PerlでMeCab + TermExtractを使う。 TermExtractはここから。http://gensen.dl.itc.u-tokyo.ac.jp/termextract.html

ext.perl

use strict;
use warnings;
use utf8;

use Text::MeCab;
use Text::TermExtract;
use TermExtract::MeCab;
use Data::Dumper;

_extract_keyword();

sub _extract_keyword {
    my $str = "ここに文章がくる";

    my $mecab_obj = _mecab($str);
    _term($mecab_obj);
}

sub _mecab {
    my ($str) = @_;
    my $mecab = Text::MeCab->new();
    my $node = $mecab->parse($str);
    my $text = "";
    while ($node = $node->next) {
        $text .= $node->surface."\t";
        $text .= $node->feature;
        $text .= "\n";
    }
    $text .= "EOS\n";
    return { mecab_string => $text};
}

sub _term {
    my ($mecab_obj) = @_;
    my $ext = Text::TermExtract->new();
    my @array_terms;
    my $mecab_string = $mecab_obj->{'mecab_string'};

    my $term_extract = new TermExtract::MeCab;
    my @noun_list = $term_extract->get_imp_word($mecab_string, 'var');

    warn Dumper @noun_list;
}