I have the following string:
a simple string that may contain this & that but I want it to skip &&. Do you follow?
I am working with the following regex to try to split it on a double occurrence of "&&":
[^&]*\s
This picks up the single "&" occurrence.
I've also tried:
[^&]{2}*\s
But that doesn't pick up anything.
The stuff I have found online apply to PCRE regex and I am unable to find an RE2 type solution that go uses.
https://regex101.com/r/kgVVvB/1
Normally, you would be able to use (?:(?!&&|(?<=&)&).)+, but since golang doesn't currently support lookaheads or lookbehinds, you have to hack your way around this using regex. Obviously, using string functions may work for your case, but as you mention in the comments below your question this is part of a larger regex, so here it is:
See regex in use here
(?:(?:^|[^&])&(?:[^&]|$)|[^&])+
(?:(?:^|[^&])&(?:[^&]|$)|[^&])+ Match either of the following one or more times
(?:^|[^&])&(?:[^&]|$)
(?:^|[^&]) Assert position at the start of the line or match any character that is not &
& Match this literally
(?:^|[^&]) Assert position at the end of the line or match any character that is not &
[^&] Match any character that is not &
Related
I have the following string:
https://www.google.com/today/sunday/abcde2.hopeho.3345GETD?weatherType=RAOM&...
https://www.google.com/today/monday/jbkwe3.ho4eho.8495GETD?weatherType=WHTDSG&...
I'd like to extract jbkwe3.ho4eho.8495GETD or abcde2.hopeho.3345GETD. Anything between the {weekday}/ and the ?weatherType=.
I've tried (?<=sunday\/)$.*?(?=\?weatherType=) but it only works for the first line and I want to make it applicable to all strings regardless the value of {weekday}.
I tried (?<=\/.*\/)$.*?(?=\?weatherType=) but it didn't work. Could anyone familiar with Regex can lend some help? Thank you!
[Update]
I'm new to regex but I was experimenting it on sublime text editor via the "find" functionality which I think should be PCRE (according to this post)
Try this regex:
(?:sun|mon|tues|wednes|thurs|fri|satur)day\/\K[^?]+(?=\?weatherType)
Click for Demo
Link to Code
Explanation:
(?:sun|mon|tues|wednes|thurs|fri|satur)day - matches the day of a week i.e, sunday,monday,tuesday,wednesday,thursday,friday,saturday
\/ - matches /
\K - unmatches whatever has been matched so far and pretends that the match starts from the current position. This can be used for the PCRE.
[^?]+ - matches 1 or more occurences of any character that is not a ?
(?=\?weatherType) - the above subpattern[^?]+ will match all characters that are not ? until it reaches a position which is immediately followed by a ? followed by weatherType
To make the match case-insensitive, you can prepend the regex with (?i) as shown here
In the examples given, you actually only need to grab the characters between the last forward slash ("/") and the first question mark ("?").
You didn't mention what flavor regex (ie, PCRE, grep, Oracle, etc) you're using, and the actual syntax will vary depending on this, but in general, something like the following (Perl) replacement regex would handle the examples given:
s/.*\/([^?]*)\?.*/$1/gm
There are other (and more efficient) ways, but this will do the job.
Is it possible to negate a word in pure ERE regex (POSIX.2 Extended Regular Expressions) ?
its seems possible to negate a character or class using ^ as [^ab] which will negate either character a b but how to negate a word as ab (and not either)?
If I have a variable with the following value:
week="Monday|Tuesday|Wednesday|Thursday"
Is it possible to extract all content of week without Tuesday to get a result as:
week="Monday|Wednesday|Thursday"
Regards
You cannot negate a word with any regex engine.
It is only possible to match a continuous piece of text in one go. So, you cannot get a Monday|Wednesday|Thursday as full match after running the string through a regex.
If you want to skip a word you usually remove it from the string. Check if your environment offers a replacing feature.
Also, sometimes, it is possible to split a string with the string to skip. Check if there is split support in your environment.
I am having trouble understanding negative regex lookahead / lookbehind. I got the impression from reading tutorials that when you set a criteria to look for, the criteria doesn't form part of the search match.
That seems to hold for positive lookahead examples I tried, but when I tried these negative ones, it matches the entire test string. 1, it shouldn't have matched anything, and 2 even if it did, it wasn't supposed to include the lookahead criteria??
(?<!^And).*\.txt$
with input
And.txt
See: https://regex101.com/r/vW0aXS/1
and
^A.*(?!\.txt$)
with input:
A.txt
See: https://regex101.com/r/70yeED/1
PS: if you're going to ask me which language. I don't know. we've been told to use regex without any specific reference to any specific languages. I tried clicking various options on regex101.com and they all came up the same.
Lookarounds only try to match at their current position.
You are using a lookbehind at the beginning of the string (?<!^And).*\.txt$, and a lookahead at the end of the string ^A.*(?!\.txt$), which won't work. (.* will always consume the whole string as it's first match)
To disallow "And", for example, you can put the lookahead at the beginning of the string with a greedy quantifier .* inside it, so that it scans the whole string:
(?!.*And).*\.txt$
https://regex101.com/r/1vF50O/1
Your understanding is correct and the issue is not with the lookbehind/lookahead. The issue is with .* which matches the entire string in both cases. The period . matches any character and then you follow it with * which makes it match the entire string of any length. Remove it and both you regexes will work:
(?<!^And)\.txt$
^A(?!\.txt$)
Quite a simple one in theory but can't quite get it!
I want a regex in ant which matches anything as long as it has a slash on the end.
Below is what I expect to work
<regexp id="slash.end.pattern" pattern="*/"/>
However this throws back
java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 0
*/
^
I have also tried escaping this to \*, but that matches a literal *.
Any help appreciated!
Your original regex pattern didn't work because * is a special character in regex that is only used to quantify other characters.
The pattern (.)*/$, which you mentioned in your comment, will match any string of characters not containing newlines, however it uses a possibly unnecessary capturing group. .*/$ should work just as well.
If you need to match newline characters, the dot . won't be enough. You could try something like [\s\S]*/$
On that note, it should be mentioned that you might not want to use $ in this pattern. Suppose you have the following string:
abc/def/
Should this be evaluated as two matches, abc/ and def/? Or is it a single match containing the whole thing? Your current approach creates a single match. If instead you would like to search for strings of characters and then stop the match as soon as a / is found, you could use something like this: [\s\S]*?/.
I have a source file with literally hundreds of occurrences of strings flecha.jpg and flecha1.jpg, but I need to find occurrences of any other .jpg image (i.e. casa.jpg, moto.jpg, whatever)
I have tried using a regular expression with negative lookbehind, like this:
(?<!flecha|flecha1).jpg
but it doesn't work! Notepad++ simply says that it is an invalid regular expression.
I have tried the regex elsewhere and it works, here is an example so I guess it is a problem with NPP's handling of regexes or with the syntax of lookbehinds/lookaheads.
So how could I achieve the same regex result in NPP?
If useful, I am using Notepad++ version 6.3 Unicode
As an extra, if you are so kind, what would be the syntax to achieve the same thing but with optional numbers (in this case only '1') as a suffix of my string? (even if it doesn't work in NPP, just to know)...
I tried (?<!flecha[1]?).jpg but it doesn't work. It should work the same as the other regex, see here (RegExr)
Notepad++ seems to not have implemented variable-length look-behinds (this happens with some tools). A workaround is to use more than one fixed-length look-behind:
(?<!flecha)(?<!flecha1)\.jpg
As you can check, the matches are the same. But this works with npp.
Notice I escaped the ., since you are trying to match extensions, what you want is the literal .. The way you had, it was a wildcard - could be any character.
About the extra question, unfortunately, as we can't have variable-length look-behinds, it is not possible to have optional suffixes (numbers) without having multiple look-behinds.
Solving the problem of the variable-length-negative-lookbehind limitation in Notepad++
Given here are several strategies for working around this limitation in Notepad++ (or any regex engine with the same limitation)
Defining the problem
Notepad++ does not support the use of variable-length negative lookbehind assertions, and it would be nice to have some workarounds. Let's consider the example in the original question, but assume we want to avoid occurrences of files named flecha with any number of digits after flecha, and with any characters before flecha. In that case, a regex utilizing a variable-length negative lookbehind would look like (?<!flecha[0-9]*)\.jpg.
Strings we don't want to match in this example
flecha.jpg
flecha1.jpg
flecha00501275696.jpg
aflecha.jpg
img_flecha9.jpg
abcflecha556677.jpg
The Strategies
Inserting Temporary Markers
Begin by performing a find-and-replace on the instances that you want to avoid working with - in our case, instances of flecha[0-9]*\.jpg. Insert a special marker to form a pattern that doesn't appear anywhere else. For this example, we will insert an extra . before .jpg, assuming that ..jpg doesn't appear elsewhere. So we do:
Find: (flecha[0-9]*)(\.jpg)
Replace with: $1.$2
Now you can search your document for all the other .jpg filenames with a simple regex like \w+\.jpg or (?<!\.)\.jpg and do what you want with them. When you're done, do a final find-and-replace operation where you replace all instances of ..jpg with .jpg, to remove the temporary marker.
Using a negative lookahead assertion
A negative lookahead assertion can be used to make sure that you're not matching the undesired file names:
(?<!\S)(?!\S*flecha\d*\.jpg)\S+\.jpg
Breaking it down:
(?<!\S) ensures that your match begins at the start of a file name, and not in the middle, by asserting that your match is not preceded by a non-whitespace character.
(?!\S*flecha\d*\.jpg) ensures that whatever is matched does not contain the pattern we want to avoid
\S+\.jpg is what actually gets matched -- a string of non-whitespace characters followed by .jpg.
Using multiple fixed-length negative lookbehinds
This is a quick (but not-so-elegant) solution for situations where the pattern you don't want to match has a small number of possible lengths.
For example, if we know that flecha is only followed by up to three digits, our regex could be:
(?<!flecha)(?<!flecha[0-9])(?<!flecha[0-9][0-9])(?<!flecha[0-9][0-9][0-9])\.jpg
Are you aware that you're only matching (in the sense of consuming) the extension (.jpg)? I would think you wanted to match the whole filename, no? And that's much easier to do with a lookahead:
\b(?!flecha1?\b)\w+\.jpg
The first \b anchors the match to the beginning of the name (assuming it's really a filename we're looking at). Then (?!flecha1?\b) asserts that the name is not flecha or flecha1. Once that's done, the \w+ goes ahead and consumes the name. Then \.jpg grabs the extension to finish off the match.