Some special variables in shell scripts

In shell scripts, there are some common special variable representations that need to be known.

Here are some of the frequently used special variable representations:

$ Current PIN name
$ ... Parameters of the incoming script or function (greater than 10 are enclosed in curly braces)
$# the number of arguments to the incoming script or function
$* Printing all incoming parameters
[Email protected] Print all incoming parameters
When an incoming parameter has double quotation marks,
$* is the overall output, [email protected] is the output of each parameter
$? Last command or function exit status
$$ Current shell script process ID
$-shows the current options used by the shell (flag passed to the script), which is the same function as the SET command
$! The last working PID that runs in the background
$_ last parameter of the command executed before saving
$UID Print the Uid,root UID for the current user is 0

Some special variables in shell scripts