I currently have this regular expression:
/(^| )[a-z]{5}-[a-z]{5}( |$)/i
start of string or space, 5 letters, literal dash, 5 letters, space or end of string, case insensitive.
This finds a string that looks like this: pejnd-zxdgn
I need to allow the first letter only to be a digit instead of a letter.
How do I write this?
Edit:
To clarify
should match: pejnd-zxdgn or 7ejnd-zxdgn
Should not match 7pejnd-zxdgn or 7ejn-zxdgn or p7ejnd-zxdgn
Just add a pattern for digit before the [a-z] part. And change the quantifier to {4}:
/(^| )[0-9][a-z]{4}-[0-9][a-z]{4}( |$)/i
After your update, you just want the first character to be digit or character. Also, you can use word boundaries - \b at the beginning and the end, as noted in comments. So, change your regex to:
/\b[a-z0-9][a-z]{4}-[a-z]{5}\b/i
Related
This question already has an answer here:
Javascript Regex restrict underscore at start and end
(1 answer)
Closed 4 months ago.
I need to compose a regular expression for string, with a max length of 6 characters, containing only Latin letters in lowercase, with an optional underscore separator, without underscore starting and trailing.
I tried the following
^[a-z_]{1,6}$
But it allows underscore at the start and the end.
I also tried:
^([a-z]_?[a-z]){1,6}$
^(([a-z]+)_?([a-z]+)){1,6}$
^([a-z](?:_?)[a-z]){1,6}$
But nothing works. Please help.
Expecting:
Valid:
ex_bar
Not valid:
_exbar
exbar_
_test_
This is a fairly simple pattern that should work ^(?!_)[a-z_]{0,5}[a-z]$. See here for a breakdown.
I would express your requirement as:
^(?!.{7,}$)[a-z](?:[a-z_]*[a-z])*$
This pattern matches:
^ from the start of the string
(?!.{7,}$) assert that at most 6 characters are present
[a-z] first letter must be a-z
(?:[a-z_]*[a-z])* match a-z or underscore in the middle, but only a-z at the end
$ end of the string
Note that the behavior of the above pattern is that one character matches must be only letter a-z. Similarly, two character matches can also only be a-z twice. With three character matches and longer, it is possible for underscore to appear in the middle.
Here is a running demo.
(?!^_)([a-z_]{6})(?<!_$)
You could use a negative look-ahead and negative look-behind to ensure that the string doesn't start and end with an _ underscore.
https://regex101.com/r/sMho0c/1
How can I not allow a user to enter a word with repeating letters I already have the case for special characters?
I have tried this and it works for the special characters allowed in the text.
^(?!.*([ \-])\1)\w[a-zA-z0-9 \-]*$
3 My Address--
Will not work (--)
This is what I am trying to do for the letters (?!.*([a-z])\1{4}) but it does not work it breaks the regex.
(?!.*([ \-])\1)(?!.*([a-z])\1{4})\w[a-zA-z0-9 \-]*$
It should prevent any repeating letters when they have been entered 4 times in a row for example this is for a address and as it stand I can enter.
3 My Adddddddddd
You need to use \2 backreference in the second lookahead, and mind using [a-zA-Z], not [a-zA-z] in the consuming part:
^(?!.*([ -])\1)(?!.*([A-Za-z])\2{3})\w[a-zA-Z0-9 -]*$
See the regex demo.
The first capturing group is ([ -]) in the first lookahead, the second lookahead contains the second group, thus, \2 is necessary.
As you want to filter out matches with at least 4 identical consecutive letters, you need ([A-Za-z])\2{3}, not {4}.
Also, if you plan to match a digit at the beginning, consider replacing \w with \d.
Regex details
^ - start of string
(?!.*([ -])\1) - no two identical consecutive spaces or hyphens allowed in the string
(?!.*([A-Za-z])\2{3}) - no four identical consecutive letters allowed in the string
\w - the first char should be a letter, digit or _
[a-zA-Z0-9 -]* - 0+ letters, digits, spaces or hyphens
$ - end of string.
Hi guys have the following regex:
/([A-Z][\w-]*(\s+[A-Z][\w-]*)+)/
I've tried in different way, but i'm not a pro with regex..so, this is what want to do:
Add a rule that match only 3+ characters words.
Add a rule that can match name like "Institute of Technology" (so, three words with a lowercase word between the first and the last)
Can you help me to do that? (I should do different regex, am i right?)
In order to help you to understand, this is what you have:
[A-Z]: one character in the class A-Z
[\w-]*: a concatenation of zero or more word character or hypens
(...)+: one or more:
\s+: at least one space
[A-Z]: one character in the class A-Z
[\w-]*: a concatenation of zero or more word character or hypens
This is what you want:
[A-Z]: a capital letter
[\w-]*: a concatenation of zero or more word character or hypens
\s+: at least one space
[a-z]: a lower-case letter
[\w-]*: a concatenation of zero or more word character or hypens
\s+: at least one space
[A-Z]: a capital letter
[\w-]*: a concatenation of zero or more word character or hypens
That is:
[A-Z][\w-]*\s+[a-z][\w-]*\s+[A-Z][\w-]*
You may want to do some small changes. I think you can do them by your own.
A rule that matches only 3+ characters word is \w{3,}. If you want to capitalize the first character use [A-Z]\w{2,}.
(\w\w\w+)|(\w+ [a-z]+ \w+) - This code searches for a word consisting of at least 3 letters OR a word with at least 1 sign, space, small letters, 1+ signs. You can switch \w with [A-Z] if necessary.
If your 3 word phrase has to have 2 words with capital letters, change the second brackets to ([A-Z]\w* [a-z]+ [A-Z]\w*). Try it here: https://regex101.com/r/E3IPTj/1
Not sure on the scope of your limitations but a few 'building blocks' might help. Also id suggest just starting at the beginning I don't know any recent websites that handle learning regex well but when I started I used the following http://www.regular-expressions.info/tutorial.html (It's been many years, and the website does reflect its age so to speak)
However onto your regex:
Following your example: Institute of Technology
You need to know just a few things, character sets (and how to use matching length) and the space.
Character sets match one length (by default) and are done like for example [abc] that will match a, b, or c, and also supports character ranges (a-z)/grouped (eg. \d all digits).
The match length can be changed by using the:
+ - one or more (examples: a+, [abc]+, \d+)
* - zero or more (examples: a*, [abc]*)
And this one you might want but thats up to you
{min, max} - specific range, eg. b{3,5} will match 3-5 joined 'b' characters (bbb, bbbb, bbbbb) max can be omitted `{min,} to have at least min chars but no max
Spaces are done using "" (a space), (\s matches any whitespace character (equal to [\r\n\t\f\v ]) (spaces, tabs, newlines, ...)
In your example its a matter of case sensitive or not if not case sensitive we can use a simple [A-Za-z]+ to match upper and lowercase a-z of at least one length, together with the space we get something along the lines of
/[A-Za-z]+ [A-Za-z]+ [A-Za-z]+/
It's that simple. For case insensitive matching there is also an option flag, we can use i which will result in
/[a-z]+ [a-z]+ [a-z]+/i
If you do want to have case sensitive matching you will need to separate them how you like:
/[A-Z][a-z]* [a-z]+ [A-Z][a-z]*/ // (*A a A*)
As a small change I've also changed + into * so the lowercase part is not required, again up to you.
Also note that to match the beginning of a string your required to use ^ and to match the end of a string use $ the above examples will match any segment, not the whole input eg: qhg8Institute of Technology8tghagus would work
So final result:
/^[A-Z][a-z]* [a-z]+ [A-Z][a-z]*$/ // case sensitive (Aa a Aa)
/^[a-z]+ [a-z]+ [a-z]+$/i // case insensitive
Obviously there is lots more to learn that can be used to expand/ optimize this but regex are so customizable its really up to the person needing them to specify his/ her limitations/ requirements.
As a side note I noticed people using \w for word chars, but this also includes digits, _, and special language letters like à, ü, etc. Again up to you what to do with this.
I'm trying to create a pattern in PHP that matches 2 or more upper case characters in a string.
I've tried the following, but it only matches 2 or more upper case characters in a row, not the entire string:
preg_match('/[A-Z]{2,}/', $string);
For example, the string "aBcDe" or "Red Apple" should return true.
You just have to allow other characters between your uppercase letters:
^(?:.*?\p{Lu}){2}
Demo
I used \p{Lu} here to include Unicode characters as well. If you don't want that just use [A-Z] instead like you did in your pattern.
This simply means:
^ from the start of the pattern
(?: group:
.*? match anything, but as few chars as possible
\p{Lu} match an uppercase letter
){2} ... two times
If all you need to do is identify that a string contains at least 2 uppercase characters then you can use the following:
[A-Z].*?[A-Z]
Try it here.
If you need to identify the specific uppercase characters in the string then things get more complicated.
UPDATE: As Lucas mentioned, you need a different regex if you want unicode support.
\p{Lu}.*?\p{Lu}
^.*[A-Z].*[A-Z].*$
A simple pattern stating the same would do.See demo.
https://regex101.com/r/pT4tM5/23
[A-Z].*[A-Z]
is about as simple as it gets - match an uppercase followed by anything repeated any number of times followed by any other uppercase letter.
If you need to match the whole line/string that has at least 2 upper case letters, you can also use
^(?=(?:.*[A-Z]){2}).+$
Demo here.
I wanted to use regular expression to check if a string has a word that contains 8 digit of alphanumeric character, ignoring uppercase and lowercase (meaning that 2HJS1289 and 2hjs1289 should match). I know I can use preg to do this, and so far I have this:
preg_match('/[A-Za-z0-9]/i', $string)
I am unsure however on how to limit it only to 8 digits/character scheme.
For exactly 8 char word you will need to use word boundaries: \b
preg_match('/\b[A-Z\d]{8}\b/i', $string)
Try
preg_match('/\b([A-Z0-9]{8})\b/i', $string)
The {8} matches exactly 8 times. I added the capturing group (the parentheses), in case you needed to extract the actual match.
You can also use {min,max} to match the pattern repeating between min and max times (inclusive, I think). Or you can leave one of the parameters out to leave it open ended. Eg {min,} to match at least min times
[a-zA-Z0-9] - will match upper or lowercase letters or numbers
{8} - will specify to match 8 of the preceeding token
put it together:
preg_match('/([A-Za-z0-9]{8})/i', $string)
example