Highlight the difference between two strings in PHP

Question

What is the easiest way to highlight the difference between two strings in PHP   I m thinking along the lines of the Stack Overflow edit history page  where new text is in green and removed text is in red  If there are any pre-written functions or classes available  that would be ideal

User · Answer

What you are looking for is a  diff algorithm    A quick google search led me to this solution   I did not test it  but maybe it will do what you need

User · Answer

This is a nice one  also http   paulbutler org archives a-simple-diff-algorithm-in-php      Solving the problem is not as simple as it seems  and the problem bothered me for about a year before I figured it out  I managed to write my algorithm in PHP  in 18 lines of code  It is not the most efficient way to do a diff  but it is probably the easiest to understand       It works by finding the longest sequence of words common to both strings  and recursively finding the longest sequences of the remainders of the string until the substrings have no words in common  At this point it adds the remaining new words as an insertion and the remaining old words as a deletion       You can download the source here  PHP SimpleDiff

User · Answer

I had terrible trouble with the both the PEAR-based and the simpler alternatives shown  So here s a solution that leverages the Unix diff command  obviously  you have to be on a Unix system or have a working Windows diff command for it to work   Choose your favourite temporary directory  and change the exceptions to return codes if you prefer           brief Find the difference between two strings  lines assumed to be separated by   n      param  new string The new string     param  old string The old string     return string Human-readable output as produced by the Unix diff command     or  No changes  if the strings are the same      throws Exception     public static function diff  new   old       tempdir     var somewhere tmp      Your favourite temporary directory    oldfile   tempnam  tempdir  OLD       newfile   tempnam  tempdir  NEW      if    file put contents  oldfile  old         throw new Exception  diff failed to write temporary file                print r error get last   true          if    file put contents  newfile  new         throw new Exception  diff failed to write temporary file                print r error get last   true           answer   array       cmd    diff  newfile  oldfile     exec  cmd   answer   retcode     unlink  newfile     unlink  oldfile     if   retcode    1        throw new Exception  diff failed with return code      retcode         if  empty  answer         return  No changes       else       return implode   n    answer

User · Answer

If you want a robust library  Text Diff  a PEAR package  looks to be pretty good   It has some pretty cool features

User · Answer

There is also a PECL extension for xdiff    http   php net manual en book xdiff php http   pecl php net package xdiff   In particular    xdiff string diff     Make unified diff of two strings   Example from PHP Manual    lt  php  old article   file get contents    old article txt     new article     POST  article      diff   xdiff string diff  old article   new article  1   if  is string  diff         echo  Differences between two articles  n       echo  diff

User · Answer

I had terrible trouble with the both the PEAR-based and the simpler alternatives shown  So here s a solution that leverages the Unix diff command  obviously  you have to be on a Unix system or have a working Windows diff command for it to work   Choose your favourite temporary directory  and change the exceptions to return codes if you prefer           brief Find the difference between two strings  lines assumed to be separated by   n      param  new string The new string     param  old string The old string     return string Human-readable output as produced by the Unix diff command     or  No changes  if the strings are the same      throws Exception     public static function diff  new   old       tempdir     var somewhere tmp      Your favourite temporary directory    oldfile   tempnam  tempdir  OLD       newfile   tempnam  tempdir  NEW      if    file put contents  oldfile  old         throw new Exception  diff failed to write temporary file                print r error get last   true          if    file put contents  newfile  new         throw new Exception  diff failed to write temporary file                print r error get last   true           answer   array       cmd    diff  newfile  oldfile     exec  cmd   answer   retcode     unlink  newfile     unlink  oldfile     if   retcode    1        throw new Exception  diff failed with return code      retcode         if  empty  answer         return  No changes       else       return implode   n    answer

User · Answer

A php port of Neil Frasers diff match patch  Apache 2 0 licensed

User · Answer

I came across this PHP diff class by Chris Boulton based on Python difflib which could be a good solution   PHP Diff Lib

User · Answer

You were able to use the PHP Horde Text Diff package  However this package is no longer available

User · Answer

Just wrote a class to compute smallest  not to be taken literally  number of edits to transform one string into another string   http   www raymondhill net finediff   It has a static function to render a HTML version of the diff   It s a first version  and likely to be improved  but it works just fine as of now  so I am throwing it out there in case someone needs to generate a compact diff efficiently  like I needed   Edit  It s on Github now  https   github com gorhill PHP-FineDiff

User · Answer

Here is a short function you can use to diff two arrays  It implements the LCS algorithm   function computeDiff  from   to         diffValues   array         diffMask   array          dm   array         n1   count  from        n2   count  to        for   j   -1   j  lt   n2   j     dm -1   j    0      for   i   -1   i  lt   n1   i     dm  i  -1    0      for   i   0   i  lt   n1   i                  for   j   0   j  lt   n2   j                          if   from  i      to  j                                  ad    dm  i - 1   j - 1                    dm  i   j     ad   1                            else                                a1    dm  i - 1   j                    a2    dm  i   j - 1                    dm  i   j    max  a1   a2                                       i    n1 - 1       j    n2 - 1      while    i  gt  -1       j  gt  -1                 if   j  gt  -1                        if   dm  i   j - 1      dm  i   j                                  diffValues      to  j                    diffMask     1                   j--                    continue                                                if   i  gt  -1                        if   dm  i - 1   j      dm  i   j                                  diffValues      from  i                    diffMask     -1                   i--                  continue                                                               diffValues      from  i                diffMask     0               i--               j--                            diffValues   array reverse  diffValues        diffMask   array reverse  diffMask        return array  values    gt   diffValues   mask    gt   diffMask       It generates two arrays     values array  a list of elements as they appear in the diff  mask array  contains numbers  0  unchanged  -1  removed  1  added    If you populate an array with characters  it can be used to compute inline difference  Now just a single step to highlight the differences   function diffline  line1   line2         diff   computeDiff str split  line1   str split  line2         diffval    diff  values         diffmask    diff  mask          n   count  diffval        pmc   0       result           for   i   0   i  lt   n   i                   mc    diffmask  i           if   mc     pmc                        switch   pmc                                case -1   result      lt  del gt    break                  case 1   result      lt  ins gt    break                            switch   mc                                case -1   result      lt del gt    break                  case 1   result      lt ins gt    break                                   result     diffval  i             pmc    mc            switch   pmc                case -1   result      lt  del gt    break          case 1   result      lt  ins gt    break             return  result      Eg    echo diffline  StackOverflow    ServerFault     Will output   S lt del gt tackO lt  del gt  lt ins gt er lt  ins gt ver lt del gt f lt  del gt  lt ins gt Fau lt  ins gt l lt del gt ow lt  del gt  lt ins gt t lt  ins gt     StackOerverfFaulowt   Additional notes    The diff matrix requires  m 1   n 1  elements  So you can run into out of memory errors if you try to diff long sequences  In this case diff larger chunks  eg  lines  first  then diff their contents in a second pass  The algorithm can be improved if you trim the matching elements from the beginning and the end  then run the algorithm on the differing middle only  A latter  more bloated  version contains these modifications too

User · Answer

I would recommend looking at these awesome functions from PHP core   similar text     Calculate the similarity between two strings  http   www php net manual en function similar-text php  levenshtein     Calculate Levenshtein distance between two strings  http   www php net manual en function levenshtein php  soundex     Calculate the soundex key of a string  http   www php net manual en function soundex php  metaphone     Calculate the metaphone key of a string  http   www php net manual en function metaphone php

User · Answer

You were able to use the PHP Horde Text Diff package  However this package is no longer available

User · Answer

There is also a PECL extension for xdiff    http   php net manual en book xdiff php http   pecl php net package xdiff   In particular    xdiff string diff     Make unified diff of two strings   Example from PHP Manual    lt  php  old article   file get contents    old article txt     new article     POST  article      diff   xdiff string diff  old article   new article  1   if  is string  diff         echo  Differences between two articles  n       echo  diff

User · Answer

Just wrote a class to compute smallest  not to be taken literally  number of edits to transform one string into another string   http   www raymondhill net finediff   It has a static function to render a HTML version of the diff   It s a first version  and likely to be improved  but it works just fine as of now  so I am throwing it out there in case someone needs to generate a compact diff efficiently  like I needed   Edit  It s on Github now  https   github com gorhill PHP-FineDiff

User · Answer

This is a nice one  also http   paulbutler org archives a-simple-diff-algorithm-in-php      Solving the problem is not as simple as it seems  and the problem bothered me for about a year before I figured it out  I managed to write my algorithm in PHP  in 18 lines of code  It is not the most efficient way to do a diff  but it is probably the easiest to understand       It works by finding the longest sequence of words common to both strings  and recursively finding the longest sequences of the remainders of the string until the substrings have no words in common  At this point it adds the remaining new words as an insertion and the remaining old words as a deletion       You can download the source here  PHP SimpleDiff

User · Answer

A php port of Neil Frasers diff match patch  Apache 2 0 licensed

User · Answer

This is the best one I ve found   http   code stephenmorley org php diff-implementation

User · Answer

What you are looking for is a  diff algorithm    A quick google search led me to this solution   I did not test it  but maybe it will do what you need

User · Answer

If you want a robust library  Text Diff  a PEAR package  looks to be pretty good   It has some pretty cool features

User · Answer

I came across this PHP diff class by Chris Boulton based on Python difflib which could be a good solution   PHP Diff Lib

User · Answer

You were able to use the PHP Horde Text Diff package  However this package is no longer available

User · Answer

If you want a robust library  Text Diff  a PEAR package  looks to be pretty good   It has some pretty cool features

User · Answer

You were able to use the PHP Horde Text Diff package  However this package is no longer available

User · Answer

Another solution  for side-by-side comparison as opposed to a unified view   https   github com danmysak side-by-side

User · Answer

If you want a robust library  Text Diff  a PEAR package  looks to be pretty good   It has some pretty cool features

User · Answer

I would recommend looking at these awesome functions from PHP core   similar text     Calculate the similarity between two strings  http   www php net manual en function similar-text php  levenshtein     Calculate Levenshtein distance between two strings  http   www php net manual en function levenshtein php  soundex     Calculate the soundex key of a string  http   www php net manual en function soundex php  metaphone     Calculate the metaphone key of a string  http   www php net manual en function metaphone php

User · Answer

Another solution  for side-by-side comparison as opposed to a unified view   https   github com danmysak side-by-side

User · Answer

What you are looking for is a  diff algorithm    A quick google search led me to this solution   I did not test it  but maybe it will do what you need

User · Answer

Here is a short function you can use to diff two arrays  It implements the LCS algorithm   function computeDiff  from   to         diffValues   array         diffMask   array          dm   array         n1   count  from        n2   count  to        for   j   -1   j  lt   n2   j     dm -1   j    0      for   i   -1   i  lt   n1   i     dm  i  -1    0      for   i   0   i  lt   n1   i                  for   j   0   j  lt   n2   j                          if   from  i      to  j                                  ad    dm  i - 1   j - 1                    dm  i   j     ad   1                            else                                a1    dm  i - 1   j                    a2    dm  i   j - 1                    dm  i   j    max  a1   a2                                       i    n1 - 1       j    n2 - 1      while    i  gt  -1       j  gt  -1                 if   j  gt  -1                        if   dm  i   j - 1      dm  i   j                                  diffValues      to  j                    diffMask     1                   j--                    continue                                                if   i  gt  -1                        if   dm  i - 1   j      dm  i   j                                  diffValues      from  i                    diffMask     -1                   i--                  continue                                                               diffValues      from  i                diffMask     0               i--               j--                            diffValues   array reverse  diffValues        diffMask   array reverse  diffMask        return array  values    gt   diffValues   mask    gt   diffMask       It generates two arrays     values array  a list of elements as they appear in the diff  mask array  contains numbers  0  unchanged  -1  removed  1  added    If you populate an array with characters  it can be used to compute inline difference  Now just a single step to highlight the differences   function diffline  line1   line2         diff   computeDiff str split  line1   str split  line2         diffval    diff  values         diffmask    diff  mask          n   count  diffval        pmc   0       result           for   i   0   i  lt   n   i                   mc    diffmask  i           if   mc     pmc                        switch   pmc                                case -1   result      lt  del gt    break                  case 1   result      lt  ins gt    break                            switch   mc                                case -1   result      lt del gt    break                  case 1   result      lt ins gt    break                                   result     diffval  i             pmc    mc            switch   pmc                case -1   result      lt  del gt    break          case 1   result      lt  ins gt    break             return  result      Eg    echo diffline  StackOverflow    ServerFault     Will output   S lt del gt tackO lt  del gt  lt ins gt er lt  ins gt ver lt del gt f lt  del gt  lt ins gt Fau lt  ins gt l lt del gt ow lt  del gt  lt ins gt t lt  ins gt     StackOerverfFaulowt   Additional notes    The diff matrix requires  m 1   n 1  elements  So you can run into out of memory errors if you try to diff long sequences  In this case diff larger chunks  eg  lines  first  then diff their contents in a second pass  The algorithm can be improved if you trim the matching elements from the beginning and the end  then run the algorithm on the differing middle only  A latter  more bloated  version contains these modifications too

User · Answer

What you are looking for is a  diff algorithm    A quick google search led me to this solution   I did not test it  but maybe it will do what you need

User · Answer

This is the best one I ve found   http   code stephenmorley org php diff-implementation

[php] Highlight the difference between two strings in PHP

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