Git Flag Syntax: why do some flags have -one dash and some have --two?

Question

I am learning Git and have been unable to find any explanation of the flag syntax.

I'm not referring to the "bare double dashes"

--

which, as we know, indicate that what follows is not an option. I'm referring to various actual flags which sometimes have one dash, and sometimes have two.

git log -2 -p -U1 --graph

What is the difference between a flag with one dash and two dashes? What does the double dash indicate?

For example, the following two flags are identical, (according to this):

-q
--quiet

Why the different number of dashes? What if I put the wrong number?

Answer 1

My understanding is that git follows the 'standard' Linux convention for flags. That is:

• one dash for 'short' flags: generally one character flags, but sometimes flags with a single character, then further characters which represent a parameter to the flag (e.g. git log -SFoo, in which Foo is a parameter to the -S flag). These flags may or may not be abbreviated forms of other, longer flags.
• Two dashes for 'long' flags: multi-character flags which are usually an English word. If these flags receive parameters, it is separated from the flag by an = sign (e.g. git log --author=Peter).

This is the 'why': it is a convention which is embedded in the Linux world. Git comes from this world, so it follows the convention. The 'two dashes for a long flag, one for a short flag' rule should guide you as to how many dashes to use for a flag.

As for why there are duplicate short and long flags, such as --quiet and -q, it's just to provide the option of either mnemonic convenience or terseness. --quiet is easier to remember, but -q is quicker to type and mentally parse if you're used to it. For instance, I type git commit -m "...blah" so frequently it would get on my nerves if I had to double the length of my command every time by entering git commit --message='...blah'.

I haven't come across any git flags which behave differently given two dashes and one dash, so generally if you enter two dashes for a one-dash flag or vice versa, nothing irreparably bad will happen, git will just complain about your flags and do nothing.

Of course, git has a vast number of commands, each with a vast number of flags, so it is possible that there are exceptions to all these rules. They should generally hold though.