why this" ^[0-9-]|[0-9-] {1}[0-9\/]*$ " regex is matching for a alphabet character string?

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in fact its matching even blank i m stuck why its not working please help.
it should match a numeric or fraction and only one space charcter and also minus - character.

[EDIT] Sample strings from comment
It should match:

2
2/3
2 2/3 (with one space only)

This is the regex:

^[0-9-]*|[0-9-]* {1}[0-9\/]*$

Posted 21-Dec-14 21:38pm

varun150

Updated 21-Dec-14 22:17pm

George Jonsson

v4

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George Jonsson 22-Dec-14 3:41am

Can you present some example strings you try to match?

varun150 22-Dec-14 3:48am

it should match 2 or 2/3 or 2 2/3 with one space only.

George Jonsson 22-Dec-14 4:19am

That was not easy to figure out from your description.
I added that info to your question.

Kornfeld Eliyahu Peter 22-Dec-14 3:42am

This may help you to understand what you have...
http://www.regexper.com/#%5E%5B0-9-%5D*%7C%5B0-9-%5D*%20%7B1%7D%5B0-9%5C%2F%5D*%24

varun150 22-Dec-14 3:49am

im new to regex i still do not understand diagram at regexper.com

Kornfeld Eliyahu Peter 22-Dec-14 3:53am

Very unfortunate - that diagram is written/drawn in very basic way - no need of doctorate of any kind to follow it...

varun150 22-Dec-14 4:06am

can you please tell me how this diagram can help me correct my regex.
please explain to this newbie your help is much appriciated.

varun150 22-Dec-14 3:45am

it should match 2 or 2/3 or 2 2/3 with one space only.

2 solutions

Solution 2

Even (almost) all is said about the topic, I still have a comment and a possible solution:

your expression fails since you use * instead of + as multiplier
your expression also fails since you use anchors (^...$) but between the anchors, you have an alternative (a|b) - so, the first anchor belongs to the first alternative, the second to the second alternative. I.e. you say: the text may start with zero or more digits or minus signs (i.e. since using the * multiplier, allow to leave that part away, so allowing for any string after that), or it must end on some mixture of digits and spaces (minimal: it ends on one space)
a possible solution for "optional sign followed by integral number with optional quotient, or quotient only": ^[-+]?\d+(?:(?:\s\d+)?\/\d+)?$ (see www.regexper.com[^])

Cheers
Andi

Posted 21-Dec-14 23:08pm

Andreas Gieriet

Comments

Kornfeld Eliyahu Peter 22-Dec-14 5:18am

The only problems is the use of \d it will allow 0 and 0/0 too...

Andreas Gieriet 22-Dec-14 8:00am

That's where you reach the limit of regex, I'd say.
Regex is useful for checking the form, not the content (i.e. the correct value range, etc.).

The OP did not ask for any numeric constraints - he was confused that the regex did not match - reason: missing parenthesis since anchors bind more than the alternative operator, and the * multiplicator operand also matches zero items.

E.g. the following are formally correct but probably not desired values that must be checked with other means:

-0
0/0
1/0
0/1
0 1/2
1/123456789012345678901234567890
123/1
2/2
etc.

Cheers
Andi

PS: In your regex solution with the attempt to also check for proper value ranges, you fail to cover e.g. 0. Trying to check for proper value ranges renders regex patterns to become extremely complex.

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Kornfeld Eliyahu Peter · Accepted Answer · 2014-12-21T22:08:00

Solution 1

According to your comment the regex you are looking for is this:
http://www.regexper.com/#%5E(%5B1-9%5D%5B0-9%5D*)((%5Cs((%5B1-9%5D%5B0-9%5D*)%5C%2F(%5B1-9%5D%5B0-9%5D*)))*%7C(%5C%2F(%5B1-9%5D%5B0-9%5D*))*)%24[^]

^([1-9][0-9]*)((\s(([1-9][0-9]*)\/([1-9][0-9]*)))*|(\/([1-9][0-9]*))*)$

Now let break it apart...

^([1-9][0-9]*)$

This declare a group of numbers where the first digit must be between 1 and 9 and the second can be from 0 to 9 - optionally...

^(\s(([1-9][0-9]*)\/([1-9][0-9]*)))*

This part allows (means this is optional) a single whitespace (\s) and two numbers (like the first one) separated by /...

^(\/([1-9][0-9]*))*$

The last part allows (again it is optional) a / and a number, same like at the beginning...
This will allow 2 and 2/3 and 2 2/3 also

Posted 21-Dec-14 22:08pm

Kornfeld Eliyahu Peter

Comments

Thomas Daniels 22-Dec-14 4:14am

+5!

Kornfeld Eliyahu Peter 22-Dec-14 4:15am

Thank you...

varun150 22-Dec-14 4:18am

thank you so much for help.
i think [0-9] was culprit that matched the null value.

varun150 22-Dec-14 4:20am

what if this fraction or non fraction have - or + sign like +3 or -3/5 or -1 3/5

Kornfeld Eliyahu Peter 22-Dec-14 4:23am

I think that at this point it's your turn :-)

Maciej Los 22-Dec-14 4:23am

+5!

Kornfeld Eliyahu Peter 22-Dec-14 4:23am

Thank you...

varun150 22-Dec-14 4:23am

iadded this at begining[-+] it shuold be acuurate its workin though.

varun150 22-Dec-14 4:23am

^([-+][1-9][0-9]*)((\s(([1-9][0-9]*)\/([1-9][0-9]*)))*|(\/([1-9][0-9]*))*)$

why this" ^[0-9-]*|[0-9-]* {1}[0-9\/]*$ " regex is matching for a alphabet character string?

2 solutions

Solution 2

Solution 1

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why this" ^[0-9-]|[0-9-] {1}[0-9\/]*$ " regex is matching for a alphabet character string?