HP 3000 Manuals HP 3000 Manuals
File Designator Enhancement:
Embedded CI Variables and Expressions by Pete Stoppani, Information
Software Division
With the introduction of MPE XL's Command Interpreter the concept of CI
variables and expressions was added to the user environment. CI
variables and expressions provide a powerful extension to MPE XL's user
interface. In order to expose the versatility and increased
expressiveness of CI variables and expressions in the file system, the
file designator options of the HPFOPEN and FOPEN intrinsics have been
enhanced to allow embedded CI variables and expressions.
EMBEDDING CI VARIABLES AND EXPRESSION
The syntax for variables and expressions embedded in file designators is
the same as for variables and expressions used at the Command Interpreter
level. To embed a variable and/or expression in a file designator one
simply precedes the variable/expression with an exclamation mark ("!" ).
The exclamation mark indicates to the intrinsic that a variable or
expression is present and that these should be evaluated (also called
'substituted') before the file designator is parsed and evaluated. By
evaluating variables before validating the file designator the file
system retains compatibility with previous versions of MPE.
WARNING Since the exclamation mark is now used to identify the existence
of embedded Command Interpreter variables and expressions, the
exclamation mark is no longer a valid FOPEN formaldesignator
terminator character.
AFFECTED FILE DESIGNATOR OPTIONS
There are several options that can be used to specify a file designator.
Each of these options may contain embedded CI variables and expressions.
HPFOPEN provides the following three file designator options:
formaldesignator (item# 2), Pascal XL string (item# 51), and file
equation string (item# 52). FOPEN provides one file designator option
called the formaldesignator option. The following sub-sections show
examples of how to specify embedded variables for each of these options.
Also, several of these file designator options have 'length' limitations
that affect the use of embedded variables, so these limitations are also
discussed below. For the following examples assume that these commands
have been executed successfully:
:SETVAR afile1 "payroll"
:SETVAR afile2 "!afile1.!!hpgroup.!!hpaccount"
:SETVAR id 1000
:SETVAR logfile "!!['log'+'!!id'+'.logfiles']"
HPFOPEN's 'formaldesignator' Option
The following Pascal/XL example opens the file 'payroll.pub' using the CI
variable 'afile1'.
formal_desig := '%!afile1.pub%';
HPFOPEN (file_number, status, 2 {formaldesignator}, formal_desig, ...);
Up to 91 characters may be passed to HPFOPEN's formaldesignator option
(including the delimiter characters). This is the only limitation for
this option.
HPFOPEN's 'Pascal XL String' Option
The following Pascal/XL example opens the file 'log1000.logfile'
using the CI variable 'logfile' which contains the expression
'!['log'+'!id'+'.logfiles]'. This example could be used to generate log
file names in a job that increments the variable 'id' each time the job
runs a program which contains the following code segment.
file_desig_string := '!logfile';
HPFOPEN (file_number, status, 51{Pascal XL String}, file_desig_string, ...);
Up to 93 characters may be passed to HPFOPEN's Pascal XL String option
(including the string size word). This is the only limitation for this
option.
HPFOPEN's 'File Equation String' Option
The following Pascal/XL example opens the file 'payroll' in the current
logon group and account using the CI variable 'afile2'.
feq_string := '%!afile2;dev=disc;rec=40,,f,ascii;disc=20000%';
HPFOPEN (file_number, status, 52 {file eq string}, feq_string, ...);
Up to 200 characters may be passed to HPFOPEN's File Equation
String option (including the delimiter characters). However, the
formaldesignator part of the file equation (to the right of the "=" when
included) has a limit of 8 characters per file name component (name,
lockword, group, account). Therefore, when embedding variables and
expressions in this option, the variables and expressions may not exceed
8 characters (including the exclamation mark). This limitation is not a
problem since a variable with a short name can be assigned an expression
which contains many characters.
FOPEN's 'formaldesignator' Option
The following Pascal/XL example opens the file 'payroll' in the current
logon group and account using the CI variable 'afile2'.
formal_desig := '!afile2%';
file_number := FOPEN (formal_desig, ...);
The formaldesignator option has a limit of 8 characters per file name
component (name, lockword, group, account). Therefore, when embedding
variables in this option, the variables may not exceed 8 characters
(including the exclamation mark). Also, only variables that consist only
of alphanumeric characters may be embedded in FOPEN's formaldesignator
option. Therefore, since expressions usually contain non-alphanumeric
characters, expressions may not be embedded in the formaldesignator
option. These limitations are not a problem since a variable with a
short name can be assigned an expression which contains many characters
(alphanumeric and non-alphanumeric).
DOCUMENTATION
Refer to the following documentation for additional information:
MPE XL Intrinsics Reference Manual (P/N 32650-60013)
MPE XL Accessing Files, Trap Handling, and Data Types Conversion Binder
Kit
MPE XL Commands Reference Manual (P/N 32650-60002)