I'm developing new specific syntax. Within it there are two kinds of code:
I: = or + or - (one or several plus, minus or equal signs in a row);
Regex for that is /[+=-]+/.
II: 6:+ or 15:- or 999:= (any integer, followed by one plus, minus or equal sign);
Regex for that is /\d+:[+=-]/.
In one entry there may be any amount of any of these tokens.
Each new entry has to be surrounded by brackets: [code here].
Kinds of code in brackets may stand next to each other: [=6:+-] or [15:-++=3:+] etc.
Empty entries are not allowed.
So, I can't make a regex to match proper entries!
I've tried this one /\[([=+-]*(\d+:[=+-])?[=+-]*)\]/, but it matches [] as well, while it is an еггог.
MATCH any of those
[=] [---] [+=-] [=+-] [17:=] [==+-] [6:=-] [+5:=-]
[==-=+] [+=====-] [15:-++=3:+] [=======] [+=-+==-] [---==--] [==-=+==] [=--==--]
NO MATCH
[] [=:1] [:2+] [3-:]
I dont know what flavor of regex but this should work for pretty much all of them:
\[((?:[+=-]+|[+=-]?\d+:[+=-]+)+)\]
Debuggex Demo
It makes use of | or operand, so it either captures one kind of match (the collection of -+= signs or the numbers with colons and such)
Also, it seems that since you want [+5:=-] to match, I added a [+-]? to match for that.
EDIT:
This allows for multiple occurrences of the language. This, however, may be trivial as there is nothing to distinguish between separate parts of code.
OMG, it could be way more simple:
\[(?:(?:\d+:)?[+=-])+\]
I can't believe I was so stupid.
Related
I need to create a regular expression to validate a strong password in my MVC Model. Here are the rules that I need to apply:
Min 7 characters
Max 15 characters
At least 3 out of 4 different types of characters.
Numbers
Lowercase
Uppercase
Special (viz. !##$%&/=?_.)
Here's what I have tried so far:
[DataType(DataType.Password)]
[RegularExpression("([a-z]|[A-Z]|[0-9]|[\\W]){4}[a-zA-Z0-9\\W]{3,11}", ErrorMessage = "Invalid password format")]
public string Password { get; set; }
Creating a regex that will find any number of different kinds of character classes in any order is a little challenging because as soon as you match a character, it's already captured and you can't back it up. However, the .NET regex engine supports lookahead expressions. Therefore, you can check to make sure that a string contains something without actually capturing any of the string. For instance, let's say that you want to find any 10 character long string that contains at least one instance of the letter "J". You could do that easily with a lookahead expression, like this:
(?=.*J).{10}
The (?=) construct declares a lookahead pattern. The pattern it looks for is .*J, which means that, starting at the current position, there can be any number of any character followed by a letter "J". If anything comes after the J, that's fine, it will still match. However, since it's a lookahead, none of those characters were actually captured, so then the .{10} capturing part of the pattern picks up from the original position and matches from there. Since the lookaheads don't move the position at all, you can put multiple of them in a row without consequence, so you can do something like this:
^(?=.*[A-Z])(?=.*\d)(?=.*[a-z])(?=.*\W).{7,15}$
As far as applying only three of the four character class rules, the only way I can think of to do that would be to list all of the combinations (e.g. for two of the three rules A, B, and C, you could match AB|AC|BC) . So for instance, if you were only concerned with two of the three (uppercase, lowercase, and digits, for instance), you could structure your lookaheads like this:
(?:(?=.*[A-Z])(?=.*\d)|(?=.*[A-Z])(?=.*[a-z])|(?=.*\d)(?=.*[a-z]))
Making it support there out of four would just be a matter of making the list of options even longer...
A development of Steven's answer would be to test for all possible combinations of the types:
^((?=.*[A-Z])(?=.*\d)(?=.*[a-z])|(?=.*[A-Z])(?=.*\d)(?=.*[!##$%&\/=?_.-])|(?=.*[A-Z])(?=.*[a-z])(?=.*[!##$%&\/=?_.-])|(?=.*\d)(?=.*[a-z])(?=.*[!##$%&\/=?_.-])).{7,15}$
Also using the given special characters.
In a more readable form
^((?=.*[A-Z])(?=.*\d)(?=.*[a-z])|
(?=.*[A-Z])(?=.*\d)(?=.*[!##$%&\/=?_.-])|
(?=.*[A-Z])(?=.*[a-z])(?=.*[!##$%&\/=?_.-])|
(?=.*\d)(?=.*[a-z])(?=.*[!##$%&\/=?_.-])).{7,15}$
Test for either of the possible four combinations of types and make sure there are 7-14 of them.
Regards
I am very new to regex and regular expressions, and I am stuck in a situation where I want to apply a regex on an JSF input field.
Where
alphanumeric
multiple spaces
multiple dot(.)
multiple hyphen (‐)
are allowed, and Minimum limit is 1 and Maximum limit is 5.
And for multiple values - they must be separated by comma (,)
So a Single value can be:
3kd-R
or
k3
or
-4
And multiple values (must be comma separated):
kdk30,3.K-4,ER--U,2,.I3,
By the help of stackoverflow, so far I am able to achieve only this:
(^[a-zA-Z0-9 ]{5}(,[a-zA-Z0-9 ]{5})*$)
Something like
^[-.a-zA-Z0-9 ]{1,5}(,[-.a-zA-Z0-9 ]{1,5})*$
Changes made
[-.a-zA-Z0-9 ] Added - and . to the character class so that those are matched as well.
{1,5} Quantifier, ensures that it is matched minimum 1 and maximum 5 characters
Regex demo
You've done pretty good. You need to add hyphen and dot to that first character class. Note: With the hyphen, since it delegates ranges within a character class, you need to position it where contextually it cannot be specifying a range--not to say put it where it seems like it would be an invalid range, e.g., 7-., but positionally cannot be a range, i.e., first or last. So your first character class would look something like this:
[a-zA-Z 0-9.-]{1,5} or [-a-zA-Z0-9 .]{1,5}
So, we've just defined what one segment looks like. That pattern can reoccur zero or more times. Of course, there are many ways to do that, but I would favor a regex subroutine because this allows code reuse. Now if the specs change or you're testing and realize you have to tweak that segment pattern, you only need to change it in one place.
Subroutines are not supported in BRE or ERE, but most widely-used modern regex engines support them (Perl, PCRE, Ruby, Delphi, R, PHP). They are very simple to use and understand. Basically, you just need to be able to refer to it (sound familiar? refer-back? back-reference?), so this means we need to capture the regex we wish to repeat. Then it's as simple as referring back to it, but instead of \1 which refers to the captured value (data), we want to refer to it as (?1), the capturing expression. In doing so, we've logically defined a subroutine:
([a-zA-Z 0-9.-]{1,5})(,(?1))*
So, the first group basically defines our subroutine and the second group consists of a comma followed by the same segment-definition expression we used for the first group, and that is optional ('*' is the zero-or-more quantifier).
If you operate on large quantities of data where efficiency is a consideration, don't capture when you don't have to. If your sole purpose for using parenthesis is to alternate (e.g., \b[bB](asset|eagle)\b hound) or to quantify, as in our second group, use the (?: ... ) notation, which signifies to the regex engine that this is a non-capturing group. Without going into great detail, there is a lot of overhead in maintaining the match locations--not that it's complex, per se, just potentially highly repetitive. Regex engines will match, store the information, then when the match fails, they "give up" the match and try again starting with the next matching substring. Each time they match your capture group, they're storing that information again. Okay, I'm off the soapbox now. :-)
So, we're almost there. I say "almost" because I don't have all the information. But if this should be the sole occupant of the "subject" (line, field, etc.--the data sample you're evaluating), you should anchor it to "assert" that requirement. The caret '^' is beginning of subject, and the dollar '$' is end of subject, so by encapsulating our expression in ^ ... $ we are asserting that the subject matches in it's entirety, front-to-back. These assertions have zero-length; they consume no data, only assert a relative position. You can operate on them, e.g., s/^/ / would indent your entire document two spaces. You haven't really substituted the beginning of line with two spaces, but you're able to operate on that imaginary, zero-length location. (Do some research on zero-length assertions [aka zero-width assertions, or look-arounds] to uncover a powerful feature of modern regex. For example, in the previous regex if I wanted to make sure I did not insert two spaces on blank lines: s/^(?!$)/ /)
Also, you didn't say if you need to capture the results to do something with it. My impression was it's validation only, so that's not necessary. However, if it is needed, you can wrap the entire expression in capturing parenthesis: ^( ... )$.
I'm going to provide a final solution that does not assume you need to capture but does assume the entire subject should consist of this value:
^([a-zA-Z 0-9. -]{1,5})(?:,(?1))*$
I know I went on a bit, but you said you were new to regex, so wanted to provide some detail. I hope it wasn't too much detail.
By the way, an excellent resource with tutorials is regular-expressions dot info, and a wonderful regex development and testing tool is regex101 dot com. And I can never say enough about stack overflow!
I've moved to emacs recently and I am used to/like numbers being highlighted. A quick hack I took from here puts the following in my .emacs:
(add-hook 'after-change-major-mode-hook
'(lambda () (font-lock-add-keywords
nil
'(("\\([0-9]+\\)"
1 font-lock-warning-face prepend)))))
Which gives a good start, i.e. any digit is highlighted. However, I am a complete beginner with regex and would ideally like the following behaviour:
Also highlight the decimal point if it's part of a float, e.g. 12.34
Do not highlight any part of the number if it is next/part of a word. e.g. in these cases: foo11 ba11r 11spam, none of the '1's should be highlighted
Allow 'e' within two number integers to allow scientific notation (not required, bonus credit)
Unfortunately this looks very much like a 'do this for me' question which I am loathe to post, but I have failed thus far to make any decent progress myself.
About as far as I have got is discovering [^a-zA-Z][0-9]+[^a-zA-Z] to match anything but a letter either side (e.g. an equals sign), but all this does is include the adjacent symbol in the highlighting. I am not sure how to tell it 'only highlight the numbers if there isn't a letter on either side'.
Of course, I can't imagine regex is the way to go with complicated syntax highlighting, so any good number highlighting in emacs ideas are also welcome,
Any help very much appreciated. (In case it makes any difference, this is for use when Python coding.)
Start by going to your scratch buffers and typing in a some test text. put some numbers in there, some identifiers that contain numbers, some numbers with missing parts (like .e12), etc. These will be our testcases and will let us experiment rapidly. Now run M-x re-builder to enter the regex builder mode, which will let you try out any regex against the text of the current buffer to see what it matches. This is a very handy mode; you'll be able to use it all the time. Just note that because Emacs lisp requires you to put regexes into strings, you must double up on all of your backslashes. You're already doing that correctly, but I'm not going to double them up in here.
So, limiting the match to numbers that are not part of identifiers is pretty easy. \b will match word boundaries, so putting one at either end of your regex will make it match a whole word
You can match floats just by adding a period to the character class you started with, so that it becomes [0-9.]. Unfortunately, that can match a period all on it's own; what we really want is [0-9]*\.?[0-9]+, which will match 0 or more digits followed by an optional period followed by one or more digits.
A leading sign can be matched with [-+]?, so that gets us negative numbers.
To match exponents we need an optional group: \(...\)?, and since we are only using this for highlighting, and don't actually need to separate out the content of the group, we can do \(?:...\), which will save the regex matcher a little time. Inside the group we will need to match an "e" ([eE]), an optional sign ([-+]?), and one or more digits ([0-9]+).
Putting it all together: [-+]?\b[0-9]*\.?[0-9]+\(?:[eE][-+]?[0-9]+\)?\b. Note that I've put the optional sign before the first word boundary, because the "+" and "-" characters create a word boundary.
First of all, lose the add-hook and the lambda. The font-lock-add-keywords call doesn't need either. If you want this only for python-mode, pass the mode symbol as the first argument instead of nil.
Second, there are two main ways to do that.
Add a grouping construct around the digits. The numbers in the font-lock-keywords forms correspond to the groups, so this would be '(("\\([^a-zA-Z]\\([0-9]+\\)[^a-zA-Z]\\)" 2 font-lock-warning-face prepend). The outer grouping is rather useless here, though, so this can be simplified to '(("[^a-zA-Z]\\([0-9]+\\)[^a-zA-Z]" 1 font-lock-warning-face prepend).
Just use the beginning and end of symbol backslash constructs. Then the regexp looks like this: \_<[0-9]+\_>. We can highlight the whole match here, so there's no need for the group number: '(("\\_<[0-9]+\\_>" . font-lock-warning-face prepend). As a variation, you could use the beginning-of-word and end-of-word constructs, but you probably don't want to highlight numbers adjacent to underscores or whatever other characters, if any, python-mode has in the syntax class symbol.
And lastly, there's probably no need for prepend. The numbers are likely all unhighlighted before this, and if you consider possible interaction with other minor modes like whitespace, you'd better choose append, or just omit this element entirely.
End result:
(font-lock-add-keywords nil '(("\\_<[0-9]+\\_>" . font-lock-warning-face)))
One of my homework questions asked to develop a regex for all strings over x,y,z that did not contain xxx
After doing some reading I found out about negative lookahead and made this which works great:
(x(?!xx)|y|z)*
Still, in the spirit of completeness, is there anyway to write this without negative lookahead?
Reading I have done makes me think it can be done with some combination of carets (^), but I cannot get the right combination so I am not sure.
Taking it a step further, is it possible to exclude a string like xxx using only the or (|) operator, but still check the strings in a recursive fashion?
EDIT 9/6/2010:
Think I answered my own question. I messed with this some more, trying make this regex with only or (|) statements and I am pretty sure I figured it out... and it isn't nearly as messy as I thought it would be. If someone else has time to verify this with a human eye I would appreciate it.
(xxy|xxz|xy|xz|y|z)*(xxy|xxz|xx|xy|xz|x|y|z)
Try this:
^(x{0,2}(y|z|$))*$
The basic idea is this: for match at most 2 X's, followed by another letter or the end of the string.
When you reach a point where you have 3 X's, the regex has no rule that allows it to keep matching, and it fails.
Working example: http://rubular.com/r/ePH0fHlZxL
A less compact way to write the same is (with free spaces, usually the /x flag):
^(
y| # y is ok
z| # so is z
x(y|z|$)| # a single x, not followed by x
xx(y|z|$) # 2 x's, not followed by x
)*$
Based on the latest edit, here's an ever flatter version of the pattern: I'm not entirely sure I understand your fascination with the pipe, but you can eliminate some more options - by allowing an empty match on the second group you don't need to repeat permutations from the first group. That regex also allows ε, which I think is included in your language.
^(xxy|xxz|xy|xz|y|z)*(xx|x|)$
Basically you have the right answer already - well done you. :)
Carat (^) in a set [^abc] will only match where it does not find a character in that set so it's application for matching orders of characters (i.e. strings) is limited and weak.
Regex has numeric quantifiers {n} and {a,b} which allow you to match a defined number of repititions of a pattern, which would work for this specific pattern (because it's 'x' repeated) but it's not particularily expressive of the problem you're trying to solve (even for regex!) and is a bit brittle (it wouldn't be appropriate for negative match 'xyx' for example.
An or pattern again would be verbose and rather unexpressive but it could be done as the fragment:
(x|xx)[^x] // x OR xx followed by NOT x
Obviously you can do this with an iterative algorithm but that's highly inefficient compared to a regex.
Well done for thinking beyond the solution though.
I know you don't want to use lookahead, but here's another way to solve this:
^(?:(?!xxx)[xyz])*$
will match any line of characters x, y or z as long as it doesn't contain the string xxx.
I'm looking for some regex code that I can use to check for a valid username.
I would like for the username to have letters (both upper case and lower case), numbers, spaces, underscores, dashes and dots, but the username must start and end with either a letter or number.
Ideally, it should also not allow for any of the special characters listed above to be repeated more than once in succession, i.e. they can have as many spaces/dots/dashes/underscores as they want, but there must be at least one number or letter between them.
I'm also interested to find out if you think this is a good system for a username? I've had a look for some regex that could do this, but none of them seem to allow spaces, and I would like for the usernames to have some spaces in them.
Thank you :)
So it looks like you want your username to have a "word" part (sequence of letters or numbers), interspersed with some "separator" part.
The regex will look something like this:
^[a-z0-9]+(?:[ _.-][a-z0-9]+)*$
Here's a schematic breakdown:
_____sep-word…____
/ \
^[a-z0-9]+(?:[ _.-][a-z0-9]+)*$ i.e. "word ( sep word )*"
|\_______/ \____/\_______/ |
| "word" "sep" "word" |
| |
from beginning of string... till the end of string
So essentially we want to match things like word, word-sep-word, word-sep-word-sep-word, etc.
There will be no consecutive sep without a word in between
The first and last char will always be part of a word (i.e. not a sep char)
Note that for [ _.-], - is last so that it's not a range definition metacharacter. The (?:…) is what is called a non-capturing group. We need the brackets for grouping for the repetition (i.e. (…)*), but since we don't need the capture, we can use (?:…)* instead.
To allow uppercase/various Unicode letters etc, just expand the character class/use more flags as necessary.
References
regular-expressions.info/Anchors, Character Class, Repetition, Grouping
Although I'm sure someone will shortly post a 1 million lines regex to do exactly what you want, I don't think in this case a regex is a good solution.
Why don't you write a good old fashioned parser? It will take about as long as writing the regex that does everything you mentioned, but it's going to be much easier to maintain and read.
In particular, this is the tricky part:
it should also not allow for any of
the special characters listed above to
be repeated more than once in
succession
Alternatively you can always do a hybrid of the two. A regex for the other checks ([a-zA-Z0-9][a-zA-Z0-9 _-\.]*[a-zA-Z0-9]) and a non-regex method for the no-repeat requirement.
You don't have to use a regex for everything. I find that requirements like the "no two consecutive characters" usually make the regexes so ugly that it's better to do that bit with a simple procedural loop.
I'd just use something like ^[A-Za-z0-9][A-Za-z0-9 \.\-_]*[A-Za-z0-9]$ (or the equivalents like ::alnum:: if your regex engine is more advanced) and then just check every character in a loop to make sure the next character isn't the same.
By doing it procedurally, you can check all the other rules you're likely to want at some point without resorting to what I call "regex gymnastics", things like:
not allowed to contain your first or last name.
no more than two consecutive digits.
and so forth.