why this regexp
(?<!\S)[^\s]*[aeiou][^\s]*(?<=\d)(?!\S)
match test123 but not 123test
i want to match a word which must have a vowel and digit .As i am new to this i dont understand all methods completely. maybe thats causing problem.
i want to match a word which must have a vowel and digit
(?<!\S)\S*(?:[aeiou]\S*\d|\d\S*[aeiou])\S*(?!\S)
This part in your regex,
(?<=\d)(?!\S)
will look for a digit to be present which must not be followed by a non-space character. In this test123, because 3 present at the last satisfies this condition where 3 is not followed by a non-space character. So your regex matches test123 and fails to match 123test because all the digits present in this input is followed by a non-space character. And also your regex asserts that there must be an vowel exists before the digit. This is also a reason.
(?<!\S)[^\s]*[aeiou][^\s]*(?<=\d)(?!\S)
^^^^^^^
Because of the lookbehind which makes regex engine look for integer after the last match which is not present in 123test
For your needs you can simply use
\b(?=[a-zA-Z0-9]*[0-9])(?=[a-zA-Z0-9]*[aeiou])[a-zA-Z0-9]+\b
See demo.
https://www.regex101.com/r/fJ6cR4/27
Alternative way of doing this:
def vowel_and_num?(str)
!(str.scan(/[aeiou]/).empty? || str.scan(/[0-9]/).empty?)
end
vowel_and_num?("test123")
# => true
vowel_and_num?("123test")
# => true
vowel_and_num?("test")
# => false
vowel_and_num?("123")
# => false
Related
I'm using Ruby on Rails 5.1. In Ruby, how do I say taht I want to match a string if the first character matches something but the sequence that follows does NOT match a pattern? That is, I want to match a number provided that the sequence taht follows is not a character from an array I have followed by two other numbers. Here's my character array ...
2.4.0 :010 > TOKENS
=> [":", ".", "'"]
So this string would NOT match
3:00
since ":00" matches the pattern of a character from my array followed by two numbers. But this string
3400
would match. This string would also match
3:0
and this would match
3
since nothing follows the above. How do I write the appropriate regex in Ruby?
string =~ /\A\d+(?!:\d{2})/
This regular expression means:
\A anchors the match to the start of the string.
\d+ means "one or more digits".
(?!...) is a negative look-ahead. It checks that the pattern contained in the brackets does not match., looking ahead from the current position.
:\d{2} means : followed by two digits.
Consideration should be given to testing the first character and the remaining characters separately.
def match_it?(str, first_char_regex, no_match_regex)
str[0].match?(first_char_regex) && !str[1..-1].match?(no_match_regex)
end
match_it?("0:00", /0/, /\A[:. ]cat\z/) #=> true
match_it?("0:00", /\d/, /\A[:. ]\d+\z/) #=> false
match_it?("0:00", /[[:alpha:]]/, /\A[:. ]\d+\z/) #=> false
I believe this reads well and it simplifies testing when compared to methods that employ a single regular expression.
I am writing some code that needs to convert a string to camel case. However, I want to allow any _ or - at the beginning of the code.
I have had success matching up an _ character using the regex here:
^(?!_)(\w+)_(\w+)(?<!_)$
when the inputs are:
pro_gamer #matched
#ignored
_proto
proto_
__proto
proto__
__proto__
#matched as nerd_godess_of, skyrim
nerd_godess_of_skyrim
I recursively apply my method on the first match if it looks like nerd_godess_of.
I am having troubled adding - matches to the same, I assumed that just adding a - to the mix like this would work:
^(?![_-])(\w+)[_-](\w+)(?<![_-])$
and it matches like this:
super-mario #matched
eslint-path #matched
eslint-global-path #NOT MATCHED.
I would like to understand why the regex fails to match the last case given that it worked correctly for the _.
The (almost) full set of test inputs can be found here
The fact that
^(?![_-])(\w+)[_-](\w+)(?<![_-])$
does not match the second hyphen in "eslint-global-path" is because of the anchor ^ which limits the match to be on the first hyphen only. This regex reads, "Match the beginning of the line, not followed by a hyphen or underscore, then match one or more words characters (including underscores), a hyphen or underscore, and then one or more word characters in a capture group. Lastly, do not match a hyphen or underscore at the end of the line."
The fact that an underscore (but not a hyphen) is a word (\w) character completely messes up the regex. In general, rather than using \w, you might want to use \p{Alpha} or \p{Alnum} (or POSIX [[:alpha:]] or [[:alnum:]]).
Try this.
r = /
(?<= # begin a positive lookbehind
[^_-] # match a character other than an underscore or hyphen
) # end positive lookbehind
( # begin capture group 1
(?: # begin a non-capture group
-+ # match one or more hyphens
| # or
_+ # match one or more underscores
) # end non-capture group
[^_-] # match any character other than an underscore or hyphen
) # end capture group 1
/x # free-spacing regex definition mode
'_cats_have--nine_lives--'.gsub(r) { |s| s[-1].upcase }
#=> "_catsHaveNineLives--"
This regex is conventionally written as follows.
r = /(?<=[^_-])((?:-+|_+)[^_-])/
If all the letters are lower case one could alternatively write
'_cats_have--nine_lives--'.split(/(?<=[^_-])(?:_+|-+)(?=[^_-])/).
map(&:capitalize).join
#=> "_catsHaveNineLives--"
where
'_cats_have--nine_lives--'.split(/(?<=[^_-])(?:_+|-+)(?=[^_-])/)
#=> ["_cats", "have", "nine", "lives--"]
(?=[^_-]) is a positive lookahead that requires the characters on which the split is made to be followed by a character other than an underscore or hyphen
you can try the regex
^(?=[^-_])(\w+[-_]\w*)+(?=[^-_])\w$
see the demo here.
Switch _- to -_ so that - is not treated as a range op, as in a-z.
I am searching for strings with only letters or numbers or both. How could I write a regex for that?
You can use following regex to check if the string contains letters and/or numbers
^[a-zA-Z0-9]+$
Explanation
^: Starts with
[]: Character class
a-zA-Z: Matches any alphabet
0-9: Matches any number
+: Matches previous characters one or more time
$: Ends with
RegEx101 Demo
"abc&#*(2743438" !~ /[^a-z0-9]/i # => false
"abc2743438" !~ /[^a-z0-9]/i # => true
This example let to avoid multiline anchors use (^ or $) (which may present a security risk) so it's better to use \A and \z, or to add the :multiline => true option in Rails.
Only letters and numbers:
/\A[a-zA-Z0-9]+\z/
Or if you want to leave - and _ chars also:
/\A[a-zA-Z0-9_\-]+\z/
I'm doing a regex to check a slug.
Actually my regex is : /^[^-][a-z\-].*[^-]+$/
here's what I'm checking right now :
my-awesome-project => valid
-my-awesome-project => invalid
my-awesome-project- => invalid
Now what I want is to check if the dash is repeating or not :
my-awesome-project => should be valid
my-awesome--project => should not be valid
my----awesome-project => should not be valid
Can I do that with a regex ?
Thank you,
I think this regexp should work:
/^[a-z]+(-[a-z]+)*$/
What this does: ^[a-z]+ matches if the string begins with at least on character. After that there may be (-[a-z]+)*$ zero or more occurances of a dash followed by again at least one character.
See on Rubular.
As I understand, the string is valid unless it:
contains a character other than a lower-case letter or hyphen,
begins with a hyphen,
ends with a hyphen, or
contains two (or more) hyphens in a row.
If that's the case, it's easiest to check if it invalid:
R = /
[^a-z-] # match one character other than a lower-case letter or hyphen
| # or
^- # match a hyphen as the first character
| # or
-$ # match a hyphen as the last character
| # or
-- # match two hypens
/x
def valid?(str)
str !~ R
end
valid? 'my-awesome-project' #=> true
valid? '-my-awesome-project' #=> false
valid? 'my-awesome-project-' #=> false
valid? 'my-awesome--project' #=> false
valid? 'my----awesome-project' #=> false
Below regex may be helpful.
[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*
How would I write a regexp so that the string MUST equal the exact format in the regexp?
For example:
/\d:\d/ =~ 5:4
BUT
/\d:\d/ is also equal to 5:42alskjf2425
how do I make it so that my regexp checks for only a digit, followed by a colon, followed by a digit, and nothing else?
Thanks.
Use \A and \z anchors, to match the beginning and end of a string:
/\A\d:\d\z/ =~ '5:4' # => 0 (boolean true)
/\A\d:\d\z/ =~ '5:4x' # => nil (boolean false)
If you need to specify how many characters must be found, you can do it a couple ways:
\d finds one.
\d{1} finds one.
\d{1,2} finds one or two.
\d{1,} finds one or more.
\d{,2} finds zero, one or two.
In other words, use:
/\d{1}:\d{1}/
Check it out:
'5:4'[/\d{1}:\d{1}/] # => "5:4"
'5:42alskjf2425'[/\d{1}:\d{1}/] # => "5:4"
That's all documented so take the time to read through the Regexp documentation.