I am trying to learn regex for my project I am working on to use it for input validation because I have been told that using regex is one of the best ways to do input validation.
So, I am trying to make sure a string contains an unknown number of coordinates which are separated by a space. An example of what the input will look like is 2,2 23.45,6 45,21.65 2,2 I'm not sure if it matters, but the last coordinate will always match the first. There can't be any symbols or extraneous spaces or commas. Only a decimal numbers split with a comma, followed by a space or an endline character.
I realize that this is probably quite a complex expression, and I am pretty much jumping into regex blind, so any help with this would be really appreciated. I am programming in c++ if that changes anything. Thanks.
EDIT:
I had forgotten about the possibility of negative numbers and newline characters. I also accept negative numbers and newline characters in the input.
So the input -2.3,2 34,-2 -2.3,2\n is acceptable. Thank you to everyone so far for the help.
You can try this regex:
^\d+(?:\.\d+)?,(?:\d+(?:\.\d+)? \d+(?:\.\d+)?,)*\d+(?:\.\d+)?$
Demo here:
Regex101
Note: The regex \d+(?:\.\d+)? matches any number, possibly having a decimal component. The ?: inside the parenthesis marks the quantity as a non capture group. This tells the regex engine to not capture what is inside, as we don't want to actually capture anything here. This possibly will result in a more efficient regex.
Related
I'm hoping we have some regular expression guru's here that might be able to help me - a regex newbie - solve a problem.
I know some people will want to know some background info on this issue:
Regex Flavor: Basic Regex, being used in a Vertica Database using the REGEXP_REPLACE function.
The regex I am using is working great with one exception.
I have a rule that I'm trying to implement, related to stripping the numbers from text, where any number that is part of a word, e.g. table5, go2market, 33monroe, room222, etc. is ignored and NOT filtered.
Here is what I started with for detecting numbers:
[-+]?[0-9]*\.?[0-9]
That seems to work pretty well, including handling directly adjacent commas and parentheses for example.
But all cases where there is a number that is part of alphabetic text is also being detected, which fails the rule that it cannot be a part of a word, and by word, I mean any alphabetic text.
So, in searching for solutions, I happened upon this regex that seems to work well detecting those specific cases where numbers appear next to, or in, any string of characters:
((?:[a-zA-Z]+[0-9]|[0-9]+[a-zA-Z])[a-zA-Z0-9]*)
My thought was that maybe I could add this as an INVERTED match to my original regex, to allow it to still select standalone numbers while ignoring those that were a part of a word, like so:
[-+]?[0-9]^((?:[a-zA-Z]+[0-9]|[0-9]+[a-zA-Z])[a-zA-Z0-9]*)*\.?[0-9]^((?:[a-zA-Z]+[0-9]|[0-9]+[a-zA-Z])[a-zA-Z0-9]*)
Unfortunately however, it breaks the original detection of standalone numbers.
:(
I'm hoping there is someone here that can spot what I'm doing wrong, and help me identify the right solution?
Thanks in advance!
According to Vertica documentation, the regex flavour seems to follow the Perl syntax. In this case you can use negative lookarounds and in particular a negative lookbehind: (?<!\w) (not preceded with a word character.)
Lookarounds are only tests and don't consume characters.
You can also use a negative lookahead to test the right part, (?!\w) (not followed by a word character), but it's more simple to use a word boundary since the pattern ends with a digit (that is also a word character):
(?<!\w)[-+]?\d*\.?\d+\b
In the worst case, if you have something like v1.0 in your string and you want to avoid it, you can try to use the bactracking control verbs (*SKIP) and (*FAIL). (*FAIL) forces the pattern to fail and (*SKIP) skips all the already matched positions before it. I hope vertica supports these Perl regex features.
Something like:
\p{L}+[-+]?\d*\.?\d+(*SKIP)(*FAIL)|[-+]?\d*\.?\d+(*SKIP)(?!\p{L})
I'm looking for a way to use regex to search for obviously false phone numbers that have the same digit repeating. The numbers are all formatted and stored as follows:
(111)111-1111
I'm not able to alter the text in any way.
I've tried modifying a few of the regex lines I've seen such as:
^([0-9])\1{2}.\1{3}.\1{4}$
which was for finding repeating digits with a period in between the numbers. However, I haven't figured out how to get around the first character as a parenthesis.
Any help would be appreciated!
You misunderstand the purpose of the . Dot Operator. It is not to match a period, it matches anything. In that (quite badly) regex, it serves only to skip the - – and because it matches anything, it will also match something like 11121113111.
Use this regexp instead:
^\(?([0-9])\1{2}\)?\1{3}-?\1{4}$
This checks for parentheses around the first group, optionally so it will still work without; and specifically checks for the presence of a dash between the second and third group of digits, also optionally.
Recently I'm writing/testing regexps on https://regex101.com/.
My question is: Is it possible to do a positive look-ahead AND a replacement in the same "replacement"? Or just limited kind of replacement is possible.
Input is several lines with phone numbers. Let's say the correct phone number where the number of "numbers" are 11. No matter how the numbers are divided/group together with - / characters, no matter if starts with + 00 or it is omitted.
Some example lines:
+48301234567
+48/30/1234567
+48-30-12-345-67
+483011223344556677
0048301234567
+(48)30/1234567
Positive look-ahead able to check if from the beginning until the end of line there are only 11 digits, regardless how many other, above specified character separating them. This works perfectly.
Where the positive look-ahead check is fine, I would like to delete every character but numbers. The replacement works fine until I'm not involving look-ahead.
Checking the regexp itself working perfectly ("gm" modes):
^(?:\+|00)?(?:[\-\/\(\)]?\d){11}$
Checking the replace part works perfectly (replace to nothing):
[^\d\n]
Put this into look-ahead, after the deletion of non new-line and non-digit characters from the matching lines:
(?=^(?:\+|00)?(?:[\-\/\(\)]?\d){11}$)[^\d\n]
Even I put the ^ $ into look-ahead, seems the replacement working only from beginning of the lines until the very first digit.
I know in real life the replacement and the check should/would go separate ways, however I'm curious if I could mix look-ahead/look-behind with string operations like replace, delete, take the string apart and put together as I like.
UPDATE: This is what would do the trick, however I feel this one "ugly" a bit. Is there any prettier solution?
https://regex101.com/r/yT5dA4/2
Or the version which I asked originally, where only digits remains: regex101.com/r/yT5dA4/3
You cannot replace/delete text with regex. Regex is just a tool for matching certain strings and then taking certain action depending on the matching text, eg. perform a substitution, retrieve the second capture group.
However it is possible to perform certain decisions within a regex engine, by using conditionals. The common syntax for this, with a lookahead assertion, is (?(?=regex)then|else).
With conditionals you can change the behaviour depending on how the text matches the regex. For your example you could do something like:
^(\+)?(?(1)\(|\d)
If the phone number starts with a plus it must be followed by a bracket, else it should start with a digit. Although in your situation, this is not very useful.
If you want to read up more on conditionals in regex you can do so here.
I need to parse an array-like text with regular expression and get the match groups.
One example of then text I want to parse is this:
['red','green', 'blue']
I want to use match groups, because I want to extract them.
I am using this regular expression, but the groups found by it are not like what I expected:
\[ *('.+?')( *, *('.+?'))* *\]
The idea is to parse in this order:
A square bracket
Any number of spaces
A group with:
Single quote
Any character
Single quote
Zero or more groups of:
Any number of spaces
A comma
Any number of spaces
A group with
Single quote
Any character
Single quote
Any number of spaces
A square bracket
And get one group with each parsed array element.
Can you help me?
Hint: a easy way to test regexp is the site http://rubular.com
This isn't going to be a totalitarian answer, but I'm fairly certain you can't whitespace check by doing " *", at least it may depend on the language you're using.
Here's a C# regex example that shows some of the language requirements to check for whitespace: regex check for white space in middle of string
Edit: I see you added Ruby as your language, unfortunately I'm not verbose in Ruby so specifics I cannot help you with, sorry.
Edit2: Seeing as you're forcing yourself into Ruby to debug your regex statement, might I suggest: http://www.debuggex.com/ which tries to stay language independent?
Try this regex: '([^']+)', it should give you the following match groups red, green, blue according to rubular.com
You can match an arbitrary number of groups with one regex:
^\[\s*|(?:\G'([^']+)'\s*(?:,\s*|]$))+
or like this (should be more performant):
^\[\s*+|(?>\G'([^']++)'\s*+(?>,\s*+|]$))++
This work in ruby like asked before, in delphi I don't know.
So I wanted to limit a textbox which contains an apartment number which is optional.
Here is the regex in question:
([0-9]{1,4}[A-Z]?)|([A-Z])|(^$)
Simple enough eh?
I'm using these tools to test my regex:
Regex Analyzer
Regex Validator
Here are the expected results:
Valid
"1234A"
"Z"
"(Empty string)"
Invalid
"A1234"
"fhfdsahds527523832dvhsfdg"
Obviously if I'm here, the invalid ones are accepted by the regex. The goal of this regex is accept either 1 to 4 numbers with an optional letter, or a single letter or an empty string.
I just can't seem to figure out what's not working, I mean it is a simple enough regex we have here. I'm probably missing something as I'm not very good with regexes, but this syntax seems ok to my eyes. Hopefully someone here can point to my error.
Thanks for all help, it is greatly appreciated.
You need to use the ^ and $ anchors for your first two options as well. Also you can include the second option into the first one (which immediately matches the third variant as well):
^[0-9]{0,4}[A-Z]?$
Without the anchors your regular expression matches because it will just pick a single letter from anywhere within your string.
Depending on the language, you can also use a negative look ahead.
^[0-9]{0,4}[A-Za-z](?!.*[0-9])
Breakdown:
^[0-9]{0,4} = This look for any number 0 through 4 times at the beginning of the string
[A-Za-z] = This look for any characters (Both cases)
(?!.*[0-9]) = This will only allow the letters if there are no numbers anywhere after the letter.
I haven't quite figured out how to validate against a null character, but that might be easier done using tools from whatever language you are using. Something along this logic:
if String Doesn't equal $null Then check the Rexex
Something along those lines, just adjusted for however you would do it in your language.
I used RegEx Skinner to validate the answers.
Edit: Fixed error from comments