Shell special parameters

shell-special-parameters.zsh

# from https://stackoverflow.com/questions/5163144/what-are-the-special-dollar-sign-shell-variables
# Aslo see https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html

$1# (, $2, $3 , ...) are the positional parameters.
"$@" # is an array-like construct of all positional parameters, {$1, $2, $3 ...}.
"$*" # is the IFS expansion of all positional parameters, $1 $2 $3 ....
$# # is the number of positional parameters.
$- # current options set for the shell.
$$ # pid of the current shell (not subshell).
$_ # most recent parameter (or the abs path of the command to start the current shell immediately after startup).
$IFS # is the (input) field separator.
$? # is the most recent foreground pipeline exit status.
$! # is the PID of the most recent background command.
$0 # is the name of the shell or shell script.