/ 
MVS-VBFile-0.03
River stage zero No dependents
/ MVS::VBFile

NAME

MVS::VBFile - Perl extension to read variable blocked files from MVS

SYNOPSIS

use MVS::VBFile;
$next_record = vbget(*FILEHANDLE);
@whole_enchilada = vbget(*FILEHANDLE);

DESCRIPTION

This module provides a single function, vbget(), to get records from a mainframe MVS file in variable blocked (VB) format. It works like the angle operator: when called in scalar context, it returns the next record; when in array context, it returns the entire file in a single array. The file must be in "binary" format (no translation of bytes) and include record descriptor words. The file may include block descriptor words but need not.

The rationale behind this is as follows. Most files from MVS systems are either fixed-length (record format FB) or variable-length (recfm VB). Perl can read fixed-length mainframe files just as it reads other fixed-length files -- open, read a certain number of bytes, close -- but variable-length files require some special handling. Since Perl provides open and close, the only function needed is one to get the next record.

Read the file as follows:

open FILEHANDLE, "..name..";
while (vbget(*FILEHANDLE)) {  # Be sure to use '*'!!
   # process and reality...
}
# OR do this:
@much_in_little = vbget(*FILEHANDLE);
# and then process the array (only on small files, of course).
close FILEHANDLE;

VARIABLE

The variable MVS::VBFile::bdws tells the module whether the file to be read contains block descriptor words. The default is 0 (false); set it to 1 or any other true value if the file contains BDW's.

RESTRICTIONS

VB (blocked) and V (unblocked) formats are supported. This function will not work properly on format VBS (spanned). Since VB is by far the most commonly used format, this should not be a major snag.

MORE ABOUT DESCRIPTOR WORDS

Record descriptor words are 4 bytes that appear at the beginning of each record in a VB file. The first two bytes contain the record length in binary (16 bits, signed, big-endian); the last two are used only by spanned records and are ignored by this module. Block descriptor words, likewise, are 4 bytes that appear at the beginning of each block, having the same format.

My experience with FTP from MVS is limited, but it seems that if you transfer a file from an MVS host via FTP including the RDW's, the RDW's will be transferred but the BDW's will not. Most applications do not require BDW's, but if you want them, they can be transferred by converting the VB file to undefined records (recfm=U) under MVS and then transferring the converted file.

AUTHOR

W. Geoffrey Rommel, grommel@sears.com, March 1999.