Manual Pages  — PSIGNAL

The psignal() function accepts a signal number argument sig and writes it to the standard error. If the argument s is non- NULL and does not point to the null character, s is written to the standard error file descriptor prior to the message string, immediately followed by a colon and a space. If the signal number is not recognized (sigaction(2)), the string "Unknown signal" is produced.

The message strings can be accessed directly through the external array sys_siglist, indexed by recognized signal numbers. The external array sys_signame is used similarly and contains short, upper-case abbreviations for signals which are useful for recognizing signal names in user input. The defined variable NSIG contains a count of the strings in sys_siglist and sys_signame.