Regular expression to get a string between two strings in Javascript

Question

I have found very similar posts  but I can t quite get my regular expression right here   I am trying to write a regular expression which returns a string which is between two other strings  For example  I want to get the string which resides between the strings  cow  and  milk       My cow always gives milk   would return      always gives    Here is the expression I have pieced together so far      cow      milk    However  this returns the string  cow always gives

User · Answer

You need capture the    You can  but don t have to  make the    nongreedy There s really no need for the lookahead    gt   cow     milk i exec  My cow always gives milk      cow always gives milk     always gives

User · Answer

You can use the method match   to extract a substring between two strings  Try the following code  var str    quot My cow always gives milk quot   var subStr   str match  quot cow    milk quot    console log subStr 1     Output   always gives  See a complete example here   How to find sub-string between two strings

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Just use the following regular expression      lt  My cow s        smilk

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Task  Extract substring between two string  excluding this two strings   Solution  let allText    Lorem Ipsum is simply dummy text of the printing and typesetting industry  Lorem Ipsum has been the industry s standard dummy text ever since the 1500s  when an unknown printer took a galley of type and scrambled it to make a type specimen book  It has survived not only five centuries  but also the leap into electronic typesetting  remaining essentially unchanged  It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages  and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum   let textBefore    five centuries    let textAfter    electronic typesetting   var regExp   new RegExp     lt    textBefore   s           s   textAfter      g    var results   regExp exec allText   if  results  amp  amp  results length  gt  1        console log results 0

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Here s a regex which will grab what s between cow and milk  without leading trailing space    srctext    My cow always gives milk    var re       cow s        s milk      var newtext   srctext replace re    2      An example  http   jsfiddle net entropo tkP74

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I was able to get what I needed using Martinho Fernandes  solution below  The code is   var test    My cow always gives milk    var testRE   test match  cow    milk    alert testRE 1      You ll notice that I am alerting the testRE variable as an array  This is because testRE is returning as an array  for some reason  The output from   My cow always gives milk   Changes into   always gives

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You can use destructuring to only focus on the part of your interest  So you can do   x000D   x000D  let str    My cow always gives milk    let    result    str match   bcow s       s milk b           console log result   x000D   x000D   x000D   In this way you ignore the first part  the complete match  and only get the capture group s match  The addition of       may be interesting if you are not sure there will be a match at all  In that case match would return null which cannot be destructured  and so we return    instead in that case  and then result will be null  The additional  b ensures the surrounding words  quot cow quot  and  quot milk quot  are really separate words  e g  not  quot milky quot    Also  s  is needed to avoid that the match includes some outer spacing

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The method match   searches a string for a match and returns an Array object      Original string var str    My cow always gives milk       Using index  0  would return lt br  gt        cow always gives milk    str match  cow    milk     0         Using index    1    would return       always gives    str match  cow    milk   1

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A lookahead  that     part  does not consume any input  It is a zero-width assertion  as are boundary checks and lookbehinds    You want a regular match here  to consume the cow portion  To capture the portion in between  you use a capturing group  just put the portion of pattern you want to capture inside parenthesis      cow    milk   No lookaheads are needed at all

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I find regex to be tedious and time consuming given the syntax  Since you are already using javascript it is easier to do the following without regex    const text    My cow always gives milk  const start    cow   const end    milk   const middleText   text split start  1  split end  0  console log middleText     prints  always gives

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Regular expression to get a string between two strings in JavaScript  The most complete solution that will work in the vast majority of cases is using a capturing group with a lazy dot matching pattern  However  a dot   in JavaScript regex does not match line break characters  so  what will work in 100  cases is a     or   s S    d D    w W  constructs  ECMAScript 2018 and newer compatible solution In JavaScript environments supporting ECMAScript 2018  s modifier allows   to match any char including line break chars  and the regex engine supports lookbehinds of variable length  So  you may use a regex like var result   s match     lt  cow s         s milk  gs      Returns multiple matches if any    Or var result   s match     lt  cow s         s milk  gs      Same but whitespaces are optional  In both cases  the current position is checked for cow with any 1 0 or more whitespaces after cow  then any 0  chars as few as possible are matched and consumed   added to the match value   and then milk is checked for  with any 1 0 or more whitespaces before this substring   Scenario 1  Single-line input This and all other scenarios below are supported by all JavaScript environments  See usage examples at the bottom of the answer  cow       milk  cow is found first  then a space  then any 0  chars other than line break chars  as few as possible as    is a lazy quantifier  are captured into Group 1 and then a space with milk must follow  and those are matched and consumed  too   Scenario 2  Multiline input cow    s S     milk  Here  cow and a space are matched first  then any 0  chars as few as possible are matched and captured into Group 1  and then a space with milk are matched  Scenario 3  Overlapping matches If you have  a string like  gt  gt  gt 15 text gt  gt  gt 67 text2 gt  gt  gt  and you need to get 2 matches in-between  gt  gt  gt  number whitespace and  gt  gt  gt   you can t use   gt  gt  gt  d  s      gt  gt  gt  g as this will only find 1 match due to the fact the  gt  gt  gt  before 67 is already consumed upon finding the first match  You may use a positive lookahead to check for the text presence without actually  quot gobbling quot  it  i e  appending to the match     gt  gt  gt  d  s         gt  gt  gt   g  See the online regex demo yielding text1 and text2 as Group 1 contents found  Also see How to get all possible overlapping matches for a string  Performance considerations Lazy dot matching pattern       inside regex patterns may slow down script execution if very long input is given  In many cases  unroll-the-loop technique helps to a greater extent  Trying to grab all between cow and milk from  quot Their ncow ngives nmore nmilk quot   we see that we just need to match all lines that do not start with milk  thus  instead of cow n   s S     nmilk we can use   cow n       n   milk        nmilk gm  See the regex demo  if there can be  r n  use  cow r  n       r  n   milk        r  nmilk gm   With this small test string  the performance gain is negligible  but with very large text  you will feel the difference  especially if the lines are long and line breaks are not very numerous    Sample regex usage in JavaScript   x000D   x000D    Single First match expected  use no global modifier and access match 1  console log  My cow always gives milk  match  cow       milk   1       Multiple matches  get multiple matches with a global modifier and    trim the results if length of leading trailing delimiters is known var s    My cow always gives milk  thier cow also gives milk   console log s match  cow       milk g  map function x   return x substr 4 x length-9         or use RegExp exec inside a loop to collect all the Group 1 contents var result       m  rx    cow       milk g  while   m rx exec s       null      result push m 1      console log result   x000D   x000D   x000D     Using the modern String matchAll method  x000D   x000D  const s    My cow always gives milk  thier cow also gives milk   const matches   s matchAll  cow       milk g   console log Array from matches  x   gt  x 1     x000D   x000D   x000D

User · Answer

The chosen answer didn t work for me   hmm     Just add space after cow and or before milk to trim spaces from   always gives        lt  cow        milk

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If the data is on multiple lines then you may have to use the following    My cow    s S   milk gm  My cow always gives  milk   Regex 101 example

[javascript] Regular expression to get a string between two strings in Javascript

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