Serving the Business Basic market best

First thing to know are the verbs, functions and parameters that are necessary to understand the search rules of PxPLUS .

'CD' parameter.
The 'CD' parameter is default 'OFF', which means the current directory is searched after the PREFIXes. If set to 'ON', PxPLUS checks the current directory before checking the PREFIX list for a file.
(see below for 'Search Rules')

You can check the value of the parameter by using : PRINT PRM('CD')
and you can set the parameter by using: SET PARAM 'CD'=1 (or 0)
 

PREFIX
You can compare the PREFIX with the PATH variable in MS-DOS or UNIX.
Use the PREFIX directive to define a series of search paths to be inserted in front of all relative file references used in OPEN / LOAD / RUN / CALL / PERFORM directives.
(PxPLUS OPENs files with absolute paths directly, without performing a search.)
Example:
PREFIX "/usr/mydir/data/ /usr/mydir/prog/ /usr/mydir/sub/ D:/other/data/"

Different paths must be separated by a space.
As you can see, you can add a drive letter before a directory, to indicate to search a different drive than specified with the SETDRIVE verb.

You can specify up to 10 differently numbered PREFIXes, i.e. PREFIX (0) through PREFIX (9).
Example:
PREFIX (0) "/usr/mydir/data/"
PREFIX (1)"/usr/mydir/prog/ /usr/mydir/sub/"
PREFIX (2)"D:/other/data/"
 

The advantage is that you can DISABLE and ENABLE a specific PREFIX.
i.e.: DISABLE 2, disables the search in D:/other/data/.

PREFIX (0) " … " is the same as PREFIX " … "

If you need to include a space within a directory name, then that directory location must be enclosed in double quotation marks.
For example:
PREFIX "C:/Tmp/ C:/usr/ ""C:/Program Files/"""

PRINT PFX or PRINT PFX (n) prints the value of the PREFIX.
 

EQUALS signs for special matching.
Equals signs in your PREFIX have special meaning. Each character of the filename that corresponds by position to an equals sign will be used to form a subdirectory name to be used in the search. For instance, if you include 1 equals sign, PxPLUS will interpret that to mean that the first character of your filename is also the subdirectory name. If you include 2 equals signs, it will take the first 2 characters as matching the subdirectory name, and so on.
The purpose was to split up large directories, inherited from other Business Basics, into smaller ones for faster access and better management.

Example:
Suppose your application consists of more than one module. The program name indicates to which module they belong. i.e. GL001 GL002 GL003 belong to the module 'General Ledger' and AR001 AR002 … belong to the module 'Account Receivable'. Then you can split your directory into separate subdirectories. The name of these subdirectories must be the same as the first corresponding characters of the module, in our example GL and AR.
When looking for a program or file, PxPLUS evaluates the initial two characters as matching characters and uses them as the name of the subdirectory where the search will commence for relative file references.
For example:
PREFIX "/myapp/==/"
OPEN (1)"ARHIST"
PxPLUS evaluates the filename 'ARHIST as /myapp/AR/ARHIST for purposes of the initial search.

Asterisks as PREFIX Wild Cards.
You can also use * and ** as wild-card characters to support the use of filename extensions without modifying your code. This feature was added to the PxPLUS language as of Ver. 4.20 primarily for WINDOWS 2000 users, since the Microsoft Certification rules for WINDOWS 2000 require that all files have file extensions. With the wild-card characters, you can rename your files on disk with a common file extension without modifying your program code.

Using a single asterisk (*):
If your PREFIX directive includes an asterisk plus a specified extension as a filename, PxPLUS inserts the filename from your OPEN command in place of the asterisk and searches first for your filename with the extension you specify in the PREFIX.
For example:
PREFIX "/mydir/*.dat"
OPEN(1)"customer"
PxPLUS will scan the disk for "/mydir/customer.dat" and OPEN that file if found. If 'customer.dat' is not found, PxPLUS will attempt to find and OPEN a file named "customer".

Note!
KEYED "abcde",5 will not create a file named "abcde.dat" , but
ERASE "abcde" will erase a file named "abcde.dat" !

Using two asterisks (**):
If your PREFIX directive includes two asterisks plus a specified extension as a filename, the substitution described above for a single star will occur only if your OPEN directive includes a simple filename (i.e., a filename without an extension). If your filename is complex (e.g. customer.hist), no substitution occurs.
For example:
PREFIX "/mydir/**.dat"
OPEN(1)"customer"
OPEN(2)"customer.hist"
Since OPEN (1)"customer" contains a simple filename, PxPLUS will look first for "/mydir/customer.dat", then, if not found, for "customer".
Since 'customer.hist' is a complex filename and two stars are used in the PREFIX filename, PxPLUS doesn’t add a .dat extension to customer.hist when it executes the search to find and OPEN the file.
 

PREFIX PROGRAM
Use the PREFIX PROGRAM format to define the search location(s) PxPLUS will search first when it attempts to LOAD, RUN, CALL, PERFORM or SAVE programs.
For example:
PREFIX PROGRAM "/pvx/mydir/pgm/"

to examine this prefix :
PRINT PFX(PGN)
 

PREFIX FILE
This is not the counterpart of PREFIX PROGRAM !

Use the PREFIX FILE format to do dynamic translations of filenames in your applications by defining a KEYED file as a lookup table. Any file you define as a PREFIX FILE must be a variable-length KEYED file or PxPLUS returns an Error #17: Invalid file type or contents.

If you define a PREFIX FILE, then PxPLUS searches this special KEYED file for a search location whenever it encounters an OPEN command with a relative filename, using the filename in your OPEN directive as the key to the PREFIX FILE. (Reminder: PxPLUS OPENs filenames with absolute paths directly, without performing a search.) The normal PREFIX search rules still apply after a filename has been located in the PREFIX FILE.

When you write to this special KEYED file, treat the filename from your program’s OPEN command as the KEY. The data record for each key contains the true filename you want opened instead. (PxPLUS retrieves the data record internally with a READ RECORD.)

Example:
KEYED "fileprefix.dat",25
OPEN(1)"fileprefix.dat"
WRITE RECORD(1,key="customer")"[odb]ACCESS;CUST;KEY=CUSTNO"
CLOSE(1)
……
PREFIX FILE "fileprefix.dat"
OPEN(1)"customer" ! Internally this becomes
>> OPEN(1)"[odb]ACCESS;CUST;KEY=CUSTNO"

So you don't have to change anything in your programming code, to alter your type of database. You only have to prepare the keyed file from the PREFIX FILE.

As of version 4.23, a second field is allowed in the keyed file for PREFIX FILE. This is an OPTIONS field. These OPTIONS are put into the OPT= for the OPEN of the real path/filename. The above enhancement allows an OPT= on the original OPEN, where the additional OPT= is appended to any of the options from the second field of the PREFIX FILE record.

Example:
PREFIX FILE contains the following:
Key="GLMAST", DATA RECORD="[ODB]DSN;TABLE"+sep+"KEY=field1"

If you OPEN(chan)"GLMAST"
internally PxPLUS will:
OPEN(chan,OPT="KEY=field1")"[ODB]DSN;TABLE"

If you OPEN(chan,OPT="REC=somedata")"GLMAST"
then internally PxPLUS will:
OPEN(chan,OPT="KEY=field1;REC=somedata")"[ODB]DSN;TABLE"

You can obtain the PREFIX FILE value by using PRINT PFX(-1).
 

SEARCH RULES
The PxPLUS default is to search all prefixes, in the following order:

For OPEN directives.
1) PREFIX FILE, if set. (Replaces pathname then continues sequence)
2) Current Directory (if ’CD’ parameter is set)
3) PREFIX 0 to 9
4) PROGRAM PREFIX, if set
5) Current Directory (if ’CD’ parameter is not set)

For LOAD / RUN / CALL / PERFORM / SAVE directives.
1) PREFIX FILE if set (Replaces pathname then continues sequence)
2) Program Cache
3) Current Directory (if ’CD’ parameter is set)
4) PREFIX PROGRAM if set
5) PREFIX 0 to 9
6) Current Directory (if ’CD’ parameter is not set)

The PREFIX search rules apply not only to files being found, but also to files being created. PxPLUS creates files in the first location that is permitted by the PREFIX rules. If ’CD’ (Search Current Directory) parameter is set, then all files are created in the current directory (the first permitted location). If the ’CD’ parameter is not set, then PxPLUS creates your file in the first location permitted by the search rules above.
You can use the ENABLE and DISABLE directives to control which of the numbered prefixes PxPLUS will use in the search. (While scanning PREFIXes 0 to 9, PxPLUS ignores any PREFIX that is DISABLEd.)
Note that the initial check for PROGRAM cache checks for a match against the original file names. Thus, if you used CALL "ABCD" and you had previously loaded a program with the same name, PxPLUS would use the one in cache. This eliminates the directory searches involved, but if you have duplicate program names in your system, it is possible to get the wrong one, for instance, if you CALL "ABCD" and then change your directory / prefix and re-CALL "ABCD". If this happens for duplicate program names in your system, either clear the CACHE or don’t use it.

PERFORMANCE
Another thing you should avoid is to add the drive letter in front of the pathname if the current drive is the same as the drive letter in the PREFIX.
SETDRIVE "C:" ! mostly this is the default
PREFIX "C:/myapp/data/ C:/myapp/files/ D:/mydir/somedir/ C:/pvx/lib/"
 

Better is :
SETDRIVE "C:"
PREFIX "/myapp/data/ /myapp/files/ D:/mydir/somedir/"

First, you don't need /pvx/lib in your searchpath. Every PxPLUS utility or PxPLUS subdirectory can be found using the * prefix. i.e. CALL"*web/email"
Second, by leaving out the drive letter, PxPLUS doesn't have to check if the drive exists, and thus you'll have a big performance gain.
If possible, put the path with a different drive letter at the end of the search path.