wc
TextPackage: coreutils
Counts lines, words and bytes. wc -l on the output of a grep or an ls turns a list into a number — the shape a check takes in a script.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
wc -l- Counts lines.
wc -c- Counts bytes rather than lines. The form that shows a file emptied by a redirection, where
wc -lwould also print zero for a file truncated mid-line.