Read a file into an array using Perl

问题:

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?

回答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>

回答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";  
}

回答3:

Use Tie::File. It loads the file into an array, which you can manipulate using array operations. When you untie the file, its components will be saved back in the file.

回答4:

You could also use the File::Slurp module, which is convenient.

use strict;
use warnings;
use File::Slurp 'read_file';

my $fname = shift or die 'filename!';
my @lines = grep /fever/, read_file $fname; # grep with regular expression
print @lines;

If you're new to Perl, take a look at the map and grep operators, which are handy for processing lists.

Also, take a look at the ack utility, which is a great replacement for find/grep. (Actually, it's a superior alternative.)