Hello I need coming up with a valid regular expression It could be any identifier name that starts with a letter or underscore but may contain any number of letters, underscores, and/or digits (all letters may be upper or lower case).
For example, your regular expression should match the following text strings: “_”, “x2”, and “This_is_valid” It should not match these text strings: “2days”, or “invalid_variable%”.
So far this is what I have came up with but I don't think it is right
/^[_\w][^\W]+/
The following will work:
/^[_a-zA-Z]\w*$/
Starts with (^) a letter (upper or lowercase) or underscore ([_a-zA-Z]), followed by any amount of letter, digit, or underscore (\w) to the end ($)
Read more about Regular Expressions in Perl
Maybe the below regex:
^[a-zA-Z_]\w*$
If the identify is at the start of a string, then it's easy
/^(_|[a-zA-Z]).*/
If it's embedded in a longer string, I guess it's not much worse, assuming it's the start of a word...
/\s(_|[a-zA-Z]).*/
Related
I understand the meaning of [A-Za-z0-9_]+ corresponding to a repeated sequence of one or more characters containing upper case letters, lower case letters, digits and underscores, but what does the whole expression corresponds to?
I'm going to assume that your regex is /[A-Za-z0-9_]+(?=\s+)/ and that your programming language requires you to escape the \ as \\.
Like you said, [A-Za-z0-9_]+ matches one or more alpha-numeric characters.
The (?=) pattern indicates a positive look ahead expression. We are checking if after the alpha-numeric characters, we have one or more(+) whitespace(\s) characters. However, the difference between /[A-Za-z0-9_]+\s+/ and /[A-Za-z0-9_]+(?=\s+)/ is that the former would include the whitespace in the match while the latter will not.
If you run your regex on this_is_followed_by_whitespace␠␠␠ where "␠" indicates spaces, only this_is_followed_by_whitespace will be matched. The expression is just looking ahead to check whether there is whitespace. Running /[A-Za-z0-9_]+\s+/ on the same string would match this_is_followed_by_whitespace␠␠␠.
Play around with your regex on this RegExr demo.
I hate regex and I really can't get my head around it properly. I'm trying to match the following example:
fwb fcb"><a href="https://www.facebook.com/random.length?
while random.length can be any word with upper/lowercase letters, a dot or a number. And it ends with the ? so the question mark indicates the end.
I came as far as:
/fwb fcb"><a href="https:\/\/www.facebook.com\/ missing bit ?/g
Any help?
[a-zA-Z0-9\.]+\? should do the trick.
a-z matches all lowercase letters.
A-Z matches all uppercase letters.
0-9 matches all digits.
You need to escape the dot with a backslash as it has a special meaning in regex.
+ means that the length of the string can be anything from 1 to infinity.
the missing part could be (\w|\.)+ if underscore was accepted. Otherwise, like in your case, you have to specify all different possibilities: [A-Za-z0-9\.]+. Pay attention because in your regex there are some characters that need to be escaped (. and ? are an example).
I am new to the regular expression and trying to build a expression wherein i want to check if the first three letters of the string are in upper case ?
I have expression like this "ALB.latin" or CAT.Cyrillic etc . i just want to check if the first three letters before the dot/period are capital and letter after the dot/period are in title case.
I have tried to build expression like to in FME test filter ^[A-Z]{3}\.[A-Za-z]$.
You need to remove the $ anchor from the pattern as it requires the end of string to appear right after the last [A-Za-z] subpattern matches an uppercase letter.
If you just need to check if the string starts with 3 uppercase ASCII letters, . and an ASCII letter, use
^[A-Z]{3}\.[A-Za-z]
Or, if you also need to make sure there are 1 or more ASCII letters only at the end, add + between [A-Za-z] and $, to match 1 or more symbols defined in the [a-zA-Z] character class:
^[A-Z]{3}\.[A-Za-z]+$
See the regex demo.
Hope this will give you the solution.
^[A-Z]{3}\.[A-Z][a-z]*$
With this, Letter after DOT will be in Title case. But at least one title case letter should be there after DOT.
I am having problems creating a regex validator that checks to make sure the input has uppercase or lowercase alphabetical characters, spaces, periods, underscores, and dashes only. Couldn't find this example online via searches. For example:
These are ok:
Dr. Marshall
sam smith
.george con-stanza .great
peter.
josh_stinson
smith _.gorne
Anything containing other characters is not okay. That is numbers, or any other symbols.
The regex you're looking for is ^[A-Za-z.\s_-]+$
^ asserts that the regular expression must match at the beginning of the subject
[] is a character class - any character that matches inside this expression is allowed
A-Z allows a range of uppercase characters
a-z allows a range of lowercase characters
. matches a period
rather than a range of characters
\s matches whitespace (spaces and tabs)
_ matches an underscore
- matches a dash (hyphen); we have it as the last character in the character class so it doesn't get interpreted as being part of a character range. We could also escape it (\-) instead and put it anywhere in the character class, but that's less clear
+ asserts that the preceding expression (in our case, the character class) must match one or more times
$ Finally, this asserts that we're now at the end of the subject
When you're testing regular expressions, you'll likely find a tool like regexpal helpful. This allows you to see your regular expression match (or fail to match) your sample data in real time as you write it.
Check out the basics of regular expressions in a tutorial. All it requires is two anchors and a repeated character class:
^[a-zA-Z ._-]*$
If you use the case-insensitive modifier, you can shorten this to
^[a-z ._-]*$
Note that the space is significant (it is just a character like any other).
In my ASP.NET page, I have an input box that has to have the following validation on it:
Must be alphanumeric, with at least one letter (i.e. can't be ALL
numbers).
^\d*[a-zA-Z][a-zA-Z0-9]*$
Basically this means:
Zero or more ASCII digits;
One alphabetic ASCII character;
Zero or more alphanumeric ASCII characters.
Try a few tests and you'll see this'll pass any alphanumeric ASCII string where at least one non-numeric ASCII character is required.
The key to this is the \d* at the front. Without it the regex gets much more awkward to do.
Most answers to this question are correct, but there's an alternative, that (in some cases) offers more flexibility if you want to change the rules later on:
^(?=.*[a-zA-Z].*)([a-zA-Z0-9]+)$
This will match any sequence of alphanumerical characters, but only if the first group also matches the whole sequence. It's a little-known trick in regular expressions that allows you to handle some very difficult validation problems.
For example, say you need to add another constraint: the string should be between 6 and 12 characters long. The obvious solutions posted here wouldn't work, but using the look-ahead trick, the regex simply becomes:
^(?=.*[a-zA-Z].*)([a-zA-Z0-9]{6,12})$
^[\p{L}\p{N}]*\p{L}[\p{L}\p{N}]*$
Explanation:
[\p{L}\p{N}]* matches zero or more Unicode letters or numbers
\p{L} matches one letter
[\p{L}\p{N}]* matches zero or more Unicode letters or numbers
^ and $ anchor the string, ensuring the regex matches the entire string. You may be able to omit these, depending on which regex matching function you call.
Result: you can have any alphanumeric string except there's got to be a letter in there somewhere.
\p{L} is similar to [A-Za-z] except it will include all letters from all alphabets, with or without accents and diacritical marks. It is much more inclusive, using a larger set of Unicode characters. If you don't want that flexibility substitute [A-Za-z]. A similar remark applies to \p{N} which could be replaced by [0-9] if you want to keep it simple. See the MSDN page on character classes for more information.
The less fancy non-Unicode version would be
^[A-Za-z0-9]*[A-Za-z][A-Za-z0-9]*$
^[0-9]*[A-Za-z][0-9A-Za-z]*$
is the regex that will do what you're after. The ^ and $ match the start and end of the word to prevent other characters. You could replace the [0-9A-z] block with \w, but i prefer to more verbose form because it's easier to extend with other characters if you want.
Add a regular expression validator to your asp.net page as per the tutorial on MSDN: http://msdn.microsoft.com/en-us/library/ms998267.aspx.
^\w*[\p{L}]\w*$
This one's not that hard. The regular expression reads: match a line starting with any number of word characters (letters, numbers, punctuation (which you might not want)), that contains one letter character (that's the [\p{L}] part in the middle), followed by any number of word characters again.
If you want to exclude punctuation, you'll need a heftier expression:
^[\p{L}\p{N}]*[\p{L}][\p{L}\p{N}]*$
And if you don't care about Unicode you can use a boring expression:
^[A-Za-z0-9]*[A-Za-z][A-Za-z0-9]*$
^[0-9]*[a-zA-Z][a-zA-Z0-9]*$
Can be
any number ended with a character,
or an alphanumeric expression started with a character
or an alphanumeric expression started with a number, followed by a character and ended with an alphanumeric subexpression