error while configuring heimdal

["novice heimdal" <heimdal@rediffmail.com>]

i get this errow when i try to run ./configure  --enable-ldapi

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checking for flex... ${SHELL} /root/heimdal-source/heimdal-0.4b/missing --run fl
ex
checking for yywrap in -lfl... no
checking for yywrap in -ll... no
checking lex output file root... /root/heimdal-source/heimdal-0.4b/configure: ${
SHELL}: command not found
configure: error: cannot find output from ${SHELL} /root/heimdal-source/heimdal-
0.4b/missing --run flex; giving up
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any clues??
thanx in advance
vamsi