HP 3000 Manuals HP 3000 Manuals
Lesson 1 Understanding Variables Introduction Lesson 1 covers the following topics dealing with variables and how to define them: * how to create user-defined variables * how to modify user-defined and some system-defined variables * SETVAR * SHOWVAR * DELETEVAR As you become more experienced, you will probably find yourself creating more and more specialized user commands. In doing so, you will probably find the use of variables invaluable. Variables are similar to the parameters that you have already used in the past lessons. Throughout the lessons in this module, you will learn how to use both system-defined and user-defined variables in your user commands. Command files in this lesson In this lesson, you will execute command files that use variables. The tasks performed by the command files could also be performed by UDCs; however, this would involve constantly uncataloging and recataloging UDC files to add or modify UDCs. The LF and the STATS command files will be used to illustrate various aspects of variables and expressions. Also, the contents of each file serve as good review for system-defined formal files, file equations, and backreferencing.
NOTE Each of these command files could become a UDC in a UDC file if you wished.
Don't expect to understand everything about the LF and STATS command files immediately. You'll be looking at the pieces that make up the files as you progress through the lesson. STATS command file:. This command file lets you check the number of jobs on the system and compare them to the current job limit. If the number of jobs has approached the limit (anything over three less than the job limit), the command file tells you not to stream the job. ECHO *** CURRENT JOBS = !HPJOBCOUNT ECHO *** CURRENT JOB LIMIT = !HPJOBLIMIT IF HPJOBCOUNT<=HPJOBLIMIT-3 ECHO *** NUMBER OF JOBS IS STILL REASONABLE --- STREAM JOB NOW *** ELSE ECHO *** APPROACHING JOB LIMIT --- STREAM JOB LATER *** ENDIF LF command file:. This command file lets you list the names and characteristics of all files in a specified group and account, using LISTFILE,1 or LISTFILE,2 or LISTFILE,3 commands. SETVAR FILENAME,"//" SETVAR RESPONSE,"N" SETVAR OPTION,"1" INPUT RESPONSE;PROMPT="DO YOU WISH TO LIST ANY FILE(S)? (Y OR N): " WHILE RESPONSE='Y' DO INPUT FILENAME;PROMPT="ENTER FILE.GROUP.ACCT (@ ALLOWED,// TO END): " IF FILENAME <> '//' THEN INPUT OPTION;PROMPT="ENTER LISTFILE OPTION (1,2,3): " LISTFILE !FILENAME,!OPTION ELSE SETVAR RESPONSE,'N' ENDIF ENDWHILE DELETEVAR FILENAME,RESPONSE,OPTION Assigning and displaying variable values Now that you have had a chance to look at the command files, you'll be examining the variables within them. An MPE/iX variable is just like a programming variable. It is a placeholder that appears in command syntax. When the actual command is entered, a value is specified to replace the placeholder. To define (create) a variable, only a SETVAR statement is required: SETVAR var_name,var_value To display the variable value, all that is required is a SHOWVAR statement: SHOWVAR var_name
NOTE There are other ways to display a variable's value, but the SHOWVAR command suffices for this lesson.
NOTE For Programmers Unlike a programming variable, an MPE/iX variable is declared and assigned a value in one step. No type statement is required, since the variable type is automatically defined when the value is assigned. An exception to this rule is that any variable used with the INPUT command is considered type string, regardless of the value that it contains.
To demonstrate the ease of assigning and displaying values, enter the following statements: x = your user number SETVAR USER,"USERx" SETVAR GROUP,"CLASS" SETVAR ACCT,"ACCTx" SHOWVAR USER,GROUP,ACCT You should see the following: USER = USERx GROUP = CLASS ACCT = ACCTx
NOTE Either single or double quotation marks may be used. In special cases, you must use double quotes. For example, you may wish to use a single quotation mark within a character string: SETVAR WHEN,"The meeting's at 8:00" Also, the variable name and value hmay be separated by a space or a comma: SETVAR WHEN,"The meeting's at 8:00" or SETVAR WHEN "The meeting's at 8:00"
Here are some simple examples of assigning variable values in the command files: The STATS command file makes reference to a variable called HPJOBLIMIT. The value of this variable is the number of jobs (job limit) that can run at one time. This is the same value that you see as JLIMIT when you do a SHOWJOB. This is a system-defined variable which happens to be read only. Its initial value is set by the LIMIT command. This value can be changed only by the operator or system manager at the system console. The LF command file creates and references several variables, one of which is RESPONSE. It is a user-defined variable that refers to an answer that the user must make to a specific prompt. Near the end of the file, it is automatically set to N (No): SETVAR RESPONSE "N"
NOTE Notice also, that three of the variables are assigned initial values at the beginning of the file, just in case the variables already exist and have some other values. This is a good programming practice. Text values for variables require quotation marks around them; integer values require that you do not use quotation marks.
Variable names Regardless of how it is defined, a variable must have a name that follows standard naming conventions: * begin with an alpha character or an underscore (_) * may contain 1 to 255 alphanumeric characters (including an underscore) Examples of valid names are: PACIFIC_TIME A _007 NUM_array employee1 HPSESLIMIT HPJOBCOUNT Examples of invalid names are: #$%& MAX# ERROR_# error flag 123 If you look in the two command files, you will see these variables: STATS file: LF file: HPJOBLIMIT RESPONSE HPJOBCOUNT FILENAME OPTION -------------------------------------------------------------------------------------------- | | | Q6-1 Which of the following are acceptable names for variables? | | | | | | a. $DOLLARS | | | | b. CIERROR | | | | c. FRED_FLINTSTONE | | | | d. HPINPRI | | | | e. RINGO* | | | | f. _JAMES_BOND | | | | g. VARIABLE-1 | | | -------------------------------------------------------------------------------------------- Variable types The value assigned to the variable determines the variable type, as follows: * string value is a sequence of characters or digits surrounded by quotation marks. Example: SETVAR MOVIE "FANTASIA" SETVAR DATE,"1988" * integer value is a sequence of digits preceded by +, -, $, %, or nothing. Example: SETVAR TEMP,-20 SETVAR STOCK_DIF,+30 SETVAR SALARY,100000 * hexadecimal integers are preceded by $. Example: SETVAR DEGREES_F,$D4 * octal integers are preceded by %. Example: SETVAR FLAVORS,%37 _________________________________________________________________ NOTE Variables cannot have real number values. For example, 100000 is an acceptable value for the SALARY variable because it is an integer value. 100000.00 is not an acceptable value for the SALARY variable because it is a real value. Decimal points are not allowed in any numeric variable value. _________________________________________________________________ * boolean value is TRUE or FALSE. Example: SETVAR RESPONSE,TRUE -------------------------------------------------------------------------------------------- | | | Q6-2 According to the values assigned them (by the user or the system), what are | | the types of the following variables? | | | | HPJOBLIMIT (number of jobs allowed to run): | | | | HPJOBCOUNT (number of jobs currently running): | | | | RESPONSE (user response - either Y or N): | | | | FILENAME (user-supplied file name): | | | -------------------------------------------------------------------------------------------- There are two classes of variables: * System-defined variables are generally used to store system-assigned information. (These are used in the STATS command file. All but two of them begin with the letters "HP".) * User-defined variables are generally used to store user-assigned information. (These are used in the LF command file.) The variables in both classes can be of any of the three types mentioned earlier. System-defined variables System-defined variables are variables whose names are predefined by the system, following the standard naming conventions. In general, system-defined variables are "read only," having values that are assigned and modified only by the system or system manager. Their initial values are set during system configuration and can be changed only at the system console, using special commands. Values of a few system-defined variables can be modified by a user for that user's session. Some of the more useful system-defined variables are shown below. A comprehensive list appears in appendix A of the MPE/iX Commands Reference Manual Volumes 1 and 2 (32650-90003 and 32650-90364), indicating whether such a variable is read only (not modifiable) or read/write (modifiable). The same information is available in the online Help facility. Enter HELP VARIABLESReturn to see the information on system-defined variables. Variable Read only? Read/Write? HPJOBLIMIT YES NO HPSESLIMIT YES NO HPPROMPT NO YES HPPATH NO YES HPVERSION YES NO HPUSER YES NO HPSESCOUNT YES NO -------------------------------------------------------------------------------------------- | | | Q6-3 Use the Help facility to look up each of these variables. What do each of | | these variables do? What are their current values? | | | | Hint: Use SHOWVAR to display the value of each. | | | | | | HPJOBLIMIT = | | | | HPSESLIMIT = | | | | HPPROMPT = | | | | HPPATH = | | | | HPVERSION = | | | | HPUSER = | | | | HPSESCOUNT = | | | | Q6-4 How could you list all of the system-defined and user-defined variables? | | | | Hint: Use a "wildcard" character in the same manner that you did when | | listing files or users/accounts/groups. | | | -------------------------------------------------------------------------------------------- To illustrate the use of SETVAR with a modifiable, system-defined variable, please enter the commands as shown in this example: Example: Suppose that that you want to change the prompt to "Hi There: ". You can change the value of the system-defined variable, HPPROMPT, by entering: SETVAR HPPROMPT,"Hi There: " Do this now. Press RETURN. You should see the new prompt. The new prompt remains in effect until you log off. You modify it later. Use the SHOWVAR command to verify the value of the current prompt: SHOWVAR HPPROMPT Use the SHOWVAR command again to determine your current capabilities: SHOWVAR HPUSERCAPF Your capabilities should be AM, IA, BA, ND, SF, and PH. -------------------------------------------------------------------------------------------- | | | Q6-5 What are the system-defined variables in the STATS command file? | | | | Q6-6 Are those variables user-modifiable? | | | -------------------------------------------------------------------------------------------- User-defined variables User-defined variables are variables with names and values that the user specifies. Once again, names must follow standard conventions. You can read, modify, or delete any user-defined variable. User-defined variables are session dependent. They are good only for the one user during that one session. They remain as long as the user who created them does not log off. They remain even if the user changes groups using the CHGROUP command. Enter this command: CHGROUP PUB What prompt do you get? Yes, it remains the same even when you change groups.
NOTE You can also use CG to perform a CHGROUP. It is a UDC works as long as MYUDC3 is one of your cataloged UDC files.
Return to the CLASS group: CG CLASS -------------------------------------------------------------------------------------------- | | | Q6-7 In the LF command file, what are the three user-defined variables? | | | -------------------------------------------------------------------------------------------- Deleting variables To delete any user-defined variable and its value, you need only issue the DELETEVAR command: DELETEVAR variable_name You cannot, however, delete any system-defined variable. Its value may be changed, but its definition remains the same. To illustrate this, delete the variables that you defined earlier: DELETEVAR USER,GROUP,ACCT Now use SHOWVAR to verify that they are gone. SHOWVAR USER,GROUP,ACCT You should get error messages indicating that the variables do not exist. Now try to do the same with these system-defined variables: DELETEVAR HPPROMPT,HPJOBLIMIT,HPSESLIMIT What message do you get? _______________________________________ | | | | | VARIABLE IS NOT DELETABLE | | | _______________________________________ Exercise 6-1: variables. 1. Define a variable called MYPROMPT and assign it the value currently stored in HPPROMPT. 2. Display the value of MYPROMPT. 3. Delete MYPROMPT. Verify that it is gone. Try to delete HPPROMPT. Why can you delete MYPROMPT, but not HPPROMPT? ********** End of Exercise 6-1 ********** Lesson summary 1. System-defined variables have system-assigned names and values. Some of them have values that can be modified by the system manager. A few of them can be modified by the user. 2. User-defined variables have user-defined names and values. 3. SHOWVAR and SETVAR are used to display and assign variable names and values. 4. DELETEVAR deletes a specified user-defined variable and its value.