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

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

Array Variables

One-dimensional arrays are supported by the Korn shell. Arrays can have a maximum of 4096 elements. Array subscripts start at 0 and go up to 4096 (or the maximum element minus one). Any variable can become a one-dimensional array by simply referring to it with a subscript. Here, variable X is set to A:

$ X=A 

By explicitly assigning X[1] a value, variable X is transformed into an array variable:

$ X[1]=B 

The original assignment to variable X is not lost. The first array element (X[0]) is still assigned A.

Table 3.6. More Variable Expansion Formats


replace all occurrences of pattern1 with pattern2 in variable


replace first occurrence of pattern1 with pattern2 in variable


replace first occurrence of pattern1 with pattern2 in variable if variable begins with pattern1


replace last occurrence of pattern1 with pattern2 in variable if variable ends with pattern1


return variable from character position start to end


return length characters from variable from character position start to end

Array Variable Assignments and Declarations

Arrays can be assigned values by using normal variable assignment statements, the set –A command, or the typeset command:

variable[0]=value variable[1]=value. . . variable[n]=value 


set –A variable value0 value1 . . . valuen 


typeset variable[0]=value variable[1]=value. . . \ 

The only difference between the formats is that with the set command format, the values are assigned to the array variable sequentially starting from element zero. In the other formats, the array elements can be assigned values in any order. This example assigns the weekday names to the array variable DAY using normal variable assignment format:

$ DAY[0]=Mon DAY[1]=Tue DAY[2]=Wed  \ 
   DAY[3]=Thu DAY[4]=Fri DAY[5]=Sat DAY[6]=Sun 

The same variable can be assigned values using the set command:

$ set —A DAY Mon Tue Wed Thu Fri Sat Sun 

or the typeset command:

$ typeset DAY[0]=Mon DAY[1]=Tue DAY[2]=Wed \ 
   DAY[3]=Thu DAY[4]=Fri DAY[5]=Sat DAY[6]=Sun 

Not all the elements of an array need to exist. You can assign values to non-successive elements of an array. Here, the first and fourth elements of the TEST array are assigned values.

$ typeset TEST[0]=a TEST[3]=b 

Table 3.7. Array Variables

${array}, $array

array element zero


array element n


array element n+2


array element $i

${array[*]}, ${array[@]}

all elements of an array

${#array[*]}, ${#array[@]}

number of array elements


length of array element n

${!array[*]}, ${!array[@]}

all initialized subscript values


x array elements starting withelement n


all array elements starting with element n

Array Variable Expansion

Array variables are expanded in the same manner as normal variables and parameters: using the $ character. Without a subscript value, an array variable refers to the first element, or element 0.

$ print $DAYS is the same as $DAY[0] 
   Mon is the same as Mon 

To access the value of a specific array variable element use a subscript. Array variable names and subscripts must be enclosed in braces for proper expansion:

$ print ${DAY[3]} ${DAY[5]} 
   Thu Sat 

If an element does not exist, nothing is substituted:

$ print ${DAY[25]} 

All the elements of an array can be accessed by using the * or @ as the subscript value. They both return the same value. These examples print the values of all the elements of the DAY array variable:

$ print ${DAY[*]} 
   Mon Tue Wed Thu Fri Sat Sun 
   $ print ${DAY[@]} 
   Mon Tue Wed Thu Fri Sat Sun 

The number of elements of an array variable is returned by using the # in front of the array variable name and using * or @ as the subscript value. Let's try it with DAY:

$ print ${#DAY[*]} 
   $ print ${#DAY[@]} 

To get values for a subset of an array, use this format:




Arithmetic expressions can be used to return a subscript value. This example prints the fifth element of the DAY array variable. Remember that array subscripts start with 0, so the third array element has a subscript of 2, and the fifth element has a subscript of 4:

$ print ${DAY[4/2]} 
   $ print ${DAY[7-6+5-4+3-2+1] 

Variable expansion can also be used to generate a subscript value.

$ X=6 
   $ print ${DAY[$X]} 

Array Variable Attributes

As with ordinary variables, attributes can be assigned to array-type variables. Arrays can also be declared, and assigned values and attributes with the typeset command:

typeset –attribute variable[0]=value variable[1]=value. . . 

Once set, attributes apply to all elements of an array. This example sets the uppercase attribute for the DAY array variable using the typeset –u command:

$ typeset —u DAY 

Now all the element values are displayed in upper case:

$ print ${DAY[*]} 

Array element attributes can be set before or after assignment. Here, XVAR is initially assigned lowercase aaa, bbb, and ccc:

$ set —A XVAR aaa bbb ccc 
   $ print ${XVAR[*]} 
   aaa bbb ccc 

Now, the uppercase, left-justify, two-character-wide attributes are set and the new element values are displayed. Notice that the third character from each element has been dropped, and the value is now in uppercase:

$ typeset —uL2 XVAR 
   $ print ${XVAR[*]} 
   AA BB CC 

Array Variable Reassignments

Besides using regular array-element[n]=value or typeset array-element[n]=value syntax to reassign values, array variables can also have their values reassigned with the set +A command:

set +A variable value0 value1 . . . 

This is helpful when you don't want to reassign values to all the elements of an array. In this example, the array variable X is assigned six values:

$ set —A X one two three d e f 
   $ print ${X[*]} 
   one two three d e f 

Using the set +A command, the first three elements are reassigned a, b, and c:

$ set +A X a b c 
   $ print ${X[*]} 
   a b c d e f 

Notice that values of the fourth, fifth, and sixth elements have not been affected.

Associative Arrays

This version of the Korn shell also supports associative arrays, that is arrays that use string subscripts rather than integer subscripts. Associative arrays are declared using this format:

typeset A variable 

where variable is the name of the associative array. Additional arguments can be given to the typeset command to specify a data type. For example, we can create an associative array to store some exchange rates:

$ typeset -AE exchange_rate 
   $  exchange_rate["DM"]=1.7 
   $  exchange_rate["FF"]=.15 
   $  exchange_rate["AS"]=.04 

To display a list of associative array subscripts:

${!variable[*]} or ${!variable[@]} 

To display the values for all or parts of an associative array:


For example, all and a specific exchange rate is displayed here:

$ print ${!exchange_rate[*]} 
   0.15 1.7 
   $ print "The DM exchange rate is:${exchange_rate[DM]}" 
  • + 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