SYSTEM(s)

This function takes the string s, passes it to a bourne shell, and
returns as a result all text produced by that shell command on the
standard output. This function has a side effect, namely that the
variable `rc' is set to the exit status of the shell, or -1 if the shell
couldn't be invoked for some reason.  This may in turn cause the
condition "ERROR" or "FAILURE" to be trapped (see the SIGNAL ON and
CALL ON instructions).  Except in the case that a "SIGNAL" occurs,
there will always be a result whatever the return code, but it may be
the null string if an error occurred (or if the command produced no
output).