k/Column number in Perl - perl

Question

So I'm sure this is somewhere on the site, but as always, I have looked high and low before asking a question.
In Bash, you can use certain flags on some commands (such as k[number] on sort) to grab a certain column from a text file. What is the method for doing this in Perl? For an example from my input file:
Jess 6 8 25000
Say that I want to run a statement
if (k2 =< 6)
{
print "foo";
}
Of course, k2 doesn't work in Perl. May someone show me (or link me to) how this is done?

Answer 1

You can try with the command line Perl as well
with the inputs
$ cat reubens.txt
0 5 0
0 10 0
0 15 0
0 20 0
0 1 0
0 10 0
$ perl -lane ' print "The second column is ", $F[1] < 10 ? "less than 10": $F[1]==10 ? "equal to 10" : "more than 10" ' reubens.txt
The second column is less than 10
The second column is equal to 10
The second column is more than 10
The second column is more than 10
The second column is less than 10
The second column is equal to 10
$

Answer 2

In case you want to do it for exactly one column and want to avoid maintaining the result of "split" in array shape. (Otherwise use split as mentioned in the comments.)
perl -ne"/(?:\w+\s+){1}(\w+\b)/;print $1.\"\n\""
Will print the column of word-like characters between space-like characters, identified by the number inside "{}", in this case "1"; counting columns starting with 0.
E.g. it prints "6" for the input example, using "1".
How:
Make a regular expression for a column followed by space,
(?:\w+\s+)
require it a number of times,
{1}
then grab a regular expression for a colum followed by anything not word-like (including end of line)
(\w+\b)
The desired column is found in the grabbed string
$1
I did this in a command line one liner which expects standard input, to be able to test it.
Please just adapt it into your script.

Answer 3

This will check the second column:
(split)[1]
Sample script:
use strict;
use warnings;
my $filename = 'input';
open(FILE, $filename) or die "Can not open $filename.";
print "\n";
while(<FILE>)
{
#The test
if ((split)[1] < 10)
{
print "The second column is less than ten\n";
}
elsif ((split)[1] > 10)
{
print "The second column is more than ten\n";
}
else
{
print "The second column is equal to ten\n";
}
}
Input:
#Input file
0 5 0
0 10 0
0 15 0
0 20 0
0 1 0
0 10 0
Output:
The second column is less than ten
The second column is equal to ten
The second column is more than ten
The second column is more than ten
The second column is less than ten
The second column is equal to ten