Hacking Google Maps and Google Earth (ExtremeTech)

68 Part I — Basics

Reading Delimited Files

Getting information out of a delimited file is generally straightforward, although there are a

few oddities that can complicate matters. If the file is tab-delimited or uses some other delimit-

ing character (colons, semicolons, and tildes [~] are common), fields are delimited by tabs and

records are delimited by a carriage return and/or a linefeed character. To read the data, you read

each line and split the line up by tabs to extract the individual fields.

Listing 5-1 shows an example of this technique in action with a Perl script. Most languages

have some form of tokenizer (a function that converts lines according to a separation character

or expression) that will split up the string on a given character; here, I use the split function to

extract each field from the record.

Listing 5-1:Reading a Delimited File

open(DATA,$ARGV[0]) or die “Cannot open file: $!”;

while(<DATA>)

{

chomp;

my ($id,$ref,$fname,$lname,$country) = split /\t/,$record;

print “ID: $id\nRef: $ref\nFirst: $fname\nLast: $lname\nCountry:

$country\n”;

}

close(DATA);

For comma-separated value (CSV ) files, the process is slightly more complicated because a

value in a CSV file is normally additionally qualified with double quotes to ensure that any

data that may include a comma is not misunderstood during parsing. Although you could

develop such a solution yourself, it’s easier to use an existing module. In this case, I use the

Text::CSV_XSmodule to do the parsing. Listing 5-2 shows an example of an application in

action.

Listing 5-2:Reading a Comma-Separated Value File

use Text::CSV_XS;

open(DATA,$ARGV[0]) or die “Couldn’t open file: $!”;

my $csv = Text::CSV_XS->new();

while(<DATA>)

{