@ARGV - Contains the command-line arguments for the script (not including the command name [like in C], which is in $0).
[...]
$_ - Alternative: $ARG
The default input, output, and pattern-searching space.
[...]
$! - Alternative: $OS_ERROR, $ERRNO
Used in a numeric context, yields the current value of errno.  Used in a string context, yields the corresponding error string.