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Reference - What does this regex mean?
(1 answer)
Closed 2 years ago.
I am a newbie in regular expression, I have written regular expression for ${serviceName} basicly I want to take the words in between ${ } So I already wrote regular expression for this that is perfectly fine
"\\$\\{(\\w+)\\}"
But what I want to take any values not only the words which are in between ${serviceName.1.Type}.So can you guys help me with regular expression for ${serviceName.1.Type}.
I hope my question is clear.
Thanks In Advance.
A good place to test regular expressions is https://regex101.com/
\w+ matches any word character (equal to [a-zA-Z0-9_])
If you want to match anything you can replace it with: .*
.* matches any character (except for line terminators)
You might want to add a "?" at the end to match to first "}"
*? Quantifier — Matches between zero and unlimited times, as few times as possible, expanding as needed
Also you don't need to escape the { } in this case
So what you want is:
"\\${(.*?)}"
\$\{([\w?\.?\d?\s?]+)\}
This expression captures as a group everything that appears between {}
You can then call the group with the expression $1
On this web you will see your exercise solved and if other expressions have some additional character you can try to add it. Now it is prepared for points \. , spaces \s, letters \w and digits \d
Related
This question already has an answer here:
Regex match numbers not followed by a hyphen
(1 answer)
Closed 1 year ago.
I am trying to capture groups in a text that only match when the match is not followed by a specific character, in this case the opening parentheses "(" to indicate the start of a 'function/method' rather than a 'property'.
This seems pretty straightforward so I tried:
TEXT
$this->willMatch but $this->willNot()
RESULT
RegExp pattern: \$this->[a-zA-Z0-9\_]+(?<!\()
Expected: $this->willMatch
Actual: $this->willMatch, $this->willNot
RegExp pattern: \$this->[a-zA-Z0-9\_]+[^\(]
Expected: $this->willMatch
Actual: $this->willMatch, $this->willNot
RegExp pattern: \$this->[a-zA-Z0-9]+(?!\()
Expected: $this->willMatch
Actual: $this->willMatch, $this->willNo
My intuition says i need to add ^ and $ but that wont work for multiple occurrences in a text.
Curious to meet the RegExp wizard that can solve this!
Answer from The fourth bird definitely works and it is well explained as well.
As an alternative to using word boundary one can use possessive quantifier i.e. ++ to turn off backtracking thus improving efficiency further.
\$this->\w++(?!\()
RegEx Demo
Please note use of \w instead of equivalent [a-zA-Z0-9_] here.
Like a greedy quantifier, a possessive quantifier repeats the token as many times as possible. Unlike a greedy quantifier, it does not give up matches as the engine backtracks.
The (?<!\() will always be true as the character class does not match a (
Note that you don't have to escape the \_
You can use a word boundary after the character class to prevent backtracking, and turn the negative lookbehind into a negative lookahead (?!\() to assert not ( directly to the right.
\$this->[a-zA-Z0-9_]+\b(?!\()
Regex demo
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Regular expressions: Ensuring b doesn't come between a and c
(4 answers)
Closed 4 years ago.
The following regular expression is jumping [url] tags...
Regular Expression (generic regular expression)
(?:\[url.*?\])(.*?youtu.*?)(?:\[\/url\])
String:
[url]blahyoutubeblah[/url] heyya [url]blahblah[/url] [url]www.youtube.com/blah[/url]
Help!!
Your captured group requires youtu inside, so the substring
[url]blahblah[/url] [url]www.youtube.com/blah[/url]
matches, because it starts with [url], includes youtu, and ends with [/url].
Simply using a negated character set, excluding [, probably isn't enough, because that wouldn't allow for nested tags to match, such as an input of
[url]foobar youtube[b]BOLD TEXT[/b][/url]
You might require negative lookahead for [/url] right before each repeated character:
(?:(?!\[\/url\]).)*
Also, make sure that whatever comes after the [url does not contain ]s before coming to the true ], with:
\[url[^]]*\]
In full:
\[url[^]]*\]((?:(?!\[\/url\]).)*youtu(?:(?!\[\/url\]).)*)\[\/url\]
There's no need to make the quantifiers lazy anymore, because of the negative lookahead.
Demo:
https://regex101.com/r/hSAJEp/1
You are matching .* which means it will match url, up until youtu, then find /url
A simple workaround could be something like which means it won't match a opening [ bracket before finding youtu
(?:\[url.*?\])([^\[]*?youtu.*?)(?:\[\/url\])
The problem was that there is youtu you had in your regex but there was blahblah between url to be matched, making it generic
so
(?:\[url.*?\])(.*?)(?:\[\/url\])
It's lazy, but it still will match if it can - it won't be moving left border if match is possible. There are other things to do that. One of them is just to prevent unwanted match by regex itself - just use
(?:\[url[^\]]*?\])([^\[]*?youtu.*?)(?:\[\/url\])
This question already has an answer here:
Reference - What does this regex mean?
(1 answer)
Closed 4 years ago.
the code is presented below
import re
line = "dogs are better than humans"
matchObj = re.match( r'(.*) are (.*?) .*', line)
if matchObj:
print ("matchObj.group() : ", matchObj.group())
(.*): matches and captures any character (except new lines) any number of times. This may be zero times. . denotes "any character" and * signifies repetition. The parentheses are used to denote capture groups (explained below).
are: literal string " are "
(.*?): same as (.*) except it tries to match as few characters as possible (non-greedy). This means that it would try to stop matching as soon as possible. If your string contained multiple spaces after (.*?), this part of the expression would match all those spaces. Adding the non-greedy symbol (?) will make it stop at the first space (since that is the character after this segment of the expression).
.* any character any number of times.
Capture groups or captures for short are portions of the entire match. Wrapping an expression within your regex allows you to easily retrieve that portion of your match.
(dogs) are (better) than humans
(.*) are (.*?) .*
In your example, dogs and better would be captured. These are also referred to as "groups". In regular expressions, they are marked by a pair of parentheses.
Play around with the regex here. Hover on the match to see which portions of the expression are captured.
This question already has answers here:
What do 'lazy' and 'greedy' mean in the context of regular expressions?
(13 answers)
Closed 6 years ago.
Choose which of the following strings match regular expression
(1 U 22)*2*
a. 22112222112211
b. 11112
c. The empty string.
d. 12121
e. 1121111222
I did a few search, U means " Ungreedy. Makes the quantifiers *+?{} consume only those characters absolutely necessary to form a match, leaving the remaining ones available for the next part of the pattern. When the "U" option is not in effect, an individual quantifier can be made non-greedy by following it with a question mark. Conversely, when "U" is in effect, the question mark makes an individual quantifier greedy. " https://www.cheatography.com/davechild/cheat-sheets/regular-expressions/
but I totally don't understand it, what does greedy regular expression and ungreedy regular expression mean? and can you show the example that I listed above?
Greedy means that it will try to find the longest matching string.
For the following string:
{ this} is a { test} }
Example of a Greedy regex
\{.*\}
This regex would match the whole following text:
{ this} is a { test} }
Non Greedy
\{.*\}
would match only
{ this}
This question already has an answer here:
Reference - What does this regex mean?
(1 answer)
Closed 8 years ago.
What is the difference between .* and (.*) in regular expressions?
From what I've seen,
AB.*DE
and
AB(.*)DE
appear to match the same things but I want to know if there are any differences so I use the correct one.
I need to be able to match any number of characters between AB and DE and even match if there isn't anything between them (ABDE).
If .* and (.*) mean the same thing, is there a "better" one to use in terms of standards/best practice?
.* Matches any character zero or more times.
(.*) - Matched characters are stored into a group for later back-referencing(any charcter within () would be captrued).
AB.DE Matches the string ABanycharDE. Dot represent any character except newline character.
AB(.)DE AB and DE are matched and the in-between character is captured.
The parentheses indicate a capture group.
There is no difference. Both will match any character zero+ times. However, the capture group is considered better because it allows you to group together your conditions. This makes your regular expressions look nicer and more readable just like parenthesis in math equations make the equation look nicer.