• GNU Libtool
• m4
• autoconf
• gettext
• automake
• Bison（任意）
• GNU help2man（任意）
• Texinfo（任意）
• GNU Indent（任意）

$ wget https://github.com/westes/flex/releases/download/v2.6.4/flex-2.6.4.tar.gz
$ tar xvf flex-2.6.4.tar.gz
$ cd flex-2.6.4/
$ LIBTOOLIZE=/opt/libtool/2.4.6/bin/libtoolize \
  PATH=/opt/automake/1.16.3/bin:/opt/gettext/0.21/bin:/opt/autoconf/2.69/bin:/opt/m4/1.4.18/bin:${PATH} \
  ./autogen.sh 
$ ./configure \
  PATH=/opt/indent/2.2.12/bin:/opt/texinfo/6.7/bin:/opt/help2man/1.47.16/bin:/opt/bison/3.7.4/bin:/opt/m4/1.4.18/bin:${PATH} \
  --prefix=/opt/flex/2.6.4 \
  CFLAGS='-g -O2 -D_GNU_SOURCE'
$ make
$ make install

$ export PATH=/opt/flex/2.6.4/bin:${PATH}
$ export LD_LIBRARY_PATH=/opt/flex/2.6.4/lib:${LD_LIBRARY_PATH}
$ export C_INCLUDE_PATH=/opt/flex/2.6.4/include:${C_INCLUDE_PATH}
$ export CPLUS_INCLUDE_PATH=/opt/flex/2.6.4/include:${CPLUS_INCLUDE_PATH}