Read a file into an array using Perl

Question

I am currently reading a file and storing the data in an array named @lines. Then, I loop through this array using a for loop and inside the loop I match on certain values:

$find = "fever";

if ($_ =~ /$find/) {
    print "$_\n";
    $number++;
    #@lines =
    #print ("there are : " . $number);
}

At the moment, I am using a scalar, $find, with a value of fever instead of performing the repetitive statements for each filter.

Can I pass an array for comparison instead of a scalar keyword?

Answer 1

If you read a file into a list it will take everything at once

@array = <$fh>;  # Reads all lines into array

Contrast this with reading into a scalar context

$singleLine = <$fh>;  # Reads just one line

Reading the whole file at once can be a problem, but you get the idea.

Then you can use grep to filter your array.

@filteredArray = grep /fever/, @array;

Then you can get the count of filtered lines using scalar, which forces scalar (that is, single value) context on the interpretation of the array, in this case returning a count.

print scalar @filteredArray;

Putting it all together...

C:\temp>cat test.pl
use strict; use warnings;  # always

my @a=<DATA>;  # Read all lines from __DATA__

my @f = grep /fever/, @a;  # Get just the fevered lines

print "Filtered lines = ", scalar @f;  # Print how many filtered lines we got

__DATA__
abc
fevered
frier
forever
111fever111
abc

C:\temp>test.pl
Filtered lines = 2
C:\temp>

Answer 2

If you have Perl 5.10 or later, you can use smart matching (~~) :

my @patterns = (qr/foo/, qr/bar/);

if ($line ~~ @patterns) {
    print "matched\n";  
}