Patent Publication Number: US-5630114-A

Title: Database management system embedded in an operating system command

Description:
BACKGROUND 
     This invention is generally related to computer database systems and more particularly to a database system that is invoked by means of an operating system command. 
     Some commands are inherent in the operating system of any computer. Typically, such commands have the advantage of simplicity, ease of entry by the user, and high speed of execution by the computer. However, operating system commands can perform only relatively simple functions and have not been suitable for more complex operations such as managing a database. 
     Some users require advanced database capabilities that can only be satisfied by, and that justify the relatively high cost of, a commercial database management system. Examples of such commercial database systems are &#34;Paradox&#34; and &#34;dBASE&#34;, manufactured by Borland International, and &#34;Access&#34;, manufactured by Microsoft Corporation. These commercial systems typically must be running in the background or sometimes even the foreground, demanding computation resources, memory resources and the like from the host computer. 
     Many computer users do not need the capabilities of a commercial database system. Such users would prefer to avoid the high purchase price of such systems as well as the demands they place on computer system resources. Accordingly, there is a need for a relatively simple and low-cost way to manage a database that uses only simple commands and that does not tie up computer system resources. 
     SUMMARY OF THE INVENTION 
     The present invention provides a database management system that is embedded in operating system commands and that takes no system resources except when performing a command. 
     In a preferred embodiment the system of the invention runs in the UNIX (&#34;UNIX&#34; is a trademark of Unix Laboratories) operating system environment. UNIX commands are used to invoke the various functions of the database. Data are stored in two complementary files: a sorted file and an unsorted file. The sorted file can be searched very rapidly by means of binary search techniques or the like. New or replacement data are added very rapidly by simply appending them to the unsorted file. When there are enough records in the unsorted file, the two files are merged into a new sorted file; this merging operation, referred to herein as &#34;maintaining&#34; the database, is preferably performed when the computer system is not otherwise busy. 
     Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a computer system of the kind in which the present invention is preferably implemented. 
     FIG. 2 depicts various programs, code, and data files that are stored in the &#34;storage&#34; portion of the computer shown in FIG. 1. 
     FIGS. 3A and 3B depict the &#34;search&#34; procedure of a database system according to the present invention. 
     FIG. 4 illustrates the &#34;does record meet other criteria&#34; procedure of FIGS. 3A and 3B. 
     FIG. 5 illustrates the &#34;create new database&#34; procedure of the database system according to the present invention. 
     FIG. 6 illustrates the &#34;delete a record&#34; procedure of the database system according to the present invention. 
     FIG. 7 illustrates the &#34;insert a new record&#34; procedure of the database system according to the present invention. 
     FIG. 8 illustrates the &#34;replace a record&#34; procedure of the database system according to the present invention. 
     FIG. 9 illustrates the &#34;print&#34; procedure of the database system according to the present invention. 
     FIG. 10 illustrates the &#34;maintain&#34; command procedure of the database system according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The database management system of the present invention is described as follows. The system is referred to herein by the term &#34;idb&#34;, which in the preferred embodiment is also used as the operating system command entered by the user when the user desires to use the database system. 
     1. General Description of idb 
     Briefly, idb is designed to act as a bridge between UNIX commands and large databases. In other words, idb is a UNIX command like grep or awk but it performs database operations such as retrieval and manipulation of records. 
     There are no costs associated with maintaining the files that idb uses. Such files are regular UNIX files that can be created and maintained either by the user or by idb itself. idb uses a record description file, a main data file that contains sorted data, and an auxiliary file that contains unsorted data. idb requires that the main data file be of fixed length to facilitate the use of fast access algorithms. Developing the record descriptor file takes less than five minutes and is accelerated if C struct is available. 
     Any functionality that is not native to idb can easily be provided to connect idb with other commands. For example, idb has a reporting mechanism that can be piped to commands such as awk to generate sophisticated reports. 
     Among the strengths of idb are the following: speed (log n) for keyed access; instant usability; zero cost of purchase; zero cost of maintenance; works with standard files (no need for overhead space); wide selection of operators (e.g. =, !=, &lt;, &lt;=, &gt;, &gt;=); special replacement operators (+, +-, +=, -=); field filtering during search; case sensitivity (optional); wild characters; interactive insertion; default values; selective output; sorting; verification of key duplication (optional); partial replacement; networked operation; and minimum training. idb does not offer multiple keys, multiple relations, rollback, or SQL interface, and it has only the char data type. Operations that involve multiple related files are better handled by a commercial database because idb has no relational capability. 
     2. Design 
     idb was designed to fill the gap between standard UNIX commands (such as cut, grep, tail, and ed) that are not suitable for database applications and commercial database management systems that must be purchased and that require computer resources and significant training of users. Accordingly, the design objectives for idb were (1) typical database functionality, (2) ease of use and (3) natural blending with the UNIX philosophy of operation. As respects the third objective, idb reads data from stdin, sends data to stdout and sends error messages to stderr. idb returns an &#34;exit&#34; status that is consistent with the operations executed. This blending is naturally obtained when the results of idb are piped to other tools to construct more powerful commands. 
     For speed of operation, idb accesses records through a binary search if the user searches on a key field (a key field is a field on which the records have previously been sorted). This access method is well known and its speed is high and predictable. Binary search offers at least two advantages. First, unlike the hashing method, there is no relation between the speed of the search and the value of the key or the size of the file. Second, unlike the b-tree method, there is no need for a previous reading of the keys. 
     A drawback of the binary search method is that the records must have been sorted before being searched. This would mean that the file would have to be re-sorted after every insertion or deletion of a record. The time needed to do all this re-sorting would more than offset the advantage of the speed gained by binary searching. To avoid the need to re-sort all the time while still gaining the speed advantage of binary searching, idb maintains an auxiliary file for receiving new records to be inserted. Each search has two phases: a fast access search of the main file using binary search techniques and a sequential search of the auxiliary file. The user can merge the auxiliary file into the main file as desired, which usually would be whenever the auxiliary file becomes larger than some specified maximum. 
     3. Operation 
     idb is invoked in the same manner as any other UNIX command. All options are specified by parameters in the command line. All &#34;sanity checking&#34; is completed before starting a transaction. One transaction is considered to be the execution of a single command. Before initiating a transaction, idb plans a resource strategy to avoid deadlocks. idb performs multiple transactions of the same kind (e.g. multiple searches or multiple insertions) one file at a time. 
     idb builds a core image of the description of a file at run time. This allows the interpretation of the same data file from different views. The record descriptor follows the syntactic rules of struct in C. For example, the command 
     
         idb -f xref -s`*` 
    
     instructs idb to read a file called xref and to send a list of all records to stdout. The file xref holds the description of the record. This record description could, for example, appear as follows: 
     
         ______________________________________                                    
struct   {                                                                
       char man.sub.-- id                                                 
                 [16];                                                    
       char qfd.sub.-- id                                                 
                 [16];                                                    
       char owner                                                         
                 [32];                                                    
       char cost [4];                                                     
       char summary                                                       
                   [36]                                                   
       } xref.sub.-- data;                                                
______________________________________                                    
 
    
     where xref --  data is the name of the file that contains the actual data. The command 
     
         idb -f xref -s `spec*` -i cost&gt;100 
    
     instructs idb to report any records having a key beginning with spec and having a cost greater than 100. 
     The above record description might appear differently to a different application. For example, in another application it might be seen as follows: 
     
         ______________________________________                                    
struct   {                                                                
       char man.sub.-- id                                                 
                 [16];                                                    
       char qfd.sub.-- id                                                 
                 [16];                                                    
       miscellaneous                                                      
                   [72];                                                  
       } xref.sub.-- data;                                                
______________________________________                                    
 
    
     4. Maintenance 
     The -m parameter is used to merge the main data file and the auxiliary file. The auxiliary file contains all new records inserted in the database subsequent to the creation of the database or to the last maintenance operation. The auxiliary file has the same name as the main data file, but with a prefix of a dot. 
     During a maintenance operation, any records that have been marked as &#34;delete&#34; are removed from the main data file. Any records that contain duplicate keys are also removed unless the -x parameter is used. Then the auxiliary file is initialized. 
     The -m parameter merges the auxiliary file into the main data file unconditionally. A variant, the -M parameter, performs the merge only if a certain number of records have been inserted into the auxiliary data file. For example, 
     
         idb -f xref -m 
    
     will merge the main and auxiliary data files unconditionally, whereas the command 
     
         idb -f xref -M 20 
    
     will do the merge only if the auxiliary file has more than 20 records. 
     The -m parameter and the variant -M are positional. If either of these parameters are inserted in the command line before one of these parameters: -a (insertion), -r or -R (replacement), -d (deletion) or -s (search), maintenance is done first and then the operation specified by the other parameter is performed. If the -m or -M parameter is inserted in the command line after one of these other parameters, the operation specified by the other parameter is done first and then maintenance is performed. 
     With the -m parameter, one can easily dump a file and construct a new one with a different key. For example, if -xref2 has the following description: 
     
         ______________________________________                                    
struct   {                                                                
       char composite                                                     
                 [32];                                                    
       miscellaneous                                                      
                   [72];                                                  
       } xref2.sub.-- data;                                               
______________________________________                                    
 
    
     then the command 
     
         idb -f xref -s`*` .linevert split. idb -f xref2 -a -m 
    
     tells the first idb to dump the contents of xref2 --  data to stdout and tells the second idb to collect those data from its stdin and build xfer2 --  data. 
     5. A Simple Application 
     Assume as an example a company that provides telephone directory assistance. A file called directory --  data holds data respecting the local residents in the following format: 
     
         ______________________________________                                    
struct   {                                                                
       char last.sub.-- name                                              
                   [16];                                                  
       char first.sub.-- name                                             
                   [16];                                                  
       char phone  [8];                                                   
       char address                                                       
                   [64];                                                  
       } directory.sub.-- data;                                           
______________________________________                                    
 
    
     A value that is too long for a field will be truncated. If a value does not completely fill a field, the remainder of the field is filled with blanks. If a value is not specified at all, the entire field is filled with blanks. 
     Search Parameter 
     The simplest command a user can issue in idb is a simple search, such as: 
     
         idb -f directory -s`*` 
    
     which would result in the same list that would be obtained by using the cat command. An example of a few entries in such a list is: 
     
         ______________________________________                                    
Aardvark Bird      369-0186  110 Meadow Lane                              
Buffalo  Bill      415-8519  2310 Prairie Dr                              
Fox      Steve     857-0100  20 Chicken Lane                              
Turtle   Elmer     964-2131  89 Emerald Isle Road                         
Weasel   Sly       237-1015  312 Daisy Field Lane                         
Wolf     Peter     674-1541  1938 Zoo Road                                
Wombat   John B.   856-3612  2400 Tanager Ave                             
Wombatty S. K.     857-1236  2379 Munchkin Street                         
Zebra    Sam       875-8900  1635 Sahara Drive                            
______________________________________                                    
 
    
     If a user wanted to retrieve the listings for all people whose last name starts with the letters &#34;Wo&#34;, the command would be: 
     
         idb -f directory -s `Wom*` 
    
     and the resulting output would be: 
     
         ______________________________________                                    
Wombat   John B.   856-3612  2400 Tanager Ave                             
Wombatty S. K.     857-1236  2379 Munchkin Street                         
______________________________________                                    
 
    
     But if the user only wanted the last name and phone number, the command would be: 
     
         idb -f directory -s `Wo*` -i last.sub.-- name -i phone 
    
     and the resulting output would be: 
     
         ______________________________________                                    
Wombat               856-3612                                             
Wombatty             857-1236                                             
______________________________________                                    
 
    
     If the same search were run, but with the further condition of retrieving only those having a prefix of 857, the command would be: 
     
         idb -f directory -s `Wo*` -i &#34;phone:857*&#34; -i last.sub.-- name -i phone 
    
     and the resulting output would be 
     
         ______________________________________                                    
       Fox           857-0100                                             
       Wombat        857-1236                                             
______________________________________                                    
 
    
     In the latter example the -i parameter was used three times. The first appearance filters the search and the second and third appearances tell idb that the output should consist of the values of the last --  name and phone fields separated by a blank. idb sends the output to stdout unless some other destination is specified. Quotation marks were used around the expression phone:857* to prevent the shell from interpreting the asterisk character. 
     Insert Parameter 
     There are several ways that records can be inserted. A raw record, for example only a last name and a phone number, is inserted by the following command: 
     
         ______________________________________                                    
idb -f directory -s `Flamingo                                             
a                         857-2035`                                       
______________________________________                                    
 
    
     which does not include a first name or an address. idb will fill the &#34;first name&#34; and &#34;address&#34; fields with blanks. 
     Items can be separated by delimiters, where a delimiter is just a metastring (that is, not part of the actual data), by the following command, where    is the delimiter: 
     
         idb -f directory -s `Gull  Albert  723-3412  958 Catalina Lane` -a -D 
    
     Delimiters may also be used to insert a partial listing, such as the listing of the preceding example, as follows: 
     
         idb -f directory -s `Flamingo    857-2035` -a -D 
    
     which as before will result in the &#34;first name&#34; and &#34;address&#34; fields containing blanks. 
     If it is desired to enter a partial listing with the data in a different order than the order of the fields in the record structure, the following command can be used: 
     
         idb of directory -s `857-2035  Flamingo` -a -D   -i phone -i last.sub.-- name 
    
     If it is desired to enter a record interactively, the command 
     
         idb -f directory -a -v 
    
     will result in the following prompt, in which the length of each field is displayed graphically: 
     last --  name?. . . 
     first --  name?. . . 
     phone?. . . 
     address?. . . 
     A partial record can be entered interactively by specifying in the command parameter which fields are to be entered: 
     
         idb -f directory -a -v -i phone-i last.sub.-- name 
    
     In response to the preceding command, idb will prompt for only the phone number and last name. The value of one field can be specified in the command line while idb prompts for other fields. For example, the command: 
     
         idb -f directory -a -v -i phone -i last.sub.-- name -i first.sub.-- name:MARY 
    
     will insert the name &#34;MARY&#34; into the first --  name field and will prompt the user for the values of the phone and last --  name fields. 
     Records can be copied out of one file, for example my --  file, for insertion into another file, for example directory, by the following command: 
     
         cat my.sub.-- file .linevert split. idb -f directory -a 
    
     or 
     
         idb-f directory-a &lt; my.sub.-- file 
    
     And a filter can be used to copy only certain records from one file to another. For example, if it is desired to copy only records in which the last name starts with &#34;S&#34;, the following command would be used: 
     
         cat my.sub.-- file .linevert split. grep &#34;S*&#34; .linevert split. idb -f directory -a 
    
     If only certain fields were to be copied, for example only last --  name and phone, the following command would be used: 
     
         cat my.sub.-- file .linevert split. idb -f directory -a -i last.sub.-- name -i phone 
    
     in which case the first --  name and address fields in directory would be filled with blanks. 
     Replacement Parameter 
     Replacement mode is similar to insertion mode. The simplest example is to change the value of one field in a record. For instance, in the telephone directory listing, to change Mr. Aardvark&#39;s first name from &#34;Bird&#34; to &#34;Fowl&#34;, the following command would be used: 
     
         idb -f directory -s Aardvark -R first.sub.-- name:Fowl 
    
     More than one replacement can be done in one command; a plurality of replacements are evaluated left-to-right. 
     A record can be entirely replaced with a different record. For example, to replace Mr. Aardvark&#39;s listing with a new listing for Mr. Jim Giraffe of 900 Tower Lane, the following command would be used: 
     
         ______________________________________                                    
idb -f directory -s Aardvark                                              
r `Giraffe  Jim      968-7203 900 Tower Lane`                             
______________________________________                                    
 
    
     Delimiters can also be used, to avoid having to indicate blank spaces, as previously described. 
     Fields can be replaced in different order than they appear in the record structure. For example, to change the phone number and first name of Mr. Aardvark from 369-0186 to 321-7347 and from Bird to Fowl, respectively, the following command may be used: 
     
         idb -f directory -s Aardvark-r `321-7347  Fowl` -a -D  -R phone -R first.sub.-- name 
    
     Delete Parameter 
     The -d parameter deletes all records found by the search argument. For example, the command 
     
         idb -f directory -s Aardvark -d 
    
     deletes Mr. Aardvark and his phone and address from the directory. 
     Case Insensitive Parameter 
     The -c parameter instructs idb to disregard case. For example, the command: 
     
         idb -f directory -s `aardvark` -c 
    
     would return all of the following records: 
     
         ______________________________________                                    
Aardvark     Bird    369-0186  110 Meadow Lane                            
AARDVARK     Sam     368-9075  220 Green Street                           
aardvark     Tom     456-7890  8527 Memory Drive                          
______________________________________                                    
 
    
     whereas the command: 
     
         idb -f directory -s `aardvark` 
    
     would return only the record: 
     
         aardvark Tom 456-7890 8527 Memory Drive 
    
     When specifying case insensitivity, it is necessary for idb to perform two binary searches of a file, one search per case of the initial character of the field being searched. This is because upper and lower case instances of the same letter are represented differently, and will appear in different locations within a file that has been sorted on that field. There may be two distinct groups of records within this sorted file, one group having all of the records beginning with the uppercase letter and the other having all of the records beginning with the lowercase letter. 
     Thus, in the above example, there may be one or more intervening record between the AARDVARK record and the aardvark record. In such an event, the first binary search will find the record group containing the Aardvark and the AARDVARK records, but will not find the aardvark record. The second search will then be required to find the aardvark record. 
     It is also possible that a binary search will find a record other than the first record in a group. In the previous example, it may be that the first binary search will find the AARDVARK record rather than finding the Aardvark record. Thus, when the binary search finds a record, it will push the record into a stack. Then, idb will perform a backwards serial search looking for those records that match the search argument and push them into the stack. The backwards serial search ends when no more records match the search argument or when the loop reaches the beginning of the file. It will then be possible to pop the stack to return the record on top of the stack. That is, in the previous example, the Aardvark record. This procedure will also be performed in instances where duplication of keys is permitted. 
     Horizontal Expand Parameter 
     The layout of records is seldom stable over time. The -y parameter allows the dynamic expansion of the file either by enlarging the size of a field or by introducing a new field. For example, to make a new entry in the above telephone directory in which the value of phone must include international dialing codes and extensions, the -y parameter can be added to an insert command as follows: 
     
         idb -f directory -s `Poodle  Jacques  011-36-3-20-10-56-42-89x1235  77 Rue du Cologne, Paris` -a -D   -y 
    
     In this example, the -y parameter will expand the phone field from 8 to 28 characters throughout the file and will modify the file description to indicate that the phone field has 28 characters. 
     The -Y parameter is similar to the -y parameter except that -Y allows for either expansion or contraction of a field. 
     Using the -y parameter to add new fields will be discussed in a subsequent paragraph. 
     Retrieving a Record That Matches a Condition 
     The -o parameter is used anytime it is desired to process only one record at a time, for example in a loop. If it is desired, say, to send a letter to all persons having an 837 prefix to their phone numbers, the following Korn Shell script could be used, including the -o parameter: 
     
         ______________________________________                                    
x=1                                                                       
o $x` user=`idb -f directory -s `837-*`                                   
do                                                                        
send.sub.-- a.sub.-- letter $user                                         
((x=x+1))                                                                 
done                                                                      
______________________________________                                    
 
    
     The variable x will take the values 1, 2, 3, . . . and idb will return the first, second, third . . . record that satisfies the condition -s `837=*`. 
     Remote Access 
     If the filename following the -f parameter includes the `@` character, idb will assume that the characters following the @ are the name of a remote host and idb will execute a remote shell on the remote host, using the parameters in the command line. For example, in response to the command: 
     
         idb -f desc@remote -s `*`&gt;result 
    
     idb will execute a search on the system named remote and will leave the output of the search in the file titled result. 
     Creation of a New Database 
     Appropriate parameters may be used to cause idb to create a new file description and database. For example, the user may cause idb to use contents of an existing file called passwd to create the following file description: 
     
         ______________________________________                                    
struct   {                                                                
       char login [8];                                                    
                      /* offset = 0 */                                    
       char pwd [13];                                                     
                    /* offset = 8 */                                      
       char uid [3];                                                      
                    /* offset = 21 */                                     
       char gid [4];                                                      
                    /* offset = 24 */                                     
       char misc [27];                                                    
                    /* offset = 28 */                                     
       char home [21];                                                    
                    /* offset = 55 */                                     
       char shell [20];                                                   
                    /* offset = 76 */                                     
       } passwd.sub.-- data                                               
                    /* record len = 96 + 1 */                             
______________________________________                                    
 
    
     by means of the following command: 
     
         idb -f passwd -i login -i pwd -i uid -i gid -i misc -i home -i shell -a -y -D: -m&lt;passwd 
    
     where the parameters have the following meanings: 
     
         ______________________________________                                    
a       a record is being added                                           
i       description of a field                                            
y       create undeclared fields                                          
D:      data will be delimited by the colon                               
m       perform maintenance after the transaction has been                
        completed                                                         
______________________________________                                    
 
    
     and stdin is redirected to read from/etc/passwd. Of course, the same result could have been obtained by piping the contents of/std/passwd into idb. 
     The user may use cat and idb to create a database called group out of the fields titled group and gid from the file passwd by means of the following command: 
     
         cat group .linevert split. cut -f1,32 -d: .linevert split. idb -f group -i group -i gid -a -y -D: -m 
    
     which results in the following data file: 
     
         ______________________________________                                    
          adm    4                                                        
          atm    21                                                       
          bin    2                                                        
          daemon 5                                                        
          guest  1044                                                     
          lp     7                                                        
          mail   6                                                        
          other  1                                                        
          root   0                                                        
          scaff  24                                                       
          sys    3                                                        
          users  20                                                       
          wizard 10                                                       
______________________________________                                    
 
    
     The two databases described above may be joined by selecting those gid&#39;s in passwd that are not referenced in group by the following commands: 
     
         idb -f passwd -s `*` -i login -I gid -D: &gt;from.sub.-- passwd 
    
     
         idb -f group -s `*` -i group -I gid -D: &gt;from.sub.-- group 
    
     
         join -1 2 -2 2 -a 2 -t: from.sub.-- passwd from.sub.-- group .linevert split. grep -v `.*:.*:.*` 
    
     where the parameters of the join command mean to take the second field from both files (1 and 2); produce a line of output for each unpairable line in the file from --  group in addition to the normal output; and use the character &#34;:&#34; as a separator. The parameter -v of the grep command means to print all lines but those that match the pattern &#34;.*:.*:.*&#34;. The idb parameters have the following meanings: -s means that the search argument is the wild-card character &#34;*&#34;; the -i parameter without an argument means that what is wanted is only the fields login and gid, not the raw record; the -I parameter is similar to -i except that the output is to be sorted by gid. The result of the above three commands is the following output: 
     
         ______________________________________                                    
0                :root                                                    
1                :other                                                   
10               :wizard                                                  
21               :atm                                                     
6                :mail                                                    
______________________________________                                    
 
    
     which means that the groups named in the output have no counterparts in passwd. 
     The following command will replace the shell of all the users that belong to the groups 4 or 20 with the default shell/bin/ksh: 
     
         idb -f passwd -s `*` -i gid:20 -I gid:4 -R shelh/bin/ksh 
    
     where the -i parameter performs a logical AND to the search argument * and the paramenter -I performs a logical OR. 
     The following command adds a new record interactively: 
     
         idb -f passwd -a -v 
    
     idb will prompt the user with the name of the field followed by a number of dots corresponding with the length of the field: 
     login?. . . 
     pdw?. . . 
     uid?. . . 
     gid?. . . 
     misc?. . . 
     home?. . . 
     shell?. . . 
     Entering &lt;CNTL/D&gt; in the first field login will stop the prompting. Entering &lt;CNTL/D&gt; in any other field will prompt for the previous field. If the -s parameter is not present in the command line, idb will assume that the new record(s) come from stdin. For example, in the command: 
     
         idb -f passwd -a 
    
     idb prompts the user with a question mark if stdin is a terminal, or idb assumes that the record(s) come from either a file or a pipe. An example of this is: 
     
         idb-f passwd-a &lt;input 
    
     
         cat input .linevert split. grep &#34;r*&#34; .linevert split. idb -f passwd -a 
    
     The following command will expand a data file to create a new field: 
     
         idb -f passwd -s `*` -y -m -i new.sub.-- field:xxxx 
    
     The -i parameter with the -y parameter instructs idb to add new --  field to the file description and to expand the entire data file with four characters (the length of the string xxxx). idb will generate a new descriptor with new --  field appended to the existing list of fields. In the case of the above file structure, the result will be: 
     
         ______________________________________                                    
struct   {                                                                
       char login [8];                                                    
                     /* offset = 0 */                                     
       char pwd [13];                                                     
                   /* offset = 8 */                                       
       char uid [3];                                                      
                   /* offset = 21 */                                      
       char gid [4];                                                      
                   /* offset = 24 */                                      
       char misc [27];                                                    
                   /* offset = 28 */                                      
       char home [21];                                                    
                   /* offset = 55 */                                      
       char shell [20];                                                   
                   /* offset = 76 */                                      
       char new.sub.-- field [4];                                         
                   /* offset = 96 */                                      
       } passwd.sub.-- data                                               
                   /* record len = 100 + 1 */                             
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     Although a specific embodiment of the invention has been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated, and various modifications and changes can be made without departing from the scope and spirit of the invention. Within the scope of the appended claims, therefore, the invention may be practiced otherwise than as specifically described and illustrated.