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/linux/compress.md

@@ -15,7 +15,7 @@
 
 `compress -b {{bits}}`
 
-- Write to standard output (no files are changed):
+- Write to `stdout` (no files are changed):
 
 `compress -c {{path/to/file}}`
 

pages/linux/uncompress.md

@@ -11,10 +11,10 @@
 
 `uncompress -f {{path/to/file1.Z path/to/file2.Z ...}}`
 
-- Write to standard output (no files are changed and no `.Z` files are created):
+- Write to `stdout` (no files are changed and no `.Z` files are created):
 
 `uncompress -c {{path/to/file1.Z path/to/file2.Z ...}}`
 
-- Verbose mode (write to standard error about percentage reduction or expansion):
+- Verbose mode (write to `stderr` about percentage reduction or expansion):
 
 `uncompress -v {{path/to/file1.Z path/to/file2.Z ...}}`

pages/linux/zbarcam.md

@@ -1,9 +1,9 @@
 # zbarcam
 
-> Scans and decodes barcodes (and QR codes) from a video device.
+> Scan and decode barcodes (and QR codes) from a video device.
 > More information: <https://manned.org/zbarcam>.
 
-- Continuously read barcodes and print them to standard output:
+- Continuously read barcodes and print them to `stdout`:
 
 `zbarcam`