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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 section 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 section 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 `stdio.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.
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