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INSTALLING Flex

Should you be here at all?

If building, developing or compiling C programs is new to you, you probably want to use your operating system's standard means of installing software to install flex. If you do not need the latest features of flex, you probably just want to use your operating system's standard means of installing software to obtain flex.

Now that you know you should be here ...

If you are not familiar with bootstrapping C code from a git repository or if GNU autotools seems like a jumble of tenuous incantationery to you, then make sure that you downloaded one of the release tar archives of flex. You can verify this by checking the filename of what you downloaded. If it is something like flex-<version>.tar.<compressiontype> then you have a release tar archive. If you have a filename like flex.tar.gz or flex.zip, you have a copy of the git repository and you didn't download the thing you wanted to.

Building from a release archive

To build flex from a release archive:

$ ./configure <any configure options you need>
$ make

To see what options are available from the configure script:

$ ./configure --help

Optionally run the test suite:

$ make check

To install the flex you just built:

$ make install

Note that you may want to make use of the DESTDIR argument on the make install command line or that you may want to have used the --prefix argument with configure (or mostly equivalently the prefix argument on the make command line).

Building from the git repository

To build from the git repository:

First, make sure you have a copy of flex installed somewhere on your path so that configure can find it. You can usually do this with your operating system's standard means of installing software. Sometimes, you have to build from a recent release of flex, however. Using a version of flex built from the flex codebase is always acceptable if you have already bootstrapped doing so.

You will also need all the programs that flex needs in order to be built from scratch:

  • compiler suite - flex is built with gcc
  • bash, or a good Bourne-style shell
  • m4 - m4 -P needs to work; GNU m4 and a few others are suitable
  • GNU bison; to generate parse.c from parse.y
  • autoconf; for handling the build system
  • automake; for Makefile generation
  • libtool; often packaged with automake, but not always
  • make; for running the generated Makefiles
  • gettext; for i18n support
  • help2man; to generate the flex man page
  • tar, gzip, lzip, etc.; for packaging of the source distribution
  • GNU texinfo; to build and test the flex manual. Note that if you want to build the dvi/ps/pdf versions of the documentation you will need texi2dvi and related programs, along with a sufficiently powerful implementation of TeX to process them. See your operating system documentation for how to achieve this. The printable versions of the manual are not built unless specifically requested, but the targets are included by automake.
  • GNU indent; for indenting the flex source the way we want it done
  • GNU sed; GNU extensions are used so other sed versions will not work

In cases where the versions of the above tools matter, the file configure.ac will specify the minimum required versions.

Then:

$ ./autogen.sh

After autogen.sh finishes successfully, building flex follows the same steps as building flex from a release archive.

Note that, in addition to make check, make distcheck builds a release archive and builds and tests flex from inside a directory containing only known distributed files.

If you have trouble building flex from git sources on non-Debian systems, (e.g. MacOS) make sure that any required GNU tools have been added to your PATH before your system defaults. Also check that required GNU tools are aliased to their typical names - some package systems prefix them with "gnu-" which make them hard for configure to find.