The correct way to read a data file into an array

Question

I have a data file, with each line having one number, like

10 20 30 40 

How do I read this file and store the data into an array?

So that I can conduct some operations on this array.

Answer 1

Just reading the file into an array, one line per element, is trivial:

open my $handle, '<', $path_to_file; chomp(my @lines = <$handle>); close $handle; 

Now the lines of the file are in the array @lines.

If you want to make sure there is error handling for open and close, do something like this (in the snipped below, we open the file in UTF-8 mode, too):

my $handle; unless (open $handle, "<:encoding(utf8)", $path_to_file) {    print STDERR "Could not open file '$path_to_file': $!\n";    # we return 'undefined', we could also 'die' or 'croak'    return undef } chomp(my @lines = <$handle>); unless (close $handle) {    # what does it mean if close yields an error and you are just reading?    print STDERR "Don't care error while closing '$path_to_file': $!\n"; }  

Answer 2

There is the easiest method, using File::Slurp module:

use File::Slurp; my @lines = read_file("filename", chomp => 1); # will chomp() each line 

If you need some validation for each line you can use grep in front of read_file.

For example, filter lines which contain only integers:

my @lines = grep { /^\d+$/ } read_file("filename", chomp => 1);