What are Unix options (flags)?
options (also called flags) are generally single characters which in some way modify the action of the command. There may be no options or there may be several acting on the same command.
Options are preceded by a hyphen character ( - ) but there is no consistent rule among Unix commands as to how options should be grouped. Some commands allow a list of options with just a single hyphen at the beginning of the list (e.g. -apfg). Other commands require that each option is introduced by its own hyphen (e.g. -a -p -f -g)
Some options allow a value, often a filename, to be given following the option. Again, there is no consistent manner in which this is allowed, with some options requiring the value to be placed immediately following the option letter, while others expecting a space between the option letter and the value.
Unix is case-sensitive throughout. The exact combination of upper and lower case letters used in a command, option or filename is important.
For example, the options
-P in the same command will have different meanings.