Commands, Args, and Flags
The Command line runs commands.
The commands reviewed in the previous section are pwd, ls, and cd.
These commands can "take" arguments, or args for short.
Args get "passed to" commands. "Passed to" is a common description for writing arguments after commands.
Args in action
Taking cd ubuntu as an example, cd is the command and ubuntu is the arg passed to the command.
ls can also take args: with the terminal at the location /, one directory "above" or "outside" of home, typing ls home will list out all contents of the home directory.
args with echo
echo is another command that is used to "print" contents to the terminal.
Typing echo water <enter> will print "water" to the terminal. in this command, the "water" word is the arg passed to echo.
Flags in action
Flags are similar to but different from args.
A similarity is that flags and args are both "passed to" a command.
A difference is that flags have a prefix of -- or - before the value whereas args do not.
Taking the ls command as an example, some flags can be passed.
Typing ls --help will print a "help"ful explanation of the ls command, including args/flags that the ls command can take.
--help is a very common flag that can be passed to many commands as a way to discover some ways of using the command.
flags with ls
ls -l will use the ls command with the -l flag.
According to the ls --help doc, the -l flag will use a long listing format. This format prints a bunch more details about each file or directory.
ls -a will use the ls command with the -h flag.
According to the ls --help doc, the -h flag will with -l and -s, print sizes like 1K 234M 2G etc..
Combining flags
Flags can be combined sometimes. With ls as an example, ls -lh works!
ls -lh is ls -l and ls -h put into one single command.
The flags are merged after the single dash.
Combining flags and params
flag and params can be combined:
ls -lh home will run ls -lh against the home directory.