Question

I’m new to UNIX, having only started it at work today, but experienced with Java, and have the following code:

#/bin/bash
echo "Please enter a word:"
read word
grep -i $word $1 | cut -d',' -f1,2 | tr "," "-"> output

This works fine, but what I now need to do is to check when word is read, that it contains nothing but letters and if it has numeric characters in print “Invalid input!” message and ask them to enter it again. I assumed regular expressions with an if statement would be the easy way to do this but I cannot get my head around how to use them in UNIX as I am used to the Java application of them. Any help with this would be greatly appreciated, as I couldn’t find help when searching as all the solutions with regular expressions in linux I found only dealt with if it was either all numeric or not.

Answer 1

Yet another approach. Grep exits with 0 if a match is found, so you can test the exit code:

echo "${word}" | grep -q '[0-9]'
if [ $? = 0 ]; then
    echo 'Invalid input'
fi

This is /bin/sh compatible.

---

Incorporating Daenyth and John’s suggestions, this becomes

if echo "${word}" | grep '[0-9]' >/dev/null; then
    echo 'Invalid input'
fi