SIGNAL(3F)          UNIX Programmer's Manual           SIGNAL(3F)

NAME
     signal - change the action for a signal

SYNOPSIS
     integer function signal(signum, proc, flag)
     integer signum, flag
     external proc

DESCRIPTION
     When a process incurs a signal (see _s_i_g_n_a_l(2)) the default
     action is usually to clean up and abort.  The user may
     choose to write an alternative signal handling routine.  A
     call to _s_i_g_n_a_l is the way this alternate action is specified
     to the system.

     _S_i_g_n_u_m is the signal number (see _s_i_g_n_a_l(2)).  If _f_l_a_g is
     negative, then _p_r_o_c must be the name of the user signal han-
     dling routine.  If _f_l_a_g is zero or positive, then _p_r_o_c is
     ignored and the value of _f_l_a_g is passed to the system as the
     signal action definition.  In particular, this is how previ-
     ously saved signal actions can be restored.  Two possible
     values for _f_l_a_g have specific meanings: 0 means "use the
     default action" (See NOTES below), 1 means "ignore this sig-
     nal".

     A positive returned value is the previous action definition.
     A value greater than 1 is the address of a routine that was
     to have been called on occurrence of the given signal.  The
     returned value can be used in subsequent calls to _s_i_g_n_a_l in
     order to restore a previous action definition.  A negative
     returned value is the negation of a system error code.  (See
     _p_e_r_r_o_r(3F))

FILES
     /usr/lib/libU77.a

SEE ALSO
     signal(2), kill(3F), kill(1)

NOTES
     f77 arranges to trap certain signals when a process is
     started.  The only way to restore the default f77 action is
     to save the returned value from the first call to _s_i_g_n_a_l.

     When a user signal handling routine is called, UNIX resets
     the signal action definition to its original default value.
     Thus it is necessary to call _s_i_g_n_a_l(3F) from within the user
     signal handler in order to catch subsequent occurrences of
     the same signal. See _s_i_g_n_a_l(2) for a fuller explanation.

     If the user signal handler is called, it will be passed the
     signal number as an integer argument.

Printed 7/31/83                                                 1