How do I check if a number entered is between 1 and 31

I am trying to capture the day of the month from the user 开发者_高级运维and want to check if the day is valid - between 1 and 31. I don't want the user to have to add a leading 0 to single digit days. How do I accomplish this check in a bash if statement?

Thanks.

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This is not a job for a regular expression!

This is a job for a conditional expression.

Here's some code to get you started.

if [[ $number -lt 31 ]]; then 
    echo $number is less than 31
else 
    echo $number is greater than 31
fi

Of course, date validation is far more complex than this. How many days are there in February?

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Use the right tool for the job. Regex is not the right tool for this job.

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Just do a numeric comparison:

if (( var >= 1 && var <= 31))
then
    echo "Valid"
fi