Rdb: Ruby-Nachbau der MWC /rdb-Werkzeuge

man/lock.man

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+.TH lock "" "" "/rdb Command"
+.PC "Lock a record or field of a file"
+\fBlock \fIfilename processid from to indexfrom indexto\fR
+.PP
+.II "record locking"
+The command
+.B lock
+locks
+.I filename
+by writing a row into the lock file \fB/tmp/L\fIfilename\fR,
+which contains one line for each locked record or field.
+Its command line contains the following arguments:
+.IP \fIprocessid\fR
+The process identifier of the program that locks
+.IR filename .
+.IP \fIfrom\fR
+The beginning point of the bytes to be locked.
+.IP \fIto\fR
+The end point of the bytes to be locked.
+.IP \fIindexbegin\fR
+The beginning point of the index entry for the data being locked.
+.IP \fIindexend\fR
+The end point of the index entry for the data being locked.
+.PP
+When a process attempts to lock a string of bytes that is already locked,
+.B lock
+returns an error condition.
+You can test for this by using the COHERENT command
+.B test
+to test the shell variable \fB$?\fR.
+.SH Example
+Let's use
+.B lock
+on table
+.BR inventory ,
+which appears as follows:
+.DM
+Item    Amount  Cost    Value   Description   
+----    ------  ----    -----   --------------
+   1         3    50      150   rubber gloves
+   2       100     5      500   test tubes
+   3         5    80      400   clamps
+   4        23    19      437   plates
+   5        99    24     2376   cleaning cloth
+   6        89   147    13083   bunsen burners
+   7         5   175      875   scales
+.DE
+.PP
+First, use
+.B seek
+to locate the record and return the offset and size, as follows:
+.DM
+	LOCATION=`echo 5 | seek -mb inventory Item`
+	echo $LOCATION
+	207 245 0 8
+.DE
+.PP
+This means that the record is offset 207 bytes into file
+.BR inventory ,
+and that it is 38 bytes long, ending at byte 245.
+The 0 and 8 mean that there is no secondary index file.
+.PP
+Now we can call
+.B lock
+to lock the record:
+.DM
+	lock inventory $$ $LOCATION
+.DE
+.PP
+Note that we use the shell variable
+.B $LOCATION
+to supply the arguments
+.I from
+and
+.IR to .
+We also use the built-in shell variable \fB$$\fR to
+write the process identifier on the command line.
+.PP
+The lock
+.B /tmp/Linventory
+has the following contents:
+.DM
+	207 245 0 8
+.DE
+.SH "See Also"
+.B
+seek,
+unlock
+.R
+.br
+COHERENT Lexicon:
+.B
+test
+.R
+.SO lock