postgresql build error

Hi,
I'm trying to build postgresql from cvs repository.
I installed flex on my system. it is giving the error that flex is not
available on the system for creating bootscanner.c file. Below is the
complete output
of gmake
gmake -C doc all
gmake[1]: Entering directory `/export/home/schava/pgsql/doc'
gmake[1]: Nothing to be done for `all'.
gmake[1]: Leaving directory `/export/home/schava/pgsql/doc'
gmake -C src all
gmake[1]: Entering directory `/export/home/schava/pgsql/src'
gmake -C backend all
gmake[2]: Entering directory `/export/home/schava/pgsql/src/backend'
gmake -C access all
gmake[3]: Entering directory
`/export/home/schava/pgsql/src/backend/access'
gmake -C common SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/common'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/common'
gmake -C gist SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/gist'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/gist'
gmake -C hash SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/hash'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/hash'
gmake -C heap SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/heap'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/heap'
gmake -C index SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/index'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/index'
gmake -C nbtree SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/nbtree'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/nbtree'
gmake -C rtree SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/rtree'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/rtree'
gmake -C transam SUBSYS.o
gmake[4]: Entering directory
`/export/home/schava/pgsql/src/backend/access/transam'
gmake[4]: `SUBSYS.o' is up to date.
gmake[4]: Leaving directory
`/export/home/schava/pgsql/src/backend/access/transam'
gmake[3]: Leaving directory
`/export/home/schava/pgsql/src/backend/access'
gmake -C bootstrap all
gmake[3]: Entering directory
`/export/home/schava/pgsql/src/backend/bootstrap'
***
ERROR: `flex' is missing on your system. It is needed to create the
file `bootscanner.c'. You can either get flex from a GNU mirror site
or download an official distribution of PostgreSQL, which contains
pre-packaged flex output.
***
gmake[3]: *** [bootscanner.c] Error 1
gmake[3]: Leaving directory
`/export/home/schava/pgsql/src/backend/bootstrap'
gmake[2]: *** [bootstrap-recursive] Error 2
gmake[2]: Leaving directory `/export/home/schava/pgsql/src/backend'
gmake[1]: *** [all] Error 2
gmake[1]: Leaving directory `/export/home/schava/pgsql/src'
gmake: *** [all] Error 2

Thanks and any help is appreciated.
chava