UNIX for Dummies Questions & Answers

       The  following  special  parameters are implicitly set by the shell and
       cannot be set directly using assignments:

       !      Process id of the last background process started.  If no  back-
              ground processes have been started, the parameter is not set.

       #      The number of positional parameters (i.e., $1, $2, etc.).

       $      The process ID of the shell, or the PID of the original shell if
              it is a subshell.

       -      The concatenation of the current single letter options (see  set
              command below for list of options).

       ?      The  exit  status of the last non-asynchronous command executed.
              If the last command was killed by a signal, $?  is  set  to  128
              plus the signal number.

       0      The name the shell was invoked with (i.e., argv[0]), or the com-
              mand-name if it was invoked with the -c option and the  command-
              name was supplied, or the file argument, if it was supplied.  If
              the posix option is not set, $0 is the name of the current func-
              tion or script.

       1 ... 9
              The  first  nine positional parameters that were supplied to the
              shell, function or .-script.  Further positional parameters  may
              be accessed using ${number}.

       *      All  positional  parameters  (except  parameter  0), i.e., $1 $2
              $3....  If used outside of double quotes, parameters  are  sepa-
              rate  words  (which  are  subjected  to word splitting); if used
              within double quotes, parameters  are  separated  by  the  first
              character  of  the  IFS parameter (or the empty string if IFS is
              null).

       @      Same as $*, unless it is used inside  double  quotes,  in  which
              case  a separate word is generated for each positional parameter
              - if there are no positional parameters, no  word  is  generated
              ("$@" can be used to access arguments, verbatim, without loosing
              null arguments or splitting arguments with spaces).

   Positional Parameters
       A  positional  parameter  is a parameter denoted by one or more digits,
       other than the single digit 0.  Positional parameters are assigned from
       the  shell?s  arguments when it is invoked, and may be reassigned using
       the set builtin command.  Positional parameters may not be assigned  to
       with  assignment statements.  The positional parameters are temporarily
       replaced when a shell function is executed (see FUNCTIONS below).

$ cat ./foo.ksh
#!/bin/ksh

echo "$1 $2"
set -- "something" "something_else"
echo "$1 $2"

exit 0
$./foo.ksh foo bar
foo bar
something something_else
$