perl: improve matching pattern example, arg consistency, etc. (#8043)

* perl: improve matching pattern examples

* perl: remove in-place find/replace sans -i'.old'

* perl: nix -0 from multiline find/replace example

* perl: update wording per code review

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: update placeholders per code review

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: update wording per code review

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: update placeholders per code review

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: update placeholders per code review

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: update placeholders per code review

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: add more -e flag markers, tweak wording

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

* perl: "print out" → "print"

Co-authored-by: Emily Grace Seville <emilyseville7cf@gmail.com>

pages/common/perl.md

@@ -19,18 +19,18 @@
 
 `perl -d {{script.pl}}`
 
-- Loo[p] over all lines of a file, editing them [i]n-place using a find/replace [e]xpression:
+- Edit all file lines [i]n-place with a specific replacement [e]xpression and save a file with a new extension:
 
-`perl -p -i -e 's/{{find}}/{{replace}}/g' {{filename}}`
+`perl -p -i'.{{extension}}' -e 's/{{regular_expression}}/{{replacement}}/g' {{path/to/file}}`
 
-- Run a find/replace expression on a file, saving the original file with a given extension:
+- Run a multi-line replacement [e]xpression on a file, and save the result in a specific file:
 
-`perl -p -i'.old' -e 's/{{find}}/{{replace}}/g' {{filename}}`
+`perl -p -e 's/{{foo\nbar}}/{{foobar}}/g' {{path/to/input_file}} > {{path/to/output_file}}`
 
-- Run a multiline find/replace expression on a file, and save the result in another file:
+- Run a regular [e]xpression on stdin, printing matching [l]ines:
 
-`perl -p0e 's/{{foo\nbar}}/{{foobar}}/g' {{input_file}} > {{output_file}}`
+`cat {{path/to/file}} | perl -n -l -e 'print if /{{regular_expression}}/'`
 
-- Run a regular expression on stdin, printing out the first capture group for each line:
+- Run a regular [e]xpression on stdin, printing only the first capture group for each matching [l]ine:
 
-`cat {{path/to/input_file}} | perl -nle 'if (/.*({{foo}}).*/) {print "$1"; last;}'`
+`cat {{path/to/file}} | perl -n -l -e 'print $1 if /{{before}}({{regular_expression}}){{after}}/'`