how to turn off "buffered output" in R mac os?

hi everyone,
I am writing R with textmate2.0 on my mac book. Today when I want to add a progress bar in a loop, i find the textmate bundle fails to  "print" or "cat" anything until the loop is completed. 
I search for this problem in Google and some says that this is because the "buffers output" setting of R and can be solved by unchoosing Rconsole->Misc->buffered output. However, doesn't anyone notice that the Mac OS R even doesn't have this "buffered output" option?
I have tried the flush.console() but it doesn't work, neither.
Anyone has get into such a problem and can give me a help?