Because make cannot find
UNIX_COMMAND_PATH is pointing to
egrep are located in
make cannot find the version of file
UNIX_COMMAND_PATH can be defined as
UNIXCOMMAND_PATH :=$(call PrefixPath,$(ALT_UNIXCOMMAND_PATH))
ln -s /bin/sh /usr/bin/sh
make returns no error. If make complains something not found in /usr/bin/ but it is located in /bin, just make a symbolic link to /bin.