script problem

Shell Programming and Scripting
1

Hi All

In a script (ksh), I want a user to enter 4 characters, these can be a mix of letters (uppercase and lowercase) and numbers.

In this example $var represents what the user has entered.

eg $var can be A9xZ, 3DDL, bbHp .........etc

I need to check that the user has only entered characters so I added the following code:

# Check for invalid characters
echo "$var" | grep [^a-zA-Z0-9] >/dev/null
if [ $? -eq 0 ]
then
echo "$var is not valid."
fi

This appears to work ok unless the user enters a wildcard character.

For example if the user enters bin*, the script expands the * and makes $var equal to all files in the current directory which start with bin.

So $var is "bin bindir binary"

My question is how can I process $var literally as "bin*" in the above grep statement?

Thanks for your help
Helen
:confused:

2

try grep [^a-zA-Z0-9 add your list of metacharictures here]

3

Hello Helen,

echo "$var" | grep [^a-zA-Z0-9] >/dev/null
will return a 0 if $var is "bin*" because the grep is only serching for alphabetic characters and numbers.

Plus if you do: echo "$var"
This will return: bin*

However, if you do(without quotes): echo $var
This will return: bin binary ....

If you do want * to be a valid character you can put a (backslash) \ before it in the grep statement. This turns off any special meanings of such characters.

Hope this answers your question.
Regards

4

You should forget about grep anyway. ksh can do this all by itself without invoking an external program. Try:

if [[ $var = +([a-zA-Z0-9]) ]] ; then
        echo $var is ok
else
        echo $var is an error
fi

Note that you must use the double bracket not the single bracket.

5

Thanks for all your help on this :wink: