We Keep Coding

Regular expression that works on dots

I have this regular expression :
string[] values = Regex
.Matches(mystring4, #"([\w-[\d]][\w\s-[\d]]+)|([0-9]+)")
.OfType<Match>()
.Select(match => match.Value.Trim())
.ToArray();
This regular expression turns this string :
MY LIMITED COMPANY (52100000 / 58447000)";
To these strings :
MY LIMITED COMPANY - 52100000 - 58447000
This also works on non-English characters.
But there is one problem, when I have this string : MY. LIMITED. COMPANY. , it splits that too. I don't want that. I don't want that regular expression to work on dots. How can I do that? Thanks.

You may add the dot after each \w in your pattern, and I also suggest removing unnecessary ( and ):
string[] values = Regex
.Matches("MY. LIMITED. COMPANY. (52100000 / 58447000)", #"[\w.-[\d]][\w.\s-[\d]]+|[0-9]+")
.OfType<Match>()
.Select(match => match.Value.Trim())
.ToArray();
foreach (var s in values)
Console.WriteLine(s);
See the C# demo
Pattern:
[\w.-[\d]] - one Unicode letter or underscore ([\w-[\d]]) or a dot (.)
[\w.\s-[\d]]+ - 1 or more (due to + quantifier at the end) characters that are either Unicode letters or underscore, ., or whitespace (\s)
| - or
[0-9]+ - one or more ASCII-only digits

I'd simplify the expression. What if the names in the front include numbers? Not that my solution doesn't exactly mimic the original expression. It will allow numbers in the name part.
Let's start from the beginning:
To match words all you need is a sequence of word characters:
\w+
This will match any alphanumerical characters including underscores (_).
Considering you want the possibility of the word ending with a dot, you can add it and make it optional (one or zero matches):
\w+\.?
Note the escape to make it an actual character rather than a character class "any character".
To match another potential word following, we now simply duplicate this match, add a white space before, and once again make it optional using the * quantifier:
\w+\.?(?:\w+\.?)*
In case you haven't seen a group starting with ?: is a non-matching group. In essence this works like a usual group, but won't save a matching group in your results.
And that's it already. This pattern will split your demo string as expected. Of course there could be other possible characters not being covered by this.
You can see the results of this matching online here and also play around with it.
To test your regular expressions (and to learn them), I'd really recommend you using a tool such as http://regex101.com
It has an input mask allowing you to provide your pattern and your target string. On the right hand side it will first explain the pattern to you (to see if it's indeed what you had in mind) and below it will show all the groups matched. Just keep in mind it actually uses slightly different flavors of regular expressions, but this shouldn't matter for such simple patterns. (I'm not affiliated with that site, just consider it really useful.)
As an alternative, to directly use C#'s regex parser, you can also try this Regex Tester. This works in a similar way, although doesn't include any explanations, which might be not as ideal for someone just getting started.

Extract string from a pattern preceded by any length

I'm looking for a regular expression to extract a string from a file name
eg if filename format is "anythingatallanylength_123_TESTNAME.docx", I'm interested in extracting "TESTNAME" ... probably fixed length of 8. (btw, 123 can be any three digit number)
I think I can use regex match ...
".*_[0-9][0-9][0-9]_[A-Z][A-Z][A-Z][A-Z][A-Z][A-Z][A-Z][A-Z].docx$"
However this matches the whole thing. How can I just get "TESTNAME"?
Thanks

Use parenthesis to match a specific piece of the whole regex.
You can also use the curly braces to specify counts of matching characters, and \d for [0-9].
In C#:
var myRegex = new Regex(#"*._\d{3}_([A-Za-z]{8})\.docx$");
Now "TESTNAME" or whatever your 8 letter piece is will be found in the captures collection of your regex after using it.
Also note, there will be a performance overhead for look-ahead and look-behind, as presented in some other solutions.

You can use a look-behind and a look-ahead to check parts without matching them:
(?<=_[0-9]{3}_)[A-Z]{8}(?=\.docx$)
Note that this is case-sensitive, you may want to use other character classes and/or quantifiers to fit your exact pattern.

In your file name format "anythingatallanylength_123_TESTNAME.docx", the pattern you are trying to match is a string before .docx and the underscore _. Keeping the thing in mind that any _ before doesn't get matched I came up with following solution.
Regex: (?<=_)[A-Za-z]*(?=\.docx$)
Flags used:
g global search
m multi-line search.
Explanation:
(?<=_) checks if there is an underscore before the file name.
(?=\.docx$) checks for extension at the end.
[A-Za-z]* checks the required match.
Regex101 Demo

Thanks to #Lucero #noob #JamesFaix I came up with ...
#"(?<=.*[0-9]{3})[A-Z]{8}(?=.docx$)"
So a look behind (in brackets, starting with ?<=) for anything (ie zero or more any char (denoted by "." ) followed by an underscore, followed by thee numerics, followed by underscore. Thats the end of the look behind. Now to match what I need (eight letters). Finally, the look ahead (in brackets, starting with ?=), which is the .docx
Nice work, fellas. Thunderbirds are go.

Foreign language characters in Regular expression in C#

In C# code, I am trying to pass chinese characters: " 中文ABC123".
When I use alphanumeric in general using "^[a-zA-Z0-9\s]+$",
it doesn't pass for "中文ABC123" and regex validation fails.
What other expressions do I need to add for C#?

To match any letter character from any language use:
\p{L}
If you also want to match numbers:
[\p{L}\p{Nd}]+
\p{L} ... matches a character of the unicode category letter.
it is the short form for [\p{Ll}\p{Lu}\p{Lt}\p{Lm}\p{Lo}]
\p{Ll} ... matches lowercase letters. (abc)
\p{Lu} ... matches uppercase letters. (ABC)
\p{Lt} ... matches titlecase letters.
\p{Lm} ... matches modifier letters.
\p{Lo} ... matches letters without case. (中文)
\p{Nd} ... matches a character of the unicode category decimal digit.
Just replace: ^[a-zA-Z0-9\s]+$ with ^[\p{L}0-9\s]+$

Thanks to #Andie2302 for pointing to the right way to do it.
In Addition, for many language in the world, it's still has the 'addition character' that require main character to generate it (ex. Thai word 'เก็บ' if use only \p{L} it will display only 'เกบ', you can see that some symbolic will be missing from the word).
That's why only \p{L} will not work for all foreign language.
So, you need to use code below, to support almost foreign language
\p{L}\p{M}
NOTE:
L stand for 'Letter' (All letter from all language, but does not include the 'Mark')
M stand for 'Mark' (The 'Mark' cannot display alone, it require 'Letter' to display it)
In Addition that you need Number, use code below
\p{N}
NOTE:
N stand for 'Numeric'
Thanks to this website for very useful information
https://www.regular-expressions.info/unicode.html

Regex validation Comma Separated Words - Foreign Charcters

I am developing an application in Arabic-English language, so i needed a Regex that validates to a set of separated words, here is my RegEx:
^([a-zA-Z]+(,[a-zA-Z]+)*)?$
This works flawless for me but as you see the charters specified is in English, i want this for Arabic language.
Can this expression be altered to accept other charters either Arabic or even maybe some other language ?

Instead of restricting to a set of alphabetical character, exclude the characters that mark the end of your word.
^([^,]+(,[^,]+)*)?$
If you really want to match Arabic characters, see: regular expression For Arabic Language

Regular expression to catch letters beyond a-z

A normal regexp to allow letters only would be "[a-zA-Z]" but I'm from, Sweden so I would have to change that into "[a-zåäöA-ZÅÄÖ]". But suppose I don't know what letters are used in the alphabet.
Is there a way to automatically know what chars are are valid in a given locale/language or should I just make a blacklist of chars that I (think I) know I don't want?

You can use \pL to match any 'letter', which will support all letters in all languages. You can narrow it down to specific languages using 'named blocks'. More information can be found on the Character Classes documentation on MSDN.
My recommendation would be to put the regular expression (or at least the "letter" part) into a localised resource, which you can then pull out based on the current locale and form into the larger pattern.

What about \p{name} ?
Matches any character in the named character class specified by {name}.
Supported names are Unicode groups and block ranges. For example, Ll, Nd, Z,
IsGreek, IsBoxDrawing.
I don't know enough about unicode, but maybe your characters fit a unicode class?

See character categories selection with \p and \w unicode semantics.

All chars are "valid," so I think you're really asking for chars that are "generally considered to be letters" in a locale.
The Unicode specification has some guidelines, but in general the answer is "no," you would need to list the characters you decide are "letters."

Is there a way to automatically know what chars are are valid in a given locale/language or should I just make a blacklist of chars that I (think I) know I don't want?
This is not, in general, possible.
After all Engligh text does include some accented characters (e.g. in "fête" and "naïve" -- which in UK-English to be strictly correct still use accents). In some languages some of the standard letters are rarely used (e.g. y-diaeresis in French).
Then consider including foreign words are included (this will often be the case where technical terms are used). Quotations would be another source.
If your requirements are sufficiently narrowly defined you may be able to create a definition, but this requires linguistic experience in that language.

This regex allows only valid symbols through:
[a-zA-ZÀ-ÿ ]