GNU C Library (libc) Programming Guide

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24.2.8 Signal Messages

We mentioned above that the shell prints a message describing the signal that terminated a child process. The clean way to print a message describing a signal is to use the functions strsignal and psignal. These functions use a signal number to specify which kind of signal to describe. The signal number may come from the termination status of a child process (see Process Completion) or it may come from a signal handler in the same process.

— Function: char * strsignal (int signum)

This function returns a pointer to a statically-allocated string containing a message describing the signal signum. You should not modify the contents of this string; and, since it can be rewritten on subsequent calls, you should save a copy of it if you need to reference it later.
This function is a GNU extension, declared in the header file string.h.

— Function: void psignal (int signum, const char *message)

This function prints a message describing the signal signum to the standard error output stream stderr; see Standard Streams.
If you call psignal with a message that is either a null pointer or an empty string, psignal just prints the message corresponding to signum, adding a trailing newline.
If you supply a non-null message argument, then psignal prefixes its output with this string. It adds a colon and a space character to separate the message from the string corresponding to signum.
This function is a BSD feature, declared in the header file signal.h.

There is also an array sys_siglist which contains the messages for the various signal codes. This array exists on BSD systems, unlike strsignal.