Let's say I want to search a file for a string that begins with a dash, say "-something":
grep "-something" filename.txt This throws an error, however, because grep and other executables, as well as built-ins, all want to treat this as a command-line switch that they don't recognize. Is there a way to prevent this from happening?
For grep use -e to mark regex patterns:
grep -e "-something" filename.txt For general built-ins use --, in many utilities it marks "end of options" (but not in GNU grep).
grep -- "-something" filename.txt would have worked as well (due to GNU grep's first synopsis form), but since there is a -e option for giving an expression, it might be better to use that. For grep you can also change the regexp so it doesn't actually begin with hyphen, by using a trivial character list:
grep '[-]something' This trick^Wmethod was traditionally used to avoid false matches in ps:
ps -f | grep myprog # lists both the process(es) running myprog AND the grep process # making it harder to do things like choose the right process to kill(1) ps -f | grep '[m]yprog' # lists only the 'real' processes because [m]yprog matches "myprog" # but [m]yprog does NOT match "grep [m]yprog" but in the modern era just using pgrep (or pkill) is easier.
--?--, there are exceptions (see here). The-eswitch is also mentioned in the comments section. I flagged this Q as duplicate, because I (still) think it is. You asked for a generic way and the--is a common way to handle such arguments. But that doesn't necessarily mean that this is the only way.