style-guide: add guidelines for standard streams; fix remaining pages (#11196)

* readonly, {un,}compress, zbarcam: use proper syntax for IO streams

* style-guide: add guidelines for standard streams

* duckdb, perl: add backticks around stdin and stdout

pages/common/duckdb.md

@@ -27,7 +27,7 @@
 
 `duckdb {{path/to/dbfile}} -init {{path/to/script.sql}}`
 
-- Read CSV from stdin and write CSV to stdout:
+- Read CSV from `stdin` and write CSV to `stdout`:
 
 `cat {{path/to/source.csv}} | duckdb -c "{{COPY (FROM read_csv_auto('/dev/stdin')) TO '/dev/stdout' WITH (FORMAT CSV, HEADER)}}"`
 

pages/common/perl.md

@@ -3,7 +3,7 @@
 > The Perl 5 language interpreter.
 > More information: <https://www.perl.org>.
 
-- Print lines from stdin [m/] matching regex1 and case insensitive [/i] regex2:
+- Print lines from `stdin` [m/] matching regex1 and case insensitive [/i] regex2:
 
 `perl -n -e 'print if m/{{regex1}}/ and m/{{regex2}}/i'`
 

pages/common/readonly.md

@@ -12,6 +12,6 @@
 
 `readonly {{existing_variable}}`
 
-- [p]rint to the standard output the names and values of all read-only variables:
+- [p]rint the names and values of all read-only variables to `stdout`:
 
 `readonly -p`