sed “undefined label” on MacOS

Question

I recently found out that this simple sed expression work fine on Linux or under Cygwin but fails on Mac with an \"undefined label\" error:

$ sed \'         


        

Answer 1

There are a bunch of similar questions on SO but most of them are due to the behavior of -i differing between platforms, so this is different.

In this case, the issue is rather simple: it seems like label references can only go backwards in the BSD version of sed, whereas the GNU version allows to use forward references. That is on MacOS, the :label must appear before the b label.

The solution is to rewrite the expression to either define the label before the branch, or in the case of the expression above realize the branch is a kind of "if this pattern is not present ... jump ahead". In this case the expression can be expanded to not need the label in the first place:

sed '/SUCCESSFUL/d ; /\s+\[java\]\s*/d; /\[java\]/s/\s\+\[java\]//; /Compiling/!d; /^\s*$$/d; s/^/monitor: /'