Some special parameters are automatically set by the Korn shell, and usually cannot be directly set or modified.
$# | number of positional parameters |
$@ | all positional parameters ("$1", "$2", ..., "$n") |
$* | all positional parameters ("$1 $2... $n") |
$? | exit status of the last command |
$$ | process id of the current shell |
$– | current options in effect |
$! | process id of last background command |
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