Programming the Perl DBI

Querying Data

Since delimited files are a very low-level form of storage manager, any manipulations that we wish to perform on the data must be done using operating system functions and low-level query logic, such as basic string comparisons. The following program illustrates how we can open a data file containing colon-separated records of megalith data, search for a given site, and return the data if found:

#!/usr/bin/perl -w # # ch02/scanmegadata/scanmegadata: Scans the given megalith data file for # a given site. Uses colon-separated data. # ### Check the user has supplied an argument for ### 1) The name of the file containing the data ### 2) The name of the site to search for die "Usage: scanmegadata <data file> <site name>\n" unless @ARGV == 2; my $megalithFile = $ARGV[0]; my $siteName = $ARGV[1]; ### Open the data file for reading, and die upon failure open MEGADATA, "<$megalithFile" or die "Can't open $megalithFile: $!\n"; ### Declare our row field variables my ( $name, $location, $mapref, $type, $description ); ### Declare our 'record found' flag my $found; ### Scan through all the entries for the desired site while ( <MEGADATA> ) { ### Remove the newline that acts as a records delimiter chop; ### Break up the record data into separate fields ( $name, $location, $mapref, $type, $description ) = split( /:/, $_ ); ### Test the sitename against the record's name if ( $name eq $siteName ) { $found = $.; # $. holds current line number in file last; } } ### If we did find the ...