Home > Articles > Operating Systems, Server > Linux/UNIX/Open Source

This chapter is from the book

Filename Generation/Pathname Expansion


Wildcards, globbing

When you specify an abbreviated filename that contains special characters, also called metacharacters, the shell can generate filenames that match the names of existing files. These special characters are also referred to as wildcards because they act much as the jokers do in a deck of cards. When one of these characters appears in an argument on the command line, the shell expands that argument in sorted order into a list of filenames and passes the list to the program called by the command line. Filenames that contain these special characters are called ambiguous file references because they do not refer to one specific file. The process the shell performs on these filenames is called pathname expansion or globbing.

Ambiguous file references can quickly refer to a group of files with similar names, saving the effort of typing the names individually. They can also help find a file whose name you do not remember in its entirety. If no filename matches the ambiguous file reference, the shell generally passes the unexpanded reference—special characters and all—to the command. See “Brace Expansion” on page 411 for a technique that generates strings that do not necessarily match filenames.

The ? Special Character

The question mark (?) is a special character that causes the shell to generate filenames. It matches any single character in the name of an existing file. The following command uses this special character in an argument to the lpr utility:

$ lpr memo?

The shell expands the memo? argument and generates a list of files in the working directory that have names composed of memo followed by any single character. The shell then passes this list to lpr. The lpr utility never “knows” the shell generated the filenames it was called with. If no filename matches the ambiguous file reference, the shell passes the string itself (memo?) to lpr or, if it is set up to do so, passes a null string (see nullglob on page 408).

The following example uses ls first to display the names of all files in the working directory and then to display the filenames that memo? matches:

$ ls
mem   memo12  memo9  memomax   newmemo5
memo  memo5   memoa  memos

$ ls memo?
memo5  memo9  memoa  memos

The memo? ambiguous file reference does not match mem, memo, memo12, memomax, or newmemo5. You can also use a question mark in the middle of an ambiguous file reference:

$ ls
7may4report  may4report      mayqreport  may_report
may14report  may4report.79   mayreport   may.report

$ ls may?report
may4report  mayqreport  may_report  may.report


You can use echo and ls to practice generating filenames. The echo builtin displays the arguments the shell passes to it:

$ echo may?report
may4report mayqreport may_report may.report

The shell first expands the ambiguous file reference into a list of files in the working directory that match the string may?report. It then passes this list to echo, as though you had entered the list of filenames as arguments to echo. The echo utility displays the list of filenames.

A question mark does not match a leading period (one that indicates a hidden filename; page 188). When you want to match filenames that begin with a period, you must explicitly include the period in the ambiguous file reference.

The * Special Character

The asterisk (*) performs a function similar to that of the question mark but matches any number of characters, including zero characters, in a filename. The following example first shows all files in the working directory and then shows commands that display all the filenames that begin with the string memo, end with the string mo, and contain the string alx:

$ ls
amemo  memalx  memo.0612  memoalx.0620  memorandum  sallymemo
mem    memo    memoa      memoalx.keep  memosally   user.memo

$ echo memo*
memo memo.0612 memoa memoalx.0620 memoalx.keep memorandum memosally

$ echo *mo
amemo memo sallymemo user.memo

$ echo *alx*
memalx memoalx.0620 memoalx.keep

The ambiguous file reference memo* does not match amemo, mem, sallymemo, or user.memo. Like the question mark, an asterisk does not match a leading period in a filename.

The –a option causes ls to display hidden filenames (page 188). The command echo * does not display . (the working directory), .. (the parent of the working directory), .aaa, or .profile. In contrast, the command echo .* displays only those four names:

$ ls
aaa  memo.0612  memo.sally  report  sally.0612  saturday  thurs

$ ls -a
.   aaa   memo.0612   .profile  sally.0612  thurs
..  .aaa  memo.sally  report    saturday

$ echo *
aaa memo.0612 memo.sally report sally.0612 saturday thurs

$ echo .*
. .. .aaa .profile

In the following example, .p* does not match memo.0612, private, reminder, or report. The ls .* command causes ls to list .private and .profile in addition to the contents of the . directory (the working directory) and the .. directory (the parent of the working directory). When called with the same argument, echo displays the names of files (including directories) in the working directory that begin with a dot (.) but not the contents of directories.

$  ls -a
.  ..  memo.0612  private  .private  .profile  reminder  report

$ echo .p*
.private .profile

$ ls . *
.private .profile
memo.0612  private    reminder   report

$ echo .*
. .. .private .profile

You can plan to take advantage of ambiguous file references when you establish conventions for naming files. For example, when you end the names of all text files with .txt, you can reference that group of files with *.txt. The next command uses this convention to send all text files in the working directory to the printer. The ampersand causes lpr to run in the background.

$ lpr *.txt &

The [ ] Special Characters

A pair of brackets surrounding one or more characters causes the shell to match filenames containing the individual characters within the brackets. Whereas memo? matches memo followed by any character, memo[17a] is more restrictive: It matches only memo1, memo7, and memoa. The brackets define a character class that includes all the characters within the brackets. (GNU calls this a character list; a GNU character class is something different.) The shell expands an argument that includes a character-class definition by substituting each member of the character class, one at a time, in place of the brackets and their contents. The shell then passes the list of matching filenames to the program it is calling.

Each character-class definition can replace only a single character within a filename. The brackets and their contents are like a question mark that substitutes only the members of the character class.

The first of the following commands lists the names of all files in the working directory that begin with a, e, i, o, or u. The second command displays the contents of the files named page2.txt, page4.txt, page6.txt, and page8.txt.

$ echo [aeiou]*

$ less page[2468].txt

A hyphen within brackets defines a range of characters within a character-class definition. For example, [6–9] represents [6789], [a–z] represents all lowercase letters in English, and [a–zA–Z] represents all letters, both uppercase and lowercase, in English.

The following command lines show three ways to print the files named part0, part1, part2, part3, and part5. Each of these command lines causes the shell to call lpr with five filenames:

$ lpr part0 part1 part2 part3 part5

$ lpr part[01235]

$ lpr part[0-35]

The first command line explicitly specifies the five filenames. The second and third command lines use ambiguous file references, incorporating character-class definitions. The shell expands the argument on the second command line to include all files that have names beginning with part and ending with any of the characters in the character class. The character class is explicitly defined as 0, 1, 2, 3, and 5. The third command line also uses a character-class definition but defines the character class to be all characters in the range 0–3 plus 5.

The following command line prints 39 files, part0 through part38:

$ lpr part[0-9] part[12][0-9] part3[0-8]

The first of the following commands lists the files in the working directory whose names start with a through m. The second lists files whose names end with x, y, or z.

$ echo [a-m] *

$ echo * [x-z]

The next example demonstrates that the ls utility cannot interpret ambiguous file references. First ls is called with an argument of ?old. The shell expands ?old into a matching filename, hold, and passes that name to ls. The second command is the same as the first, except the ? is quoted (by preceding it with a backslash [\]; refer to “Special Characters” on page 150). Because the ? is quoted, the shell does not recognize it as a special character and passes it to ls. The ls utility generates an error message saying that it cannot find a file named ?old (because there is no file named ?old).

$ ls ?old

$ ls \?old
ls: ?old: No such file or directory

Like most utilities and programs, ls cannot interpret ambiguous file references; that work is left to the shell.

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