Here's my regular expression that I have for this. I'm in Ruby, which — if I'm not mistaken — uses POSIX regular expressions.
regex = /(?:\n^)(\*[\w+ ?]+\*)\n/
Here's my goal: I want to split a string with a regex that is *delimited by asterisks*, including those asterisks. However: I only want to split by the match if it is prefaced with a newline character (\n), or it's the start of the whole string. This is the string I'm working with.
"*Friday*\nDo not *break here*\n*But break here*\nBut again, not this"
My regular expression is not splitting properly at the *Friday* match, but it is splitting at the *But break here* match (it's also throwing in a here split). My issue is somewhere in the first group, I think: (?:\n^) — I know it's wrong, and I'm not entirely sure of the correct way to write it. Can someone shed some light? Here's my complete code.
regex = /(?:\n^)(\*[\w+ ?]+\*)\n/
str = "*Friday*\nDo not *break here*\n*But break here*\nBut again, not this"
str.split(regex)
Which results in this:
>>> ["*Friday*\nDo not *break here*", "*But break here*", "But again, not this"]
I want it to be this:
>>> ["*Friday*", "Do not *break here*", "*But break here*", "But again, not this"]
Edit #1: I've updated my regex and result. (2011/10/18 16:26 CST)
Edit #2: I've updated both again. (16:32 CST)
What if you just add a '\n' to the front of each string. That simplifies the processing quite a bit:
regex = /(?:\n)(\*[\w+ ?]+\*)\n/
str = "*Friday*\nDo not *break here*\n*But break here*\nBut again, not this"
res = ("\n"+str).split(regex)
res.shift if res[0] == ""
res
=> [ "*Friday*", "Do not *break here*",
"*But break here*", "But again, not this"]
We have to watch for the initial extra match but it's not too bad. I suspect someone can shorten this a bit.
Groups 1 & 2 of the regex below :
(?:\A|\\n)(\*.*?\*)|(?:\A|\\n)(.*?)(?=\\n|\Z)
Will give you your desired output. I am no ruby expert so you will have to create the list yourself :)
Why not just split at newlines? From your example, it looks that's what you're really trying to do.
str.split("\n")
Related
Lets say I have the following string and I want the below output without requiring csv.
this, "what I need", to, do, "i, want, this", to, work
this
what i need
to
do
i, want, this
to
work
This problem is a classic case of the technique explained in this question to "regex-match a pattern, excluding..."
We can solve it with a beautifully-simple regex:
"([^"]+)"|[^, ]+
The left side of the alternation | matches complete "quotes" and captures the contents to Group1. The right side matches characters that are neither commas nor spaces, and we know they are the right ones because they were not matched by the expression on the left.
Option 2: Allowing Multiple Words
In your input, all tokens are single words, but if you also want the regex to work for my cat scratches, "what I need", your dog barks, use this:
"([^"]+)"|[^, ]+(?:[ ]*[^, ]+)*
The only difference is the addition of (?:[ ]*[^, ]+)* which optionally adds spaces + characters, zero or more times.
This program shows how to use the regex (see the results at the bottom of the online demo):
subject = 'this, "what I need", to, do, "i, want, this", to, work'
regex = /"([^"]+)"|[^, ]+/
# put Group 1 captures in an array
mymatches = []
subject.scan(regex) {|m|
$1.nil? ? mymatches << $& : mymatches << $1
}
mymatches.each { |x| puts x }
Output
this
what I need
to
do
i, want, this
to
work
Reference
How to match (or replace) a pattern except in situations s1, s2, s3...
Article about matching a pattern unless...
I was doing the challenges from pythonchallenge writing code in ruby, specifically this one. It contains a really long string in page source with special characters. I was trying to find a way to delete them/check for the alphabetical chars.
I tried using scan method, but I think I might not use it properly. I also tried delete! like that:
a = "PAGE SOURCE CODE PASTED HERE"
a.delete! "!", "#" #and so on with special chars, does not work(?)
a
How can I do that?
Thanks
You can do this
a.gsub!(/[^0-9A-Za-z]/, '')
try with gsub
a.gsub!(/[!#%&"]/,'')
try the regexp on rubular.com
if you want something more general you can have a string with valid chars and remove what's not in there:
a.gsub!(/[^abcdefghijklmnopqrstuvwxyz ]/,'')
When you give multiple arguments to string#delete, it's the intersection of those arguments that is deleted. a.delete! "!", "#" deletes the intersections of the sets ! and # which means that nothing will be deleted and the method returns nil.
What you wanted to do is a.delete! "!#" with the characters to delete passed as a single string.
Since the challenge is asking to clean up the mess and find a message in it, I would go with a whitelist instead of deleting special characters. The delete method accepts ranges with - and negations with ^ (similar to a regex) so you can do something like this: a.delete! "^A-Za-z ".
You could also use regular expressions as shown by #arieljuod.
gsub is one of the most used Ruby methods in the wild.
specialname="Hello!#$#"
cleanedname = specialname.gsub(/[^a-zA-Z0-9\-]/,"")
I think a.gsub(/[^A-Za-z0-9 ]/, '') works better in this case. Otherwise, if you have a sentence, which typically should start with a capital letter, you will lose your capital letter. You would also lose any 1337 speak, or other possible crypts within the text.
Case in point:
phrase = "Joe can't tell between 'large' and large."
=> "Joe can't tell between 'large' and large."
phrase.gsub(/[^a-z ]/, '')
=> "oe cant tell between large and large"
phrase.gsub(/[^A-Za-z0-9 ]/, '')
=> "Joe cant tell between large and large"
phrase2 = "W3 a11 f10a7 d0wn h3r3!"
phrase2.gsub(/[^a-z ]/, '')
=> " a fa dwn hr"
phrase2.gsub(/[^A-Za-z0-9 ]/, '')
=> "W3 a11 f10a7 d0wn h3r3"
If you don't want to change the original string - i.e. to solve the challenge.
str.each_char do |letter|
if letter =~ /[a-z]/
p letter
end
end
You will have to write down your own string sanitize function, could easily use regex and the gsub method.
Atomic sample:
your_text.gsub!(/[!#\[;\]^%*\(\);\-_\/&\\|$\{#\}<>:`~"]/,'')
API sample:
Route: post 'api/sanitize_text', to: 'api#sanitize_text'
Controller:
def sanitize_text
return render_bad_request unless params[:text].present? && params[:text].present?
sanitized_text = params[:text].gsub!(/[!#\[;\]^%*\(\);\-_\/&\\|$\{#\}<>:`~"]/,'')
render_response( {safe_text: sanitized_text})
end
Then you call it
POST /api/sanitize_text?text=abcdefghijklmnopqrstuvwxyz123456<>$!#%23^%26*[]:;{}()`,.~'"\|/
I have the following string:
nothing to match
<-
this rocks should match as should this still and this rocks and still
->
should not match still or rocks
<- no matches here ->
And i want to find all matches of 'rocks' and 'still', but only when they are within <- ->
The purpose is to markup glossary words but be able to only mark them up in areas of text that are defined by the editor.
I currently have:
<-.*?(rocks|still).*?->
This unfortunately only matches the first 'rocks' and ignores all subsequent instances and all the 'still's
I have this in a Rubular
The usage of this will be somthing like
Regexp.new( '<-.*?(' + self.all.map{ |gt| gt.name }.join("|") + ').*?->', Regexp::IGNORECASE, Regexp::MULTILINE )
Thanks in advance for any help
There may be a way to do this with a single regex, but it will probably be simpler to just do it in two steps. First match all of the markups, and then search the markups for the glossary words:
text = <<END
nothing to match
<-
this rocks should match as should this still and this rocks and still
->
should not match still or rocks
<- no matches here ->
END
text.scan(/<-.*?->/m).each do |match|
print match.scan(/rocks|still/), "\n"
end
Also, you should probably note that regex is only a good solution here if there is never any nested markup (<-...<-...->...->) and no escaped <- or -> whether it is inside or outside of a markup.
Don't forget your Ruby string methods. Use them first before considering regular expressions
$ ruby -0777 -ne '$_.split("->").each{|x| x.split("<-").each{|y| puts "#{y}" if (y[/rocks.*still/]) } }' file
In Ruby, it depends on what you want to do with the regexp. You're matching a regular expression against a string, so you'll be using String methods. Certain of these will have an effect on all matches (e.g. gsub or rpartition); others will have an effect on only the first match (e.g. rindex, =~).
If you're working with any of the latter (that return only the first match), you'll want to make use of a loop that calls the method again, starting from a certain offset. For example:
# A method to print the indices of all matches
def print_match_indices(string, regex)
i = string.rindex(regex, 0)
while !i.nil? do
puts i
i = string.rindex(regex, i+1)
end
end
(Yes, you can use split first, but I expect that a regex loop like the foregoing would require fewer system resources.)
I have a string in Ruby:
str = "<TAG1>Text 1<TAG1>Text 2"
I want to use gsub to get a string like this:
want = "<TAG2>Text 1</TAG2><TAG2>Text2</TAG2>"
In other words, I want to save everything in between a <TAG1> and EITHER: 1) the next occurrence of a "<", or 2) the end of the string.
The best regex i could come up with was:
regex = /<TAG1>(.*)(?:<|$)/
But the problem with this is that it'll just match the entire str, where what I want is both matches within str. (In other words, it seems like the end of string char ($) seems to have precedence over the "<" character--is there a way to flip it around?
/<TAG1>([^<]*)/ will match that. If there's no < it'll go all the way to the end of the string. Otherwise it will stop when it hits a <. Your problem is that . matches < as well. An alternative way would be to do /<TAG1>(.*?)(?:<|$)/, which makes the * non-greedy.
Ruby 1.9.1, OSX 10.5.8
I'm trying to write a simple app that parses through of bunch of java based html template files to replace a period (.) with an underscore if it's contained within a specific tag. I use ruby all the time for these types of utility apps, and thought it would be no problem to whip up something using ruby's regex support. So, I create a Regexp.new... object, open a file, read it in line by line, then match each line against the pattern, if I get a match, I create a new string using replaceString = currentMatch.gsub(/./, '_'), then create another replacement as whole string by newReplaceRegex = Regexp.escape(currentMatch) and finally replace back into the current line with line.gsub(newReplaceRegex, replaceString) Code below, of course, but first...
The problem I'm having is that when accessing the indexes within the returned MatchData object, I'm getting the first result twice, and it's missing the second sub string it should otherwise be finding. More strange, is that when testing this same pattern and same test text using rubular.com, it works as expected. See results here
My pattern:
(<(?:WEBOBJECT|webobject) (?:NAME|name)=(?:[a-zA-Z0-9]+.)+(?:[a-zA-Z0-9]+)(?:>))
Text text:
<WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>moreNonMatchingText<WEBOBJECT NAME=admin.SecondLineMatch>AndEvenMoreNonMatchingText
Here's the relevant code:
tagRegex = Regexp.new('(<(?:WEBOBJECT|webobject) (?:NAME|name)=(?:[a-zA-Z0-9]+\.)+(?:[a-zA-Z0-9]+)(?:>))+')
testFile = File.open('RegexTestingCompFix.txt', "r+")
lineCount=0
testFile.each{|htmlLine|
lineCount += 1
puts ("Current line: #{htmlLine} at line num: #{lineCount}")
tagMatch = tagRegex.match(htmlLine)
if(tagMatch)
matchesArray = tagMatch.to_a
firstMatch = matchesArray[0]
secondMatch = matchesArray[1]
puts "First match: #{firstMatch} and second match #{secondMatch}"
tagMatch.captures.each {|lineMatchCapture|
puts "Current capture for tagMatches: #{lineMatchCapture} of total match count #{matchesArray.size}"
#create a new regex using the match results; make sure to use auto escape method
originalPatternString = Regexp.escape(lineMatchCapture)
replacementRegex = Regexp.new(originalPatternString)
#replace any periods with underscores in a copy of lineMatchCapture
periodToUnderscoreCorrection = lineMatchCapture.gsub(/\./, '_')
#replace original match with underscore replaced copy within line
htmlLine.gsub!(replacementRegex, periodToUnderscoreCorrection)
puts "The modified htmlLine is now: #{htmlLine}"
}
end
}
I would think that I should get the first tag in matchData[0] then the second tag in matchData1, or, what I'm really doing because I don't know how many matches I'll get within any given line is matchData.to_a.each. And in this case, matchData has two captures, but they're both the first tag match
which is: <WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>
So, what the heck am I doing wrong, why does rubular test give me the expected results?
You want to use the on String#scan instead of the Regexp#match:
tag_regex = /<(?:WEBOBJECT|webobject) (?:NAME|name)=(?:[a-zA-Z0-9]+\.)+(?:[a-zA-Z0-9]+)(?:>)/
lines = "<WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>moreNonMatchingText\
<WEBOBJECT NAME=admin.SecondLineMatch>AndEvenMoreNonMatchingText"
lines.scan(tag_regex)
# => ["<WEBOBJECT NAME=admin.normalMode.someOtherPatternWeDontWant.moreThatWeDontWant>", "<WEBOBJECT NAME=admin.SecondLineMatch>"]
A few recommendations for next ruby questions:
newlines and spaces are your friends, you don't loose points for using more lines on your code ;-)
use do-end on blocks instead of {}, improves readability a lot
declare variables in snake case (hello_world) instead of camel case (helloWorld)
Hope this helps
I ended up using the String.scan approach, the only tricky point there was figuring out that this returns an array of arrays, not a MatchData object, so there was some initial confusion on my part, mostly due to my ruby green-ness, but it's working as expected now. Also, I trimmed the regex per Trevoke's suggestion. But snake case? Never...;-) Anyway, here goes:
tagRegex = /(<(?:webobject) (?:name)=(?:\w+\.)+(?:\w+)(?:>))/i
testFile = File.open('RegexTestingCompFix.txt', "r+")
lineCount=0
testFile.each do |htmlLine|
lineCount += 1
puts ("Current line: #{htmlLine} at line num: #{lineCount}")
oldMatches = htmlLine.scan(tagRegex) #oldMatches thusly named due to not explicitly using Regexp or MatchData, as in "the old way..."
if(oldMatches.size > 0)
oldMatches.each_index do |index|
arrayMatch = oldMatches[index]
aMatch = arrayMatch[0]
#create a new regex using the match results; make sure to use auto escape method
replacementRegex = Regexp.new(Regexp.escape(aMatch))
#replace any periods with underscores in a copy of lineMatchCapture
periodToUnderscoreCorrection = aMatch.gsub(/\./, '_')
#replace original match with underscore replaced copy within line, matching against the new escaped literal regex
htmlLine.gsub!(replacementRegex, periodToUnderscoreCorrection)
puts "The modified htmlLine is now: #{htmlLine}"
end # I kind of still prefer the brackets...;-)
end
end
Now, why does MatchData work the way it does? It seems like it's behavior is a bug really, and certainly not very useful in general if you can't get it provide a simple means of accessing all the matches. Just my $.02
Small bits:
This regexp helps you get "normalMode" .. But not "secondLineMatch":
<webobject name=\w+\.((?:\w+)).+> (with option 'i', for "case insensitive")
This regexp helps you get "secondLineMatch" ... But not "normalMode":
<webobject name=\w+\.((?:\w+))> (with option 'i', for "case insensitive").
I'm not really good at regexpt but I'll keep toiling at it.. :)
And I don't know if this helps you at all, but here's a way to get both:
<webobject name=admin.(\w+) (with option 'i').