Matt Komarnicki

In my particular case the "illegal offset" issue occured when I wanted to patch a Windows executable in macOS Sequoria.

This is the command I have used:

~/DOSGAMES/LOLG/ sed -b -i -e "s/24\(M,Swap\)/32\1/" LOLG.EXE

Unfortunately this was unsuccessful and returned with:

sed: illegal option -- b
usage: sed script [-EHalnru] [-i extension] [file ...]
	sed [-EHalnu] [-i extension] [-e script] ... [-f script_file] ... [file ...]

Solution

Let's use GNU version of the sed command. The easiest approach is to pull it via Homebrew package manager, follow this link if Homebrew is not present on your macOS. Pull it by typing:

brew install gnu-sed

Once installed, you can validate it by calling which gsed.

Finally swap sed with gsed and carry on with your original command:

gsed -b -i -e "s/24\(M,Swap\)/32\1/" LOLG.EXE

This should do the trick and your file should be modified accordingly to the given arguments. By the way - always remember to backup your target file:

cp LOLG.EXE LOLG.EXE_ORIG

This is it.