The [$] symbol in linux is the "command prompt", which means you can enter the command [1] at the end. The command prompt may prompt some information about the current user. In linux The user will be prompted for the current directory and current user.
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$0 The execution name of this program
$n The nth parameter of this program Value, n=1..9
#$* All parameters of this program, this option parameter can exceed 9.
$# The number of parameters of this program
$$ The PID of this program (the current process ID number of the script running)
$! The PID of the last background command executed (the process ID number of the last process running in the background)
$? The return of the previous command Value (displays the exit status of the last command. 0 indicates no error, any other value indicates an error)
$-Displays the current options used by the shell, the same function as the set command
$@ Similar to $*, but can be used as an array
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