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1.1 ! root 1: .TH SIGNAL 3F "18 July 1983" ! 2: .UC 4 ! 3: .SH NAME ! 4: signal \- change the action for a signal ! 5: .SH SYNOPSIS ! 6: .B integer function signal(signum, proc, flag) ! 7: .br ! 8: .B integer signum, flag ! 9: .br ! 10: .B external proc ! 11: .SH DESCRIPTION ! 12: When a process incurs a signal (see ! 13: .IR signal (3C)) ! 14: the default action ! 15: is usually to clean up and abort. ! 16: The user may choose to write an alternative signal handling routine. ! 17: A call to ! 18: .I signal ! 19: is the way this alternate action is specified to the system. ! 20: .PP ! 21: .I Signum ! 22: is the signal number (see ! 23: .IR signal (3C)). ! 24: If ! 25: .I flag ! 26: is negative, then ! 27: .I proc ! 28: must be the name of the user signal handling routine. ! 29: If ! 30: .I flag ! 31: is zero or positive, then ! 32: .I proc ! 33: is ignored and the value of ! 34: .I flag ! 35: is passed to the system as the signal action definition. ! 36: In particular, this is how previously saved signal actions can be restored. ! 37: Two possible values for ! 38: .I flag ! 39: have specific meanings: ! 40: 0 means "use the default action" (See NOTES below), ! 41: 1 means "ignore this signal". ! 42: .PP ! 43: A positive returned value is the previous action definition. ! 44: A value greater than 1 is the address of a routine that ! 45: was to have been called on occurrence of the given signal. ! 46: The returned value can be used in subsequent calls to ! 47: .I signal ! 48: in order to restore a previous action definition. ! 49: A negative returned value is the negation of a system error code. ! 50: (See ! 51: .IR perror (3F)) ! 52: .SH FILES ! 53: .ie \nM /usr/ucb/lib/libU77.a ! 54: .el /usr/lib/libU77.a ! 55: .SH "SEE ALSO" ! 56: signal(3C), kill(3F), kill(1) ! 57: .SH NOTES ! 58: .B f77 ! 59: arranges to trap certain signals when a process is started. ! 60: The only way to restore the default ! 61: .B f77 ! 62: action is to save the returned ! 63: value from the first call to ! 64: .I signal. ! 65: .PP ! 66: If the user signal handler is called, it will be passed the signal number ! 67: as an integer argument.
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