The CHECK-SUM command provides statistical information on all or specified items in a file. This information includes the total number of bytes, the average number of bytes, the number of items check-summed, the check-sum, and the bit count. Check-sums are useful for determining whether data in a file has been changed.
Format
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CHECK-SUM [DICT] filename [item-list] [attribute-name] [selection] |
Parameter(s)
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DICT |
Specifies the file dictionary. |
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filename |
Name of the file. |
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item-list |
List of item-IDs. If an item-list is not specified, all items are check-summed. |
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attribute-name |
Specifies one particular attribute. If an attribute is not specified, the D-pointer to the data file is used. If there is no default, or if the attribute marker is 9999, the entire item is included. |
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selection |
Specifies one or more conditions an item must meet to be included. For a complete description of selection expression syntax, see the LIST Command. |
Description
To use check-sums, run the CHECK-SUM command on all files or portions of files to be verified, and keep a copy of the output statistics. Whenever the CHECK-SUM command is subsequently run, compare the new check-sum to the old one. If the check-sums are identical, the items have not changed. Remember to rerun the CHECK-SUM command whenever the file is changed in any way.
The check-sum is calculated by multiplying the binary value of each character by its positional value. The product has a high probability of being unique for any given character string. The check-sum is the arithmetic total, minus overflow, of all bytes in the selected items.
When you run the CHECK-SUM command, its output is displayed in the following format:
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BYTE STATISTICS FOR filename | attribute TOTAL = bytes AVERAGE = avg-bytes ITEMS = items CKSUM = cksum BITS = count |
The CHECK-SUM display provides the following information based on the items processed:
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filename/ attribute |
Name of the file or attribute for which the statistics are produced. |
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bytes |
Total number of bytes for the element stored in the attribute or item. |
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avg-bytes |
Average number of bytes. |
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count |
Number of items check-summed. |
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cksum |
The check-sum. |
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count |
Bit count for the elements stored in the attribute or item. |
Using CHECK-SUM
The following example shows a check-sum for a file called CUSTOMERS:
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>CHECK-SUM CUSTOMERS
BYTE STATISTICS FOR : CUSTOMERS TOTAL = 119 AVERAGE = 10.81 ITEMS = 11 CKSUM = -404163063996 BITS=11
> |