The dtruss man page says:
-f follow children as they are forked
which sounds like exactly what I want. However, observe the following behavior:
WhiteAndNerdy% uname -a
Darwin WhiteAndNerdy.local 13.4.0 Darwin Kernel Version 13.4.0: Wed Dec 17 19:05:52 PST 2014; root:xnu-2422.115.10~1/RELEASE_X86_64 x86_64
WhiteAndNerdy% sudo dtruss -f -t writev /bin/echo hello world
hello world
PID/THRD SYSCALL(args) = return
37273/0x90e264: writev(0x1, 0x7F8832D00000, 0x4) = 12 0
WhiteAndNerdy% sudo dtruss -f -t writev sh -c '/bin/echo hello world'
PID/THRD SYSCALL(args) = return
WhiteAndNerdy% sudo dtruss -f -t writev bash -c '/bin/echo hello world'
PID/THRD SYSCALL(args) = return
WhiteAndNerdy% sudo dtruss -f -t writev zsh -c '/bin/echo hello world'
PID/THRD SYSCALL(args) = return
37295/0x90e39b: fork() = 0 0
WhiteAndNerdy% sudo dtruss -f -t writev env /bin/echo hello world
PID/THRD SYSCALL(args) = return
WhiteAndNerdy%
Note that except for the first case, "hello world" is not printed. (And it isn't just a matter of the output not being seen; if I run a process that takes a long time, it doesn't take any time under the sh -c and similar cases. In all the experiments I've done, it appears that execution simply stops at the first exec.)
So, I'm puzzled what dtruss -f actually does. How can I get it to behave like strace -f on Linux, which does what I want?
Motivation: I'm doing some Haskell development on OS X, and would like to trace what's happening during a run of cabal (Haskell's build system). Running dtruss -f on cabal returns without doing anything at all, because in the OS X version of the Haskell Platform, /usr/bin/cabal is a shell script which execs /Library/Haskell/bin/cabal.real. Of course, I can get around that problem by just running /Library/Haskell/bin/cabal.real directly, but that still doesn't buy me much, since cabal.real is just going to turn around and exec a bunch of other stuff. (Think make if you're not familiar with Haskell.)