Suppose you’re looking for instances of -42 in a file foo.
txt.
The command grep -42 foo.
txt won’t work.
Instead you’ll get a warning message like the following.
Usage: grep [OPTION].
PATTERN [FILE].
Try grep –help for more information.
Putting single or double quotes around -42 won’t help.
The problem is that grep interprets 42 as a command line option, and.. More details