`` backquotes

use `` to get the output of the command. use chomp to delete the new line of the output.

chomp(my $no_newline_now = `date`);
print "A moment ago, it was $no_newline_now, I think.\n";

my @functions = qw /int rand sleep length hex eof not exit sqrt umask/;
my %re;

foreach (@functions){
    $re{$_} = `perldoc -t -f $_`;
}

foreach my $key (keys %re){
    print  $re{$key};
}

my $who_text = `who`;
the outputs are now in one string, include some newlines.
my @who_list = `who`;
the every line is the element of array who_list. every element includes a newline.