I am trying to create a regex that will match the first 3 characters of a string,
If I have a string ABCFFFF I want to verify that the first 3 characters are ABC.
It's pretty straightforward, the pattern would be ^ABC
As others may point out, using regular expressions for such a task is an overkill. Any programming language with regex support can do it better with simple string manipulations.
Just simple regex will work:
/^ABC/
But is it a good use case for using regex, I am not sure. Consider using substring in whatever language/platform you're using.
"^ABC" should work. '^' matches the start in most regex implementations.
Related
I'm trying to use a regular expression to match on a string. Brackets are special characters within regex, am I'm unsure of how'd i'd go about including them in my regex.
To provide more context, I want to find a string such as test[test]
My regex currently looks like this: ^*test[test]. My expression is built out more much than this, but this example is enough to understand the problem.
How can i search for brackets in my string without triggering a character class. I need to use a regex, please don't recommend switching to something else.
You can escape a character with a backslash so \[
I can highly recommend https://regex101.com/ to test your regex without having to code it.
Try: ^.*test\[test\] - This mean {start of line}, {anything}, "test[test]".
I'm trying for a few hours to write a pattern for some matching algorithm and I can't manage to find something for the following issue: given the example "my_name_is", I need to extract all words individually, as well as the whole expression. Consider that it may be a list of n examples, some that can be matched, some that cannot be matched.
"my_name_is" => ["my", "name", "is", "my_name_is"]
How can I do this, how should the regexp look like? Looking forward for your answers, thank you!
Regular Expressions are patterns used to match a string of characters. We usually use them to validate a string of characters, or to find and replace a specific pattern within text.
Here, it seems the outcome you're looking for is an array of strings that have been split using an underscore. Regex isn't what you're looking for.
Implementation would change based on language, but consider the following code:
function stringToArray(myStr)
{
words = str_split(myStr, '_');
return array_merge(words, [myStr]);
}
use re.findall with the following as your regex:
([^_]+)+?
This should match all sets of consecutive characters that don't contain the underscore.
As for the whole thing? You already have it, so there's no reason to regex the whole string
I have a string with multiline as below.
rawMessage=sysUpTimeInstance-->0:0:00:05.00
snmpTrapOID.0-->linkDown.0.0
In the drools when portion i have written the condition as below.
rawMessage matches "(?i).*linkDown(.|\n|\r)*"
but it is not working.Please provide me some pointers to handle multiline.
Its not clear to me what you want to do/achieve. Your regex looks not wrong (I don't know the drools flavour and what you want to match).
In general (.|\n|\r)* is able to match any character including newlines. In your example there is no newline after "linkDown", so what should it match there?
Maybe you need to double escape (I don't know for drools) like this: (.|\\n|\\r)*.
Another possibility is to use the singleline modifer s (Again, I don't know if drools supports this modifier). This makes the . match also newline characters, could then look something like this
rawMessage matches "(?i)(?s).*linkDown.*"
or if it should only match multiline from "linkdown" on
rawMessage matches "(?i).*linkDown(?s).*"
Drools uses standard java regular expressions. As the previous answer mention, your expression looks wrong. And yes, you need to double escape special chars like you would do in java. Just check the javadoc for the Pattern class in the java API.
I got a string like this:
PREFIX-('STRING WITH SPACES TO REPLACE')
and i need this:
PREFIX-('STRING_WITH_SPACES_TO_REPLACE')
I'm using Notepad++ for the Regex Search and Replace, but i'm shure every other Editor capable of regex replacements can do it to.
I'm using:
PREFIX-\('(.*)(\s)(.*)'\)
for search and
PREFIX-('\1_\3')
for replace
but that replaces only one space from the string.
The regex search feature in Notepad++ is very, very weak. The only way I can see to do this in NPP is to manually select the part of the text you want to work on, then do a standard find/replace with the In selection box checked.
Alternatively, you can run the document through an external script, or you can get a better editor. EditPad Pro has the best regex support I've ever seen in an editor. It's not free, but it's worth paying for. In EPP all I had to do was this:
search: ((?:PREFIX-\('|\G)[^\s']+)\s+
replace: $1_
EDIT: \G matches the position where the previous match ended, or the beginning of the input if there was no previous match. In other words, the first time you apply the regex, \G acts like \A. You can prevent that by adding a negative lookahead, like so:
((?:PREFIX-\('|(?!\A)\G)[^\s']+)\s+
If you want to prevent a match at the very beginning of the text no matter what it starts with, you can move the lookahead outside the group:
(?!\A)((?:PREFIX-\('|\G)[^\s']+)\s+
And, just in case you were wondering, a lookbehind will work just as well as a lookahead:
((?:PREFIX-\('|(?<!\A)\G)[^\s']+)\s+
You have to keep matching from the beggining of the string untill you can match no more.
find /(PREFIX-\('[^\s']*)\s([^']*'\))/
replace $1_$2
like: while (/(PREFIX-\('[^\s']*)\s([^']*'\))/$1_$2/) {}
How about using Replace all for about 20 times? Or until you're sure no string contains more spaces
Due to nature of regex, it's not possible to do this in one step by normal regular expression.
But if I be in your place, I do such replaces in several steps:
find such patterns and mark them with special character
(Like replacing STRING WITH SPACES TO REPLACE with #STRING WITH SPACES TO REPLACE#
Replace #([^#\s]*)\s to #\1_ server times.
Remove markers!
I studied a little the regex tool in Notepad++ because I didn't know their possibilities.
I conclude that they aren't powerful enough to do what you want.
Your are obliged to learn and use a programming language having a real regex capability. There are a number of them. Personnaly, I use Python. It would take 1 mn to do what you want with it
You'd have to run the replace several times for each space but this regex will work
/(?<=PREFIX-\(')([^\s]+)\s+/g
Replace with
\1_ or $1_
See it working at http://refiddle.com/10z
I have a regex pattern to match an HTML script tag. How can I change this script tag pattern so that the patterns means "input string DOES NOT MATCH" the script tag pattern?
In other words, given a pattern, what is the alteration needed to change the meaning of the pattern to "does not match this pattern"?
For example, if I have a pattern: \d{3}-\d{3}-\d{4}, what is the equivalent pattern for this that means "does not match \d{3}-\d{3}-\d{4}"?
You can negate a regex pattern by using a negative lookahead. This is slightly different than simply negating the regex though. Negative lookahead would look like the following in Java (and many other languages):
(?!\d{3}-\d{3}-\d{4})
It should be noted that this doesn't exactly answer the question. Finding the inverse of a regular language is not an easy task using a regular expression (I don't think). A much easier way to solve the problem would be to inverse the program logic:
Instead of:
if (string.matches(yourRegex))
Do:
if (!string.matches(yourRegex))
That is not easily achievable for arbitrary patterns. In practice, it's almost always easier to do what you want in the surrounding code than in the pattern itself. For instance, instead of
grep '\d{3}-\d{3}-\d{4}' file
you could use
grep -v '\d{3}-\d{3}-\d{4|' file
Or in a program you could change something like
if (pattern.matches()) {
foo();
}
into something like
if (!pattern.matches()) {
foo();
}
In a more tedious approach, you would have to enumerate all possible values that should match instead of what should not match. So, say you want to match everything but the string <html>, you could write a regex like so:
([^<]|<([^h]|h([^t]|t([^m]|m([^l]|l[^>])))))
Reading that regex is like saying: "Okay, you can match any character but '<', or you could match '<' but then you can't match an 'h' after that... or you do match an 'h' after that but then you can't match a 't' after that... and so on.
It's butt ugly, but then again, for simple string matches, you can easily write a recursive function that transforms any given term into a pattern like the above.
easier to just negate the test surely? eg...
if (!regex.test(str)) ...
(javascript example)
Negating a character class is easy with ^ but a whole regex will get much more convoluted.
What language are you using? The easiest solution to the specific problem you stated is to simply prepend a negation operator (usually "!") to the match.
I definitely agree with the other answers saying you should negate testing for a match, but this should do what you want using just a regex:
(?!.*\d{3}-\d{3}-\d{4})
This is a negative lookahead, by not placing any characters outside of the lookahead the regex basically means "fail on any string that starts with any number of characters (.*) followed by the regex \d{3}-\d{3}-\d{4}".