Psignal produces a short message on the standard error file describing the indicated signal. First the argu-
ment string s is printed, then a colon, then the name of the signal and a new-line. Most usefully, the argu-
ment string is the name of the program which incurred the signal. The signal number should be from among
those found in <signal.h>.
To simplify variant formatting of signal names, the vector of message strings sys_siglist is provided; the
signal number can be used as an index in this table to get the signal name without the newline. The define
NSIG defined in <signal.h> is the number of messages provided for in the table; it should be checked because
new signals may be added to the system before they are added to the table.