$# Number of arguments
$* All positional arguments (as a single word)$@ All positional arguments (as separate strings)$1 First argument
$_ Last argument of the previous command
Note: $@ and $* must be quoted in order to perform as described. Otherwise, they do exactly the same thing (arguments as separate strings).
特殊变量
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Special variables
$? Exit status of last task
$! PID of last background task
$$ PID of shell
$0 Filename of the shell script
$_ Last argument of the previous command
