FAQ Database Discussion Community


How to describe an optional negative lookahead in regular expression?

regex,grep,lookahead
I like to get the appointment description of calender entries which a program called khal outputs by using grep. The output of khal looks like this: 20:30-22:30 13.05.2015: Manfred treffen Repeat: FREQ=WEEKLY;BYDAY=WE;WKST=MO 09.05. - 12.05.2015: Britt Besuch In the example I would like to match Manfred treffen and Britt Besuch....

Capture a substring of a matched group

regex,lookahead,capturing-group
Scanario I have to grab a substring from a composed string. Match condition: string starts with 'section1:' captured string may be a blank separated or a dash separated list of alphanumerical values if the captured string ends with a specific suffix ('-xx'), exclude the suffix from the captured string. Examples...

Regex for web extraction. Positive lookahead issues

regex,lookahead
Below is an example of some data I'm using. I've read a number of posts involving this topic, as well as tried for a while on regex101. BotInfo[-]: Source IP:[10.1.1.100] Target Host:[CentOS70-1] Target OS:[CentOS 7.0] Description:[HTTP Connection Request] Details:[10.1.1.101 - - [28/May /2013:12:24:08 +0000] "GET /math/html.mli HTTP/1.0" 404 3567 "-"...

Lookahead Behaviour

regex,r,lookahead
How can you make the lookahead non-greedy? I would like the first case not to match anything (like the second case), but it returns "winnie". I guess because it is greedily matching after the "the"? str <- "winnie the pooh bear" ## Unexpected regmatches(str, gregexpr("winnie|bear(?= bear|pooh)", str, perl=T)) # [1]...

Regex that grabs variable number of groups

python,regex,lookahead
This is not a question asking how to use re.findall() or the global modifier (?g) or \g. This is asking how to match n groups with one regex expression, with n between 3 and 5. Rules: needs to ignore lines with first non-space character as # (comments) needs to get...

How can I adjust my positive lookahead RegEx statement?

regex,string,lookahead
I have a really simple question about my positive lookahead, but I don't get it. My String looks like this: caused by: System.StringException: Invalid id: 3285673465734 And I am using this RegEx: caused by: (.+(?=:)): (.+)[\s]+ I want to have this groups: System.StringException Invalid id: 3285673465734 but the positive lookahead...

Match a pattern preceded by a specific pattern without using a lookbehind

regex,eclipse,lookahead
Is there a way to match a B only if preceded by an A? The A can be at any position behind the B, with any amount of characters between. Examples: A_B (Matches `B`) C_B (No match) I've tried: (?=A)[^B]*B But it matches all the characters preceeding B as well....

superfluous LOOKAHEAD in javacc causes error?

java,parsing,javacc,lookahead
I have the following TT.jj, if I uncomment the SomethingElse part below, it successfully parses a language of the form create create blahblah or create blahblah. But if I comment out the SomethingElse part below, but retain the LOOKAHEAD, javacc complains that the lookahead is not necessary and "ignored", but...

Lookahead in regular expression

regex,r,lookahead
I am trying to use a regular expression in order to extract the part of a string before the first " / " occurrence. In the following example the initial string is "Atomic grouping / possessive qualifiers / conditional and recursive patterns" and i want to get "Atomic grouping" library(stringr)...

Regex to create a group from an entire line, or just up to a given token

javascript,regex,lookahead,end-of-line
I'm using a JavaScript Regex Engine. The regex ^(.*?)\s*(?=[*\[]).* will capture a group containing all the characters up to a [ or * character. It works well with these lines, matching the entire line and capturing the first section: This should be captured up to here[ but no further] This...

Parsing text between quotes with .NET regular expressions

c#,.net,regex,lookahead,lookbehind
I have the following input text: @"This is some text @foo=bar @name=""John \""The Anonymous One\"" Doe"" @age=38" I would like to parse the values with the @name=value syntax as name/value pairs. Parsing the previous string should result in the following named captures: name:"foo" value:"bar" name:"name" value:"John \""The Anonymous One\"" Doe"...

grep regex lookahead or start of string (or lookbehind or end of string)

regex,grep,lookahead,lookbehind
I want to match a string which may contain a type of character before the match, or the match may begin at the beginning of the string (same for end of string). For a minimal example, consider the text n.b., which I'd like to match either at the beginning of...

Regex that matches string before comma unless the text contains a clasped list that is also separated by comma

ruby,regex,lookahead
Let's say this is my text: "a, b, c (1, 2, 3), d, f (x, y)" I want to match every point of the enumeration but I also don't want the sub list comma interpreted as a terminating character. I want a regex to extract the following matches: a b...

grepl in R: matching impeded by intra-word dashes

regex,r,lookahead,lookbehind,grepl
I have 3 words: x, y, and z, from which two compound words can be built: x-y, and y-z. In naturally occuring text, x, y, and z can follow each other. In the first case, I have: text="x-y z" And I want to detect: "x-y" but not "y z". If...