Rdb: Ruby-Nachbau der MWC /rdb-Werkzeuge

man/unlock.man

@@ -0,0 +1,103 @@
+.TH unlock "" "" "/rdb Command"
+.PC "Unlock a record or field of a file"
+\fBunlock \fItableorlist processid from to indexfrom indexto\fR
+.PP
+.II table^unlock
+.II "record locking"
+The command
+.B unlock
+unlocks a record or file by removing a row from a common unlock file.
+File \fB/tmp/L\fItableorlist\fR
+contains one line for each locked record or field plus
+.I processid
+of the process that locked it.
+.I from
+and
+.I to
+give, respectively, the offsets of the beginning and end of the locked
+record or field;
+and
+.I indexfrom
+and
+.I indexto
+give, respectively, the offsets of the beginning and end of the row or
+field's entry in the secondary index file.
+.SH Example
+Let us use
+.B unlock
+on table
+.BR inventory ,
+which is 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, we use the
+.B /rdb
+command
+.B seek
+to locate the record and return the offset and size:
+.DM
+	LOCATION=`echo 5 | seek -mb inventory Item`
+.DE
+.PP
+The above command returns the offset and size of column
+.B Item
+in row 5 of table
+.BR inventory ,
+and writes the informatio into environmental variable
+.BR LOCATION .
+When we look at the contents of
+.BR LOCATION ,
+we see the following:
+.DM
+	207 245 0 8
+.DE
+.PP
+This means that the record begins 207 bytes into the file, ends
+245 bytes into the file, and therefore is 38 bytes long.
+.PP
+Now we can call
+.B unlock
+to unlock the record:
+.DM
+	unlock inventory $$ $LOCATION
+.DE
+.PP
+Note that we use the environmental variable
+.B $LOCATION
+to supply the location.
+We also use the shell's built-in variable \fB$$\fR to
+write the process identifier onto the command line.
+.PP
+Let's see what the lock file looks like.
+Since we're locking table
+.BR inventory ,
+the lock file is named
+.BR Linventory .
+If we type the command:
+.DM
+	cat /tmp/Linventory
+.DE
+.PP
+we see the message:
+.DM
+	cat: cannot open /tmp/Linventory
+.DE
+.PP
+.B unlock
+removes the lock file if it removes the last lock line.
+.SH "See Also"
+.B
+lock,
+seek
+.R
+.SO unlock