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MySQL Cookbook
book

MySQL Cookbook

by Paul DuBois
October 2002
Intermediate to advanced content levelIntermediate to advanced
1024 pages
27h 26m
English
O'Reilly Media, Inc.
Content preview from 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 ...

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Publisher Resources

ISBN: 0596001452Catalog PageErrata