perl: add pie example per issue #1239

pages/common/perl.md

@@ -21,3 +21,11 @@
 - Run a Perl script in debug mode, using `perldebug`:
 
 `perl -d {{script.pl}}`
+
+- Replace all occurrences of a string in a file with another string, overwriting the file in-place:
+
+`perl -p -i -e 's/{{find}}/{{replace}}/g' {{filename}}`
+
+- Same, saving an unmodified copy of the original file with a different extension:
+
+`perl -p -i'.old' -e 's/{{find}}/{{replace}}/g' {{filename}}`