Read a text file using Node js

Question

I need to pass in a text file in the terminal and then read the data from it  how can I do this   node server js file txt   How do I pass in the path from the terminal  how do I read that on the other side

User · Answer

The async way of life      usr bin node  const fs   require  fs     function readall  stream      return new Promise   resolve  reject    gt        const chunks           stream on   error    error    gt  reject  error        stream on   data     chunk    gt  chunk  amp  amp  chunks push  chunk        stream on   end               gt  resolve  Buffer concat  chunks              function readfile  filename      return readall  fs createReadStream  filename        async      gt      let content   await readfile    etc ssh moduli   catch   e    gt        if  content      console log   quot size  quot   content length                    quot head  quot   content slice  0  46  toString

User · Answer

You ll want to use the process argv array to access the command-line arguments to get the filename and the FileSystem module  fs  to read the file   For example      Make sure we got a filename on the command line  if  process argv length  lt  3      console log  Usage  node     process argv 1      FILENAME      process exit 1        Read the file and print its contents  var fs   require  fs       filename   process argv 2   fs readFile filename   utf8   function err  data      if  err  throw err    console log  OK      filename     console log data        To break that down a little for you process argv will usually have length two  the zeroth item being the  node  interpreter and the first being the script that node is currently running  items after that were passed on the command line   Once you ve pulled a filename from argv then you can use the filesystem functions to read the file and do whatever you want with its contents   Sample usage would look like this     node   cat js file txt OK  file txt This is file txt     Edit  As  wtfcoder mentions  using the  fs readFile    method might not be the best idea because it will buffer the entire contents of the file before yielding it to the callback function   This buffering could potentially use lots of memory but  more importantly  it does not take advantage of one of the core features of node js - asynchronous  evented I O   The  node  way to process a large file  or any file  really  would be to use fs read   and process each available chunk as it is available from the operating system   However  reading the file as such requires you to do your own  possibly  incremental parsing processing of the file and some amount of buffering might be inevitable

User · Answer

IMHO  fs readFile   should be avoided because it loads ALL the file in memory and it won t call the callback until all the file has been read   The easiest way to read a text file is to read it line by line  I recommend a BufferedReader   new BufferedReader   file     encoding   utf8          on   error   function  error           console log   error      error               on   line   function  line           console log   line      line               on   end   function             console log   EOF                read       For complex data structures like  properties or json files you need to use a parser  internally it should also use a buffered reader

User · Answer

I am posting a complete example which I finally got working  Here I am reading in a file rooms rooms txt from a script rooms rooms js  var fs   require  fs    var path   require  path    var readStream   fs createReadStream path join   dirname      rooms       rooms txt    utf8    let data      readStream on  data   function chunk        data    chunk     on  end   function         console log data

User · Answer

Usign fs with node   var fs   require  fs     try         var data   fs readFileSync  file txt    utf8        console log data toString           catch e        console log  Error    e stack

User · Answer

You can use readstream and pipe to read the file line by line without read all the file into memory one time   var fs   require  fs        es   require  event-stream        os   require  os     var s   fs createReadStream path       pipe es split         pipe es mapSync function line              pause the readstream         s pause            console log  line    line           s resume                on  error   function err            console log  Error    err               on  end   function             console log  Finish reading

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