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
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Where:
- logical-record-length
Is a signed
integer representing the length of each 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.
Figure 5-1 Logical Record Length
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
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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
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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
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