Replace a string in a file with nodejs

Question

I use the md5 grunt task to generate MD5 filenames  Now I want to rename the sources in the HTML file with the new filename in the callback of the task  I wonder what s the easiest way to do this

User · Answer

Since replace wasn t working for me  I ve created a simple npm package replace-in-file to quickly replace text in one or more files  It s partially based on  asgoth s answer   Edit  3 October 2016   The package now supports promises and globs  and the usage instructions have been updated to reflect this   Edit  16 March 2018   The package has amassed over 100k monthly downloads now and has been extended with additional features as well as a CLI tool   Install   npm install replace-in-file   Require module  const replace   require  replace-in-file      Specify replacement options  const options          Single file   files   path to file        Multiple files   files         path to file        path to other file             Glob s     files         path to files   html        another      path             Replacement to make  string or regex     from   Find me g    to   Replacement        Asynchronous replacement with promises   replace options     then changedFiles   gt        console log  Modified files    changedFiles join                 catch error   gt        console error  Error occurred    error           Asynchronous replacement with callback   replace options   error  changedFiles    gt      if  error        return console error  Error occurred    error         console log  Modified files    changedFiles join               Synchronous replacement   try     let changedFiles   replace sync options     console log  Modified files    changedFiles join           catch  error      console error  Error occurred    error

User · Answer

Expanding on  Sanbor s answer  the most efficient way to do this is to read the original file as a stream  and then also stream each chunk into a new file  and then lastly replace the original file with the new file   async function findAndReplaceFile regexFindPattern  replaceValue  originalFile      const updatedFile      originalFile  updated      return new Promise  resolve  reject    gt        const readStream   fs createReadStream originalFile    encoding   utf8   autoClose  true         const writeStream   fs createWriteStream updatedFile    encoding   utf8   autoClose  true             For each chunk  do the find  amp  replace  and write it to the new file stream     readStream on  data    chunk    gt          chunk   chunk toString   replace regexFindPattern  replaceValue         writeStream write chunk                   Once we ve finished reading the original file        readStream on  end        gt          writeStream end       emits  finish  event  executes below statement                 Replace the original file with the updated file     writeStream on  finish   async      gt          try           await  renameFile originalFile  updatedFile           resolve            catch  error            reject  Error  Error renaming   originalFile  to   updatedFile    gt    error message                          readStream on  error    error    gt  reject  Error  Error reading   originalFile    gt    error message          writeStream on  error    error    gt  reject  Error  Error writing to   updatedFile    gt    error message               async function  renameFile oldPath  newPath      return new Promise  resolve  reject    gt        fs rename oldPath  newPath   error    gt          if  error            reject error           else           resolve                                Testing it     async      gt      try       await findAndReplaceFile   some regex  g   someReplaceValue    someFilePath        catch error        console log error

User · Answer

You could process the file while being read by using streams  It s just like using buffers but with a more convenient API   var fs   require  fs    function searchReplaceFile regexpFind  replace  cssFileName        var file   fs createReadStream cssFileName   utf8        var newCss            file on  data   function  chunk            newCss    chunk toString   replace regexpFind  replace                file on  end   function              fs writeFile cssFileName  newCss  function err                if  err                    return console log err                 else                   console log  Updated                                searchReplaceFile  foo g   bar    file txt

User · Answer

On Linux or Mac  keep is simple and just use sed with the shell  No external libraries required  The following code works on Linux   const shell   require  child process   execSync shell  sed -i  s oldString newString g    yourFile js     The sed syntax is a little different on Mac  I can t test it right now  but I believe you just need to add an empty string after the  -i    const shell   require  child process   execSync shell  sed -i     s oldString newString g    yourFile js     The  g  after the final     makes sed replace all instances on a line  Remove it  and only the first occurrence per line will be replaced

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ES2017 8 for Node 7 6  with a temporary write file for atomic replacement   const Promise   require  bluebird   const fs   Promise promisifyAll require  fs     async function replaceRegexInFile file  search  replace     let contents   await fs readFileAsync file   utf8     let replaced contents   contents replace search  replace    let tmpfile      file  jstmpreplace    await fs writeFileAsync tmpfile  replaced contents   utf8     await fs renameAsync tmpfile  file    return true     Note  only for smallish files as they will be read into memory

User · Answer

You can also use the  sed  function that s part of ShellJS         npm install  -g  shelljs    require  shelljs global     sed  -i    search pattern    replace pattern   file     Visit ShellJs org for more examples

User · Answer

I ran into issues when replacing a small placeholder with a large string of code   I was doing   var replaced   original replace  PLACEHOLDER   largeStringVar     I figured out the problem was JavaScript s special replacement patterns  described here  Since the code I was using as the replacing string had some   in it  it was messing up the output   My solution was to use the function replacement option  which DOES NOT do any special replacement   var replaced   original replace  PLACEHOLDER   function         return largeStringVar

User · Answer

Perhaps the  replace  module  www npmjs org package replace  also would work for you   It would not require you to read and then write the file   Adapted from the documentation      install   npm install replace      require   var replace   require  replace        use   replace       regex   string to be replaced       replacement   replacement string       paths    path to your file        recursive  true      silent  true

User · Answer

I would use a duplex stream instead  like documented here nodejs doc duplex streams     A Transform stream is a Duplex stream where the output is computed in   some way from the input

User · Answer

This may help someone  This is a little different than just a global replace from the terminal we run node replace js replace js  function processFile inputFile  repString    quot     quot     var fs   require  fs        readline   require  readline        instream   fs createReadStream inputFile       outstream   new  require  stream           rl   readline createInterface instream  outstream       formatted           const regex     lt xsl include href  quot     quot     quot     gt   gm   rl on  line   function  line        let url           let m      while   m   regex exec line       null               This is necessary to avoid infinite loops with zero-width matches         if  m index     regex lastIndex                regex lastIndex                               url   m 1              let re   new RegExp       lt xsl include href  quot       quot     gt        gm         formatted    line replace re    t lt xsl include href  quot   repString   url  quot    gt         formatted     quot  n quot        rl on  close   function  line        fs writeFile inputFile  formatted   utf8   function  err            if  err  return console log err                       path is relative to where your running the command from processFile  build some xslt     This is what this does  We have several file that have xml includes However in development we need the path to move down a level  From this  lt xsl include href  quot common some xslt quot    gt   to this  lt xsl include href  quot    common some xslt quot    gt   So we end up running two regx patterns one to get the href and the other to write there is probably a better way to do this but it work for now  Thanks

User · Answer

You could use simple regex   var result   fileAsString replace  string to be replaced g   replacement      So     var fs   require  fs   fs readFile someFile   utf8   function  err data      if  err        return console log err         var result   data replace  string to be replaced g   replacement       fs writeFile someFile  result   utf8   function  err         if  err  return console log err

User · Answer

lt p gt Please click in the following   link   to verify the account lt  p gt    function renderHTML templatePath  string  object        const template   fileSystem readFileSync path join Application staticDirectory  templatePath     html     utf8        return template match              ig  reduce  acc  binding    gt            const property   binding substring 2  binding length - 2           return    acc   template replace                object property                      renderHTML templateName    link   SomeLink       for sure you can improve the reading template function to read as stream and compose the bytes by line to make it more efficient

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