Shift operations in the shell

Positional parameters can be shift shifted left with the command. For example, the shift 3 original $4 now become $1 , the original $5 now become and $2 so on, the original $1 , $2 $3 Discard, $0 do not move. Commands with no parameters are shift equivalent shift 1 .

A very useful Unix command: Shift. We know that for positional variables or command-line arguments, the number must be deterministic, or when the Shell program does not know its number, you can assign all parameters together to the variable $*. If the user requires that the Shell do not know the number of positional variables, but also one by one to the parameter one by one processing, that is, after $ $, after the $ $ $, and so on. The value of the variable before the shift command executes is not available after the shift command executes.

The shift command has another important purpose, and BSH defines 9 positional variables, from $9 to $9, which does not mean that the user can only use the command line with more than 9 parameters, and with the shift command, it is possible to access more than one or more of them.

The shift command moves the number of arguments at a time, specified by the parameters they take. For example, when the shell program finishes processing the first nine command-line arguments, you can use the Shift 9 command to move the $ $ $.

Shift operations in the shell