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 = $1; # reset value to matched subpart }
You could also add zero to the value, which causes Perl to perform an implicit string-to-number conversion that discards the nonnumeric suffix:
if ($val =~ /^\d+/) { $val += 0; }
However, if you run Perl with the
-w
option or include a use
warnings
line in your script (which I
recommend), this form of conversion generates warnings for values that
actually have a nonnumeric part. It will also convert string values
like 0013
to the number 13
, which may be unacceptable in some
contexts.
Some kinds ...
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