WORD=abcd1234
echo $WORD | grep -oE [[:digit:]] | wc -l
4

COUNT=`echo $WORD | grep -oE [[:digit:]] | wc -l`

if [ `echo $WORD | cut -c 4-8  | grep -oE [[:digit:]] | wc -l` -eq 5 ]
then
do this...

$ cat ./testgrep.ksh
#!/bin/ksh

WORD=abc12345

echo $WORD|grep -qE "[[:digit:]]{5}$"
if [ $? -eq 0 ]; then
     echo "Do this with $WORD"
else
     echo "Else do this with $WORD"
fi

WORD2=ab123456

echo $WORD2|grep -qE "[[:digit:]]{5}$"
if [ $? -eq 0 ]; then
     echo "Do this with $WORD2"
else
     echo "Else do this with $WORD2"
fi

WORD3=abc1234

echo $WORD3|grep -qE "[[:digit:]]{5}$"
if [ $? -eq 0 ]; then
     echo "Do this with $WORD3"
else
     echo "Else do this with $WORD3"
fi

exit 0

$ ./testgrep.ksh
Do this with abc12345
Do this with ab123456
Else do this with abc1234

$ WORD=abcd1234
$ [[ $WORD  =~ [0-9]{5}$ ]] && echo OK || echo KO
KO
$ WORD=abcd12345
$ [[ $WORD  =~ [0-9]{5}$ ]] && echo OK || echo KO
OK

#!/bin/ksh

WORD=abcd1234

[[ $(echo "${WORD}" | awk '{print gsub("[0-9]", "")}')  -eq 5 ]] && echo OK || echo KO

% perl -le'print shift=~/\d{5}$/?"OK":"KO"' abcd1234
KO
% perl -le'print shift=~/\d{5}$/?"OK":"KO"' abcd12345
OK