php怎么替换nbsp空格符Apr 24, 2022 pm 02:55 PM

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\&nbsp\;||\xc2\xa0)/","其他字符",$str)”语句。

php怎么判断有没有小数点php怎么判断有没有小数点Apr 20, 2022 pm 08:12 PM

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php怎么读取字符串后几个字符php怎么读取字符串后几个字符Apr 22, 2022 pm 08:31 PM

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

Atom editor mac version download

Atom editor mac version download

The most popular open source editor

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),