How can I write a Perl script that reads from another file?

Question

I want to write a Perl Script that reads a file.txt with columns of numbers,

20  30  12
31  20  54
63  30  21
11  12  10

and do some calculatio

Answer 1

Here are suggested functions to use (see the function reference):

1. Open your file for reading: use the open function
2. Loop through each line: while (my $line = <$filehandle>)
3. Remove the trailing newline: use chomp
4. Extract the values from each line: use the split function
5. Store the values in an array: use push

To verify that your array has what you want at the end:

use Data::Dumper;
print Dumper \@vals;

UPDATE

Without giving you the entire answer (since this is homework) have a look at the sample code in each entry of the function reference.

Here's something to get you started:

open my $filehandle, '<', $filename
    or die "Couldn't open $filename";
while (my $line = <$filehandle>) {
    # do stuff with $line
}
close $filehandle;

Answer 2

Use the open command. Plenty of good examples on that page.

Answer 3

This shell one-liner multiply first col with second one :

perl -lane 'print $F[0] * $F[1]' <FILE>

EDIT: And the perl script version with your new requirements and the file with 3 cols :

#!/usr/bin/perl

use strict;
use warnings;

my (@vals, $sum, $med);

while (<>) {
    @vals = split;

    print "UNSORTED: @vals\n"; 

    #sort data points 
    @vals = sort(@vals); 
    print "SORTED: @vals\n"; #test to see if there are an even number of data points 

    if(@vals % 2 == 0) { 
        #if even then: 
        $sum = $vals[(@vals/2)-1] + $vals[(@vals/2)]; 
        $med = $sum/2; 
        print "The median value is $med\n";
    }
    else{ 
        #if odd then: 
        print "The median value is $vals[@vals/2]\n";
    } 

    print "\n";
}

You may understand what's going on instead of just cut & paste ;)

To run the script :

./script.pl file_with_cols.txt