Programming the Perl DBI

Deleting Values

Deleting values is the final operation that can be performed on DBM files. Updating is as simple as assigning different values to the appropriate key within the database, and deleting is equally simple. This operation is performed by using the standard Perl delete function on the appropriate key within the database. delete removes it from the hash that represents the database, and because the hash has been tied to the DBM file, it is purged from that also.

The following program inserts three records into a Berkeley DB, and then dumps the database to show that the records are there. Following that process, a single record is deleted and the database is redumped to illustrate the deletion. Here’s the program:

#!/usr/bin/perl -w # # ch02/DBM/delete: Creates a Berkeley DB, inserts some test data then # deletes some of it use strict; use DB_File; ### Initialize the Berkeley DB my %database; tie %database, 'DB_File', "delete.dat" or die "Can't initialize database: $!\n"; ### Insert some data rows $database{'Callanish I'} = "Western Isles"; $database{'Avebury'} = "Wiltshire"; $database{'Lundin Links'} = "Fife"; ### Dump the database print "Dumping the entire database...\n"; foreach my $key ( keys %database ) { printf "%15s - %s\n", $key, $database{$key}; } print "\n"; ### Delete a row delete $database{'Avebury'}; ### Re-dump the database print "Dumping the database after deletions...\n"; foreach my $key ( keys %database ) { printf "%15s - %s\n", $key, $database{$key}; ...