01/29/86  on

Syntax as a command:
   on conditions handler_com_line {-control_args} subject_com_line


Syntax as an active function:
   [on conditions handler_com_line {-control_args} subject_com_line]


Function: establishes a handler for a specified set of conditions,
executes an embedded command line with this handler in effect, and then
reverts the handler.  The handler is another embedded command line to
be executed if the condition is signaled.


Arguments:
conditions
   is a list of condition names separated by commas to be trapped by
   the command.
handler_com_line
   is the command line to be executed when one of the conditions
   contained in the list of condition names is raised.  If
   handler_com_line contains spaces or other command language
   characters, enclose it in quotes.  If no command is to be executed
   when a condition is raised, give handler_com_line as "".
subject_com_line
   is the command line to be executed under the control of on; it
   consists of the remaining arguments.  Quote it if it contains
   parentheses, brackets, quotes, or semicolons.


Control arguments:
-brief, -bf
   suppresses the comment printed when a condition occurs.
-cl
   establishes a new command level after the execution of
   handler_com_line.  You cannot use it in the active function.  The
   state of subject_com_line is preserved.  If you issue the start
   command, the same action is taken as would have been had you not
   specified -cl.
-exclude STR, -ex STR
   prevents on from trapping the conditions given in STR.  If you list
   more than one condition, separate condition names by commas.  This
   control argument is useful when handling the any_other condition.


-long, -lg
   prints a detailed message describing the condition raised if one is
   available.  This message is the same as the one printed by the
   reprint_error command.
-restart, -rt
   continues execution of the subject_com_line after execution of
   handler_com_line or, if you also selected -cl, after execution of
   start.  It is incompatible with -retry_command_line.
-retry_command_line, -rcl
   aborts and executes over again subject_com_line after executing
   handler_com_line.


Notes: The default action after executing handler_com_line is to abort
the execution of subject_com_line.

If a condition is raised and trapped by on while executing the
handler_com_line, it is considered a recursive signal and the entire
invocation is aborted.

See the Programmer's Reference Manual for a list of standard system
conditions.


Notes on active function: The active function returns "true" if any of
the specified conditions are signaled during the execution of
subject_com_line, "false" otherwise.


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Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved