HP 3000 Manuals HP 3000 Manuals
DEBLOCK
Lets you deblock blocked records. For example, you can use DEBLOCK to
make smaller records from larger ones or to copy files from systems with
records that are not aligned on two-byte word boundaries.
Syntax
;DEBLOCK=logical-record-length
Where:
logical-record- Is a signed integer representing the length of each
length logical record in the tofile. A positive integer
represents the length in two-byte words, and a
negative integer represents the length in bytes.
Operation
DEBLOCK is principally used for copying tapes from other systems to an HP
3000 system. For more information on copying foreign tapes, refer to
chapter 3.
FCOPY assumes that each group of bytes or words you specify with DEBLOCK
is a record. FCOPY copies the record to the tofile and then aligns it on
word boundaries.
Be careful when specifying the logical-record-length. If the input
record length is not a multiple of the logical-record-length you specify,
any fractional remainder of the input record is lost. Figure 5-1
illustrates this principle.
_____________________________________________________________________
| |
| Input record: 250 bytes |
| ------ ------ ------ ------ ------ ------ |
| | 45 b | 45 b | 45 b | 45 b | 45 b | 25 b | |
| | | | | | | | |
| ------ ------ ------ ------ ------ ------ |
| |
| Logical-record-length specified as 45 bytes results in: |
| ------ ------ ------ ------ ------ ------ |
| | 45 b | | 45 b | | 45 b | | 45 b | | 45 b | | | |
| | | | | | | | | | | | | |
| ------ ------ ------ ------ ------ ------ |
| output output output output output lost |
| rec #1 rec #2 rec #3 rec #4 rec #5 25 bytes|
_____________________________________________________________________
Figure 5-1. Logical Record Length
If you deblock labeled tapes, you must specify "undefined" records in the
FILE command describing the tape file. For example:
FILE TAPEBYTE;DEV=TAPE;LABEL=TLABEL;REC=-6000,1,U,ASCII
Example
The example below copies a file from tape to disk. The original tape
file, TAPEBYTE, is a foreign tape that has records grouped in 79-byte
blocks, and its blocking factor is 10. The FILE command in the example
instructs FCOPY to treat TAPEFILE as if each block of the file were a
single record, by defining the record length as the original record
length times the blocking factor (790), and defining the new blocking
factor as 1. The FCOPY command instructs FCOPY to copy the file,
extracting 79-byte records from each block.
>:FILE TAPEBYTE;REC=-790,1,U,ASCII
>FROM=*TAPEBYTE;TO=DISC1;DEBLOCK=-79