our ($rows, $cols);         #if use my ($rows,$cols), it will not work
no strict 'refs';                   # for ${$1}/g below
my $text;

($rows, $cols) = (24, 80);
$text = q(I am $rows high and $cols long);  # like single quotes!
$text =~ s/\$(\w+)/${$1}/g;
print $text;
#I am 24 high and 80 long

##</code><code>##

$AGE = 17;
$text = 'I am $AGE years old';      # note single quotes
$text =~ s/(\$\w+)/$1/eeg;           # print I am 17 years old
$text =~ s/(\$\w+)/$1 * 2/eegx;  #I tried to double the age, but faile
+d

##</code><code>##

$text = "I am 17 years old";
$text =~ s/(\d+)/2 * $1/eg; #now I am 34 years old