Home > Articles

  • Print
  • + Share This
This chapter is from the book

3.10. Understanding Basic Regular Expression Syntax

You want to create a regular expression.


Regular expressions consist of a series of characters and quantifiers on those characters. The characters themselves can be literal or can be denoted by using character classes, such as \d, which denotes a digit character class, or \S, which denotes any nonwhitespace character.

Table 3.4 Regular Expression Single Character Classes




Any digit


Any nondigit


Any word character


Any nonword character


Any whitespace character


Any nonwhitespace

In addition to the single character classes, you can also specify a range or set of characters using ranged and set character classes. This ability allows you to narrow the search for a specified character by limiting characters within a specified range or within a defined set.

Table 3.5 Ranged and Set Character Classes




Any character except newline.


Any character within the Unicode character category uc.


Any literal character in the set.


Any character not within the Unicode character category uc.


Any character not in the set of literal characters.

Quantifiers work on character classes to expand the number of characters the character classes should match. You need to specify, for instance, a wildcard character on a character class, which means 0 or more characters within that class. Additionally, you can also specify a set number of matches of a class that should occur by using an integer within braces following the character class designation.

Table 3.6 Character Class Quantifiers




0 or more characters


1 or more characters


0 or 1 characters


Exactly n characters


At least n characters


At least n but no more than m characters

You can also specify where a certain regular expression should start within a string. Positional assertions allow you to, for instance, match a certain expression as long as it occurs at the beginning or ending of a string. Furthermore, you can create a regular expression that operates on a set of words within a string by using a positional assertion that continues matching on each subsequent word separated by any nonalphanumeric character.

Table 3.7 Positional (Atomic Zero-Width) Assertions




Beginning of a string or beginning of a newline


End of the string, including the newline character


End of a string before a newline character or at the end of the line


Continues where the last match left off


Beginning of a string


Between word boundaries (between alphanumeric and nonalphanumeric characters)


End of the string before the newline character


Characters not between word boundaries


Regular expressions use a variety of characters both symbolic and literal to designate how a particular string of text should be parsed. The act of parsing a string is known as matching, and when applied to a regular expression, the match will be either true or false. In other words, when you use a regular expression to match a series of characters, the match will either succeed or fail. As you can see, this process has powerful applicability in the area of input validation.

You build regular expressions using a series of character classes and quantifiers on those character classes as well as a few miscellaneous regular-expression constructs. You use character classes to match a single character based either on what type of character it is, such as a digit or letter, or whether it belongs within a specified range or set of characters (as shown in Table 3.4). Using this information, you can create a series of character classes to match a certain string of text. For instance, if you want to specify a phone number using character classes, you can use the following regular expression:


This expression begins by first escaping the left parenthesis. You must escape it because parentheses are used for grouping expressions. Next you can see three digits representing a phone number's area code followed by the closing parenthesis. You use a \s to denote a whitespace character. The remainder of the regular expression contains the remaining digits of the phone number.

In addition to the single character classes, you can also use ranged and set character classes. They give you fine-grain control on exactly the type of characters the regular expression should match. For instance, if you want to match any character as long as it is a vowel, use the following expression:


This line means that a character should match one of the literal characters within that set of characters. An even more specialized form of single character classes are Unicode character categories. Unicode categories are similar to some of the character-attribute inspection methods shown earlier in this chapter. For instance, you can use Unicode categories to match on uppercase or lowercase characters. Other categories include punctuation characters, currency symbols, and math symbols, to name a few. You can easily find the full list of Unicode categories in MSDN under the topic "Unicode Categories Enumeration."

You can optimize the phone-number expression, although it's completely valid, by using quantifiers. Quantifiers specify additional information about the character, character class, or expression to which it applies. Some quantifiers include wildcards such as *, which means 0 or more occurrences, and ?, which means only 0 or 1 occurrences of a pattern. You can also use braces containing an integer to specify how many characters within a given character class to match. Using this quantifier in the phone-number expression, you can specify that the phone number should contain three digits for the area code followed by three digits and four digits separated by a dash:


Because the regular expression itself isn't that complicated, you can still see that using quantifiers can simplify regular-expression creation. In addition to character classes and quantifiers, you can also use positional information within a regular expression. For instance, you can specify that given an input string, the regular expression should operate at the beginning of the string. You express it using the ^ character. Likewise, you can also denote the end of a string using the $ symbol. Take note that this doesn't mean start at the end of the string and attempt to make a match because that obviously seems counterintuitive; no characters exist at the end of the string. Rather, by placing the $ character following the rest of the regular expression, it means to match the string with the regular expression as long as the match occurs at the end of the string. For instance, if you want to match a sentence in which a phone number is the last portion of the sentence, you could use the following:

My phone number is (555) 555-5555 = Match
(555) 555-5555 is my phone number = Not a match
  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020