That only holds when 'o' and 'f' are both boolean "flags" taking no arguments. If 'f' is more like --file=x then it takes an argument. More specifically, geto

That only holds when 'o' and 'f' are both boolean "flags" taking no arguments. If 'f' is more like --file=x then it takes an argument. More specifically, getopt(3) in POSIX lets programmers very this by giving a format string. "o:f" would make your example parse as "-o" "foo" while "of:" would make it parse as "-o" "-f" "oo" and an "of" format would make it parse as you describe, "-o" "-f" "-o" "-o". ( darnir mentioned parts of this above: https://news.ycombinator.com/item?id=38968612 https://news.ycombinator.com/item?id=38968612 using the term "single character flags" to indicate no argument. ) Also, while --long-option is GNU, gcc which is perhaps the aboriginal GNU command-line utility uses single dash as in, e.g. `gcc -pipe`, though it also accepts `gcc --help`. CL syntax remains quite varied in the wild.