Say I have a string: Hey what's up @dude, @how's it going?
I'd like to remove all the characters before@how's.
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7 Answers
or with the regex:
str = "Hey what's up @dude, @how's it going?"
str.gsub!(/.*?(?=@how)/im, "") #=> "@how's it going?"
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answered Mar 31, 2011 at 14:28
Vasiliy Ermolovich
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5 Comments
oxo
Considering that it could be in any case variation of @how (e.g. @How, @HOW, @HoW etc), could it be done like this: str.gsub(/.*?(?=@[Hh][Oo][Ww])/, "")?
Vasiliy Ermolovich
sure, fixed. (/i have been added)
Phrogz
No need for
gsub! when sub! will do, right? Also note (per my answer) that you need the \A anchor and/or m flag in case the string has a newline before the text to match.Vasiliy Ermolovich
Thanks! Sorry, I don't know the difference between gsub and sub. Could you explain it?
Andrew Haust
Suuuuper old and you obviously probably know the difference by now, but would be nice to see the answer changed for n00bs: gsub does a global search and replace while sub stops after the first match. gsub could cause unexpected results or poor performance is longer strings.
Use String#slice
s = "Hey what's up @dude, @how's it going?"
s.slice(s.index("@how")..-1)
# => "@how's it going?"
5 Comments
McStretch
+1 very clean. Aren't the indices off though? Shouldn't it be
0..s.index("@how")?
Simone Carletti
He wants to strip everything before the match, that is the same to say "keep everything after the match".
McStretch
Oh whoops, I misunderstood how splice worked. I thought it removed the string in place, like a delete method. I didn't realize it returned the spliced text for use.
oxo
I commented below to another answer, but I was wondering that since it could be in any case variation of @how (e.g. @How, @HOW, @HoW etc), could it be done like this: str.slice(str.index("@[Hh][Oo][Ww]")..-1)
Nathan Long
If the search string doesn't appear, the
index will return nil. So he should either check for nil before doing the slice, or plan to rescue the error that comes from passing an index of nil to slice.There are literally tens of ways of doing this. Here are the ones I would use:
If you want to preserve the original string:
str = "Hey what's up @dude, @how's it going?"
str2 = str[/@how's.+/mi]
p str, str2
#=> "Hey what's up @dude, @how's it going?"
#=> "@how's it going?"
If you want to mutate the original string:
str = "Hey what's up @dude, @how's it going?"
str[/\A.+?(?=@how's)/mi] = ''
p str
#=> "@how's it going?"
...or...
str = "Hey what's up @dude, @how's it going?"
str.sub! /\A.+?(?=@how's)/mi, ''
p str
#=> "@how's it going?"
You need the \A to anchor at the start of the string, and the m flag to ensure that you are matching across multiple lines.
Perhaps simplest of all for mutating the original:
str = "Hey what's up @dude, @how's it going?"
str.replace str[/@how's.+/mi]
p str
#=> "@how's it going?"
Comments
String#slice and String#index work fine but will blow up with ArgumentError: bad value for range if the needle is not in the haystack.
Using String#partition or String#rpartition might work better in that case:
s.partition "@how's"
# => ["Hey what's up @dude, ", "@how's", " it going?"]
s.partition "not there"
# => ["Hey what's up @dude, @how's it going?", "", ""]
s.rpartition "not there"
# => ["", "", "Hey what's up @dude, @how's it going?"]
Comments
An easy way to get only the part you are interested in.
>> s="Hey what's up @dude, @how's it going?"
=> "Hey what's up @dude, @how's it going?"
>> s[/@how.*$/i]
=> "@how's it going?"
If you really need to change the string object, you could always do s=s[...].
Comments
>> "Hey what's up @dude, @how's it going?".partition("@how's")[-2..-1].join
=> "@how's it going?"
Case insensitive
>> "Hey what's up @dude, @HoW's it going?".partition(/@how's/i)[-2..-1].join
=> "@HoW's it going?"
Or using scan()
>> "Hey what's up @dude, @HoW's it going?".scan(/@how's.*/i)[0]
=> "@HoW's it going?"
1 Comment
Phrogz
You need a
m flag on that last regex to match any newlines that may follow.You can also directly call [] also on a string(same as slice)
s = "Hey what's up @dude, @how's it going?"
start_index = s.downcase.index("@how")
start_index ? s[start_index..-1] : ""
