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How to include dot once as last character in regex?

I'm trying to make regex in JavaScript that matches numbers between 1-100 and includes two decimals.
Example numbers that need to be included in the regex:
1
1.1
1.15
0.5
100
100.00
Example numbers that need to be excluded:
101
100.01
100.1
55.999
This is my regex at the moment:
^(?:100(?:\.00?)?|\d?\d(?:\.\d\d?)?)$
This works otherwise but I also need to include two numbers followed by a decimal or 100 followed by a decimal like this:
14.
9.
100.
This is because I'm running the regex check each time a button is pressed in an input field and even though number like 0.5 is allowed by the current regex, I can't type it in because 0. is not allowed.

You will need to use two separate regexps here, one for the live input validation (just what you described in the question, that will let you input allowed values), and another one for a final "on-submit" validation (that will check the validity of the whole input string).
Otherwise, you won't be able to input 0.5 like values.
The regex for live input validation is:
/^(?:100(?:\.0?0?)?|\d\d?(?:\.\d?\d?)?)$/
See this regex demo. Note how the ? quantifiers make patterns optional, especially the \d and 0 after \. patterns.
The regex for final validation of numbers starting with 0.01 to 100 is
/^(?!0*(?:\.0*)?$)(?:100(?:\.00?)?|\d?\d?(?:\.\d\d?)?)$/
See this regex demo.

Make the numbers after the dot optional, too.
^(?:100(?:\.00?)?|\d?\d(?:\.\d{0,2})?)$
If you want to disallow 0 before the dot if the numbers after are all zero or nothing, probably include a separate negative lookahead for that:
^(?:100(?:\.00?)?|(?!0\.0*$)\d?\d(?:\.\d{0,2})?)$
Nothing here or in your original regex should disallow 0.5; perhaps add more debugging details if that is genuinely something you are grappling with.

You may use this regex for your task:
^(?:0?\.(?:\d?[1-9]|[1-9]\d)|[1-9]\d?(?:\.\d{1,2})?|100(?:\.0{1,2})?)$
RegEx Demo

With your shown samples, could you please try following.
^(?:100(?:\.0{1,2})?|(?:(?:\d\d?)(?:\.\d{1,2})?))$
Online demo for above regex
Explanation: Adding detailed explanation for above.
^ ##Matching from starting of value here.
(?: ##Starting 1st capturing group here.
100(?:\.0{1,2})?| ##matching 100 with or without 1 to 2 zeroes OR
(?: ##Starting 2nd capturing group here.
(?:\d\d?) ##In a non-capturing group matching 0 to 9 and 0 to 9 optional.
(?:\.\d{1,2})? ##In a non-capturing group matching dot followed by 1 or 2 digits
) ##Closing 2nd capturing group here.
)$ ##Closing 1st capturing group at the end of value.

regex to not allow two zeros in the end of a number

I am trying to implement input number field which will not allow if number end with two 0's i.e. if I enter 23100 then it should not allow it.
I'm using the regex /^[0-9]*00$/ but it allowing 123100.
I have pasted my code
enter code here

You may use
/^(?!\d*00$)\d+$/
It will match
^ - start of string
(?!\d*00$) - a negative lookahead that makes sure no 0+ digits followed with 00 at the end are allowed
\d+ - one or more digits
$ - end of string

Updated now to now use look-behinds or look-aheads.
^\d*(?:\d?[1-9]|[1-9]\d)$
Demo

try this.
(^\d+[1-9]+0{0,1}$)
This will work for numbers like
12
123
12310
etc
any number with 2 or more 0's at the end doesn't match in this case

RegEx a name with special characters in javascript

I'm relative new to RegEx and I've encountered a problem. I want to regex a name. I want it to be max 100 characters, contain at least 2 alphabetic characters and it will allow the character '-'.
I have no problem to only check for alphabetic characters or both alphabetic characters and hyphen but I dont't want a name that potantially can be '---------'.
My code without check for hyphens is
var nameRegExp = /^([a-z]){2,100}$/;
An explanation for the code is appreciated as well.
Thanks!

I guess
/^(?=.*[a-z].*[a-z])[a-z-]{1,100}$/
the lookahead part (^(?=.*[a-z].*[a-z])) checks if there are at least two letters. This pattern ("start of string, followed by...") is a common way to express additional conditions in regexes.
You can limit the number of - by adding a negative assertion, as #Mike pointed out:
/^(?=.*[a-z].*[a-z])(?!(?:.*-){11,})[a-z-]{1,100}$/ // max 10 dashes
however it might be easier to write an expression that would match "good" strings instead of trying to forbid "bad" ones. For example, this
/^[a-z]+(-[a-z]+)*$/
looks like a good approximation for a "name". It allows foo and foo-bar-baz, but not the stuff like ---- or foo----bar----.

To limit the number of - you could add a negative look-ahead, where the number 3 is one more than the maximum number you want to allow
/^(?!(?:[a-z]*-){3,})(?=-*[a-z]-*[a-z])[a-z-]{2,100}$/

Regular Expression with optional elements in input string in javascript

Can anyone give me the regular expression for currency which have the following formats :
1000 - valid
1,000 - valid
1,000.00 or 1000.00 - valid.
This means, the number May or May Not contain a comma(,) separator every 3 digits.
The number May Or May Not contain a dot (.), and if it carries a dot(.) it should show atleast 1 number after the decimal place.
And lastly it should be numerical characters only. If I need to make my question clear kindly suggest.

/^\d{1,3}(?:(?:,\d{3})*|(?:\d{3})*)(?:\.\d{1,2})?$/
"Between one and three digits, then any number of groups of three digits prefixed by a comma or any number of groups of three digits not prefixed by said comma (disallowing a mix of the two kinds of groups), then an optional group of one or two digits prefixed by a dot."
Note: This regex assumes that you want to validate an entire string against the criteria outlined in your question. If you want to use it to find such numbers in a longer string, you will need to remove the ^ and $ from the beginning and end of the expression.

Something like so should work: (,?\d{3})+(\.\d{2})?. The regex will attempt to match a sequence of 3 digits precedeed by an optional comma, which is then, finally followed by an optional decimal point and 2 digits.
Please refer to this tutorial for more information.
EDIT: As per the comment below, the above regex can fail. I would recommend first using this regular expression: ^[\d][\d.,]+$ to make sure that you only have digits, thousand and decimal seperators. This regular expression will also make sure that the number starts with a digit, not with anything else. You could most likely have one regular expression which does everything, but it will most likely be quite complex.

Regex to validate brazilian money using Javascript

I need to validate some form fileds that contain brazilian money (its name is "Real") using Javascript. It has the following format:
0,01
0,12
1,23
12,34
123,45
1.234,56
12.235,67
123.456,78
1.234.567,89
12.345.678,90
123.456.789,01
1.234.567.890,12
My regex knowledge is weak, can somebody help me please?

Does this do what you want?
^\d{1,3}(?:\.\d{3})*,\d{2}$
That says "1 to 3 digits, optionally followed by any number of groups of three digits preceded by a period, followed by a comma and two more digits." If you want to allow the leading whitespace present in your example, add \s* to the front:
^\s*\d{1,3}(?:\.\d{3})*,\d{2}$
EDIT: As #ElRonnoco pointed out, the above regular expression accepts leading zeroes (e.g. 010.100,00). To disallow those, you may use this longer version:
^\s*(?:[1-9]\d{0,2}(?:\.\d{3})*|0),\d{2}$
EDIT 2 The above regular expressions all match a string containing a single monetary amount and nothing else. It's not clear from the question if that's the intent.
EDIT 3 To allow numbers that have no decimal part, or only one decimal digit, change it like this:
^\s*(?:[1-9]\d{0,2}(?:\.\d{3})*|0)(?:,\d{1,2})?$

I would give this regex a try:
\d+(?:\.\d{3})*?,\d{2}
What it says is:
- match digits until
a. a dot followed by 3 digits is found (and this step can be repeated several times)
b. or a comma followed by 2 digits is found
EDIT:
- thanks for the comments, I forgot about the constraint for the first value
updated regex
\d{1,3}(?:\.\d{3})*?,\d{2}

Complementing Mark's reply:
Who needs "." in the string and not "," to count cents. And need find the values in middle a text :
(?:[1-9]\d{0,2}(?:\,\d{3})*|0)(?:.\d{1,2})?
https://regexr.com/61166