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

The name of the label terminates with the first literal newline, not at the semi-colon. There are two easy ways to solve the problem. Add literal newlines:

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

Or use multiple -e options:

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

Answer 2

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: /'