RegEx that matches positive numbers

I need to write a regex to allow only positive number ( integers or decimals). I have found this:

/^(?!(?:0|0.0|0.00)$)[+]?d+(.d|.d[0-9])?$/


but it just accepts up to 2 decimal places. What changes do I have to make, so that it can accept any number of decimal places?

Also where can I find a good tutorial for learning regex.

Thanks beforehand

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4 Answers
4

This would be my way: ^[+]?d+([.]d+)?$
EDIT: If you want to allow something like .23, you could use ^[+]?([.]d+|d+([.]d+)?)$
EDIT: tchrist insists on this one: allowing 4., you could use ^[+]?([.]d+|d+[.]?d*)$

^[+]?d+([.]d+)?$

.23

^[+]?([.]d+|d+([.]d+)?)$

4.

^[+]?([.]d+|d+[.]?d*)$

Explanation:

Note: This will not accept a negative number, which is what you ultimately want.

.23

d+

".23"

The short answer is that you need this pattern:

^(?!(?:^[-+]?[0.]+(?:[Ee]|$)))(?!(?:^-))(?:(?:[+-]?)(?=[0123456789.])(?:(?:(?:[0123456789]+)(?:(?:[.])(?:[0123456789]*))?|(?:(?:[.])(?:[0123456789]+))))(?:(?:[Ee])(?:(?:[+-]?)(?:[0123456789]+))|))$


The long answer is contained in the following program:

#!/usr/bin/perl

use strict;
use warnings qw<FATAL all>;

my $number_rx = qr{

# leading sign, positive or negative
(?: [+-] ? )

# mantissa
(?= [0123456789.] )
(?:
# "N" or "N." or "N.N"
(?:
(?: [0123456789] + )
(?:
(?: [.] )
(?: [0123456789] * )
) ?
|
# ".N", no leading digits
(?:
(?: [.] )
(?: [0123456789] + )
)
)
)

# abscissa
(?:
(?: [Ee] )
(?:
(?: [+-] ? )
(?: [0123456789] + )
)
|
)
}x;

my $negative_rx = qr{ ^ - }x;
my $zero_rx = qr{ ^ [-+]? [0.]+ (?: [Ee] | $ ) }x;

my $positive_rx = qr{
^
(?! $zero_rx )
(?! $negative_rx )
$number_rx
$
}x;

my @test_data = qw{
-2 2 +2 2. -1 1 +1 1.
0 +0 -0 .0 0.
1.3 -3.2 5.13.7
00.00 +00 -00 +0-1
0000.
McGillicuddy
+365.2425
6.02e23
.0000000000000000000000000000000000000000000000000000000000000000000
.00000000000000000000000000000000000000000000000000000000000000000000000001
.03 0.3 3.0
0e50 0e-50
1e50 1e+50 1e-50
};


for my $n (@test_data) {
printf "%s is%s a positive number.n",
$n, $n =~ /$positive_rx/ ? "" : " not";
}


The test results are:

-2 is not a positive number.
2 is a positive number.
+2 is a positive number.
2. is a positive number.
-1 is not a positive number.
1 is a positive number.
+1 is a positive number.
1. is a positive number.
0 is not a positive number.
+0 is not a positive number.
-0 is not a positive number.
.0 is not a positive number.
0. is not a positive number.
1.3 is a positive number.
-3.2 is not a positive number.
5.13.7 is not a positive number.
00.00 is not a positive number.
+00 is not a positive number.
-00 is not a positive number.
+0-1 is not a positive number.
0000. is not a positive number.
McGillicuddy is not a positive number.
+365.2425 is a positive number.
6.02e23 is a positive number.
.0000000000000000000000000000000000000000000000000000000000000000000 is not a positive number.
.00000000000000000000000000000000000000000000000000000000000000000000000001 is a positive number.
.03 is a positive number.
0.3 is a positive number.
3.0 is a positive number.
0e50 is not a positive number.
0e-50 is not a positive number.
1e50 is a positive number.
1e+50 is a positive number.
1e-50 is a positive number.


"OR nothing"

?

(?:foo|)

(?:foo)?

This should do it.

+?(d+(.(d+)?)?|.d+)


There are tons of regular expression tutorials out there, here is one of them:

http://www.cs.tut.fi/~jkorpela/perl/regexp.html

.14159

100.

This one is kinda simple — /d*(.d*)?/g

/d*(.d*)?/g

Update: this one doesn't match empty strings — /(.)?d+(.d*)?/g
Tested on "-1.5 0 12. -123.4. 15 -2. .4"

/(.)?d+(.d*)?/g

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