Perl - Learning MySQL - page 531

Every standard Perl function ends by passing back a value to the code that called it. In
fact, many functions do nothing but return a value. The open( ) function returns a
nonzero value to indicate that it succeeded in opening the file, and returns zero if it
failed. Common causes of file-access errors include mistyped filenames and insufficient
privileges to access a particular file or directory. We can use an if statement to check
for a zero value; if the file-open operation failed, we can use the die( ) function to
display an error message and stop the script:
if(!open(INPUTFILE, $ARGV[0]))
{
die("Failed opening $ARGV[0]\n");
}
This combination of an if statement and an open function is worth noting; we've pre-
viously used if on logical tests such as $Username == "Ali" , but if is flexible enough
to directly test a single value, or the result of a function such as open . We can also use
the simpler or construct to call the die( ) function if the open( ) function fails:
open(INPUTFILE, $ARGV[0])
or
die("Failed opening $ARGV[0]\n");
Save this program as readfile.pl , and then get it to read in and display the contents of
the animals.csv file:
$ ./readfile.pl animals.csv
cats,2
dogs,5
fish,3
emus,4
Instead of simply printing out the file contents, let's load them into our own data
structures and process the data. We have to remove the invisible newline at the end of
each line of the text file using the chomp( ) function, then load the contents of each line
into array elements by the location of the commas using the split( ) function. For
convenience, we assign the first value to the scalar variable $AnimalName and the second
value to the scalar variable $AnimalCount . We then use these to populate the %Animals
hash.
For example, the line:
cats,2
is split at the comma into the @AnimalData array, with:
AnimalsData[0]: cats
AnimalsData[1]: 2
and these values are assigned to the variables:
AnimalName: cats
AnimalCount: 2
The statement: