7 Command-line argument conventions

Question 1

Command options are by convention single letters prefixed by a hyphen (“-h”). Unless followed by option parameters, single character flag options can often be concatenated:

Answer 1

$ ls -l -a -t

$ ls -lat

Question 2

GNU tools offer alternatively long option names prefixed by two hyphens (“–help”). Arguments not starting with hyphens are typically filenames, hostnames, URLs, etc.

Answer 2

$ gcc –version

$ curl –head http://www.cl.cam.ac.uk/

Question 3

–

Answer 3

The special option “–” signals in many tools that subsequent words are arguments, not options. This provides one way to access filenames starting with a hyphen:

$ rm – -i
$ rm ./-i

Question 4

”-“

Answer 4

The special filename “-” signals often that standard input/output should be used instead of a file.

Question 5

Who implements these special conventions for – and -

Answer 5

All these are conventions that most – but not all – tools implement (usually via the getopt library function), so check the respective manual first.

The shell remains ignorant of these “-” conventions!