sysafe, "command line"
or system, "command line"
pass the command line to a UNIX sh (Bourne) shell for execution.
This requires a fork() system call, which in turn makes a copy of
the yorick executable in virtual memory before replacing that copy
with the sh shell. If yorick has grown to enormous size, the copy
can bring your machine to its knees or kill it. If you include
sysafe.i before yorick grows (before you start the calculation that
requires the large data arrays), a pipe is opened to an sh which
remains running, and the original system command is replaced by
sysafe. Future system commands will be piped to the already
running sh, so no dangerous copy operation is required.
There are four problems with this approach:
(1) You can't run interactive programs with sysafe, because the
stdin is from the pipe (sysafe_pipe) instead of the keyboard.
Attempting to do so may lock up yorick.
(2) Since the command runs asynchronously now, yorick can't wait
until it completes, and yorick's prompt will often precede
the output from the command, unlike using the default system
(3) Some typographical errors in commands may kill the sh; since
you don't start a new one each time, the system command will
(4) The shorthand $ syntax still uses the dangerous system call;
you need to call system as an ordinary function for sysafe
to protect you.
interpreted function, defined at i/sysafe.i line 10