If you see this file, it's because you have a cvs snapshot of flex. If you are not interested in flex development or you are not in need of the latest bleeding-edge features, then this snapshot is not for you. When you get a distribution of flex, a large number of intermediate files needed to make building flex easy are included. You don't have that in this snapshot. You will need various external tools in order to build the distribution. Here is a (possibly incomplete) list of the required tools. Always get the latest version of each tool: compiler suite; e.g., gcc bash or some other fairly robust sh-style shell GNU bison; to generate parse.c from parse.y GNU m4; required by BNU autoconf (yes, it *must* be GNU m4) GNU autoconf and GNU automake; for generating Makefiles etc. GNU gettext; for i18n flex; for bootstrap of scan.l help2man; to generate man page tar, gzip, etc.; for packaging of the source distribution texinfo tools; to build and test the flex manual perl; GNU automake and GNU autoconf now depend on perl to run ONce you have all the necessary tools installed, life becomes simple. To prepare the flex tree for building, run the script: $ ./autogen.sh in the top level of the flex source tree. This script calls the various tools needed to get flex ready for the GNU-style configure script to be able to work. From this point on, building flex follows the usual configure, make, make install routine.