check these

Code:

if [[ $answer != [a-zA-Z]*[a-zA-Z0-9_-] ]]; then echo ok; fi
ok

from the bash manual it says for [[ expression ]]

Code:

Any part of the pattern may be quoted to force it to be matched as a string.

and you can try like this [but wild char(asteriks) doesnot cause the expansion]

Code:

# if [ "$answer" != "[a-zA-Z]*[a-zA-Z0-9_-]" ]; then echo ok; fi
ok

i remove the parentheses because it does not like seem as special chars.

and this may be like this

Code:

......
elif [[ $answer != [a-zA-Z]*[a-zA-Z0-9_-] ]]
then
echo "answer value is not equal to the pattern"
else
echo "answer is equal to the pattern "
fi

if used the asteriks(*) char in the your regex then you must be it in the quotes for escaping its meaning so shell is not to expand it.

Code:

# echo *  --> all files
# echo "*" --> asteriks char

Code:

*	The preceding item will be matched zero or more times.

so it is ok because asteriks char matches S* -> [ SK_BTS04A_hiQ_01b ]

Code:

# if [[ $answer == [a-zA-Z]*[a-zA-Z0-9_-] ]] ; then echo ok ;fi
ok

with single square brackets bash gives error beacuse of [a-z] and other expression's expansion brings a lot of char sets and does not recognized by shell by globbing '*' and single bracket have not capable of manage this.

Code:

# if [ $answer == [a-zA-Z]*[a-zA-Z0-9_-] ] ; then echo ok ;fi
-bash: [: too many arguments

with double brackets bash manages it with quotes (you can think word splitting automatically created with the double quotes in the [[..]] to IFS)

Code:

# if [[ $answer == [a-zA-Z]*[a-zA-Z0-9_-] ]] ; then echo ok ;fi
ok

regards
ygemici