+#+BEGIN_SRC fundamental :tangle ./temp/aa.txt
+ aa: 1
+ bb: 2
+ cc: 3
+ dd: 4
+#+END_SRC
+
+#+BEGIN_SRC sh :results output replace
+ perl -wnl -e 'print "==$.: $_"' ./temp/aa.txt
+#+END_SRC
+
+#+RESULTS:
+: ==1:
+: ==2: aa: 1
+: ==3: bb: 2
+: ==4: cc: 3
+: ==5: dd: 4
+
+*** Special Variable
+See special variable in perl [[http://perldoc.perl.org/perlvar.html][perlvar]], or =perldoc perlvar=
+- =$.= Current line number
+