MySQL Cookbook

Using Patterns to Match Numeric Values

Problem

You need to make sure a string looks like a number.

Solution

Use a pattern that matches the type of number you’re looking for.

Discussion

Patterns can be used to classify values into several types of numbers:

Pattern	Type of value the pattern matches
/^\d+$/	Unsigned integer
/^-?\d+$/	Negative or unsigned integer
/^[-+]?\d+$/	Signed or unsigned integer
/^[-+]?(\d+(\.\d*)?|\.\d+)$/	Floating-point number

The pattern /^\d+$/ matches unsigned integers by requiring a nonempty value that consists only of digits from the beginning to the end of the value. If you care only that a value begins with an integer, you can match an initial numeric part and extract it. To do this, match just the initial part of the string (omit the $ that requires the pattern to match to the end of the string) and place parentheses around the \d+ part. Then refer to the matched number as $1 after a successful match:

if ($val =~ /^(\d+)/)
{
    $val = $1;  # reset value to matched subpart
}

You could also add zero to the value, which causes Perl to perform an implicit string-to-number conversion that discards the non-numeric suffix:

if ($val =~ /^\d+/)
{
    $val += 0;
}

However, if you run Perl with the -w option (which I recommend), this form of conversion generates warnings for values that actually have a non-numeric part. It will also convert string values like 0013 to the number 13, which may be unacceptable in some contexts.

Some kinds of numeric values have a ...