If you want to do this with regex, you can use the following code.

$line = "{chart {{1 {{title title_1} {xlable X-lab} {ylable Y-lab} {de
+scription desc1} {type line} {series {{1 {{x_data {1 2 3 4 5}} {y_dat
+a {20 90 60 50 30}}}}}}}}}}";


$line =~ /x_data\s+\{(.*?)\}/;
print "X DATA : $1 \n";

$line =~ /y_data\s+\{(.*?)\}/;

print "Y DATA : $1 \n";
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UPDATE: Enclose the matching expression within if block.

  if ($line =~ /x_data\s+\{(.*?)\}/) {
       print "X DATA : $1 \n";
  }
  if ($line =~ /y_data\s+\{(.*?)\}/) {
       print "Y DATA : $1 \n";
  }
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