How to read from stdin line by line in Node

Question

I m looking to process a text file with node using a command line call like   node app js  lt  input txt  Each line of the file needs to be processed individually  but once processed the input line can be forgotten   Using the on-data listener of the stdin  I get the input steam chunked by a byte size so I set this up   process stdin resume    process stdin setEncoding  utf8     var lingeringLine        process stdin on  data   function chunk        lines   chunk split   n         lines 0    lingeringLine   lines 0       lingeringLine   lines pop         lines forEach processLine        process stdin on  end   function         processLine lingeringLine         But this seems so sloppy  Having to massage around the first and last items of the lines array  Is there not a more elegant way to do this

User · Accepted Answer

You can use the readline module to read from stdin line by line   var readline   require  readline    var rl   readline createInterface     input  process stdin    output  process stdout    terminal  false      rl on  line   function line       console log line

User · Answer

process stdin pipe process stdout

User · Answer

if you want to ask the user number of lines first   x000D   x000D        array to save line by line      let xInputs            const getInput   async  resolve   gt               const readline   require  readline   createInterface                   input  process stdin                  output  process stdout                              readline on  line   line   gt               readline close                xInputs push line               resolve line                             const getMultiInput    numberOfInputLines callback   gt           let i   0          let p   Promise resolve             for    i  lt  numberOfInputLines  i                  p   p then     gt  new Promise resolve   gt  getInput resolve                       p then     gt               callback                             get number of lines      const readline   require  readline   createInterface           input  process stdin          output  process stdout          terminal  false             readline on  line   line   gt           getMultiInput line     gt                get here the inputs from xinputs array                      readline close           x000D   x000D   x000D

User · Answer

Work on POSIX and Windows var fs   require  fs    var stdinBuffer   fs readFileSync 0      STDIN FILENO   0 console log stdinBuffer toString

User · Answer

readline is specifically designed to work with terminal  that is process stdin isTTY     true   There are a lot of modules which provide split functionality for generic streams  like split  It makes things super-easy   process stdin pipe require  split      on  data   processLine   function processLine  line      console log line

User · Answer

In my case the program  elinks  returned lines that looked empty  but in fact had special terminal characters  color control codes and backspace  so grep options presented in other answers did not work for me  So I wrote this small script in Node js  I called the file tight  but that s just a random name      usr bin env node  function visible a        var R            for  var i   0  i  lt  a length  i              if  a i       b      R -  1  continue              if  a i       u001b                 while  a i      m   amp  amp  i  lt  a length  i               if  a i     undefined  break                   else R    a i            return  R    function empty a        a   visible a      for  var i   0  i  lt  a length  i              if  a i          return false           return  true    var readline   require  readline   var rl   readline createInterface   input  process stdin  output  process stdout  terminal  false     rl on  line   function line        if   empty line   console log line

User · Answer

usr bin env node  const EventEmitter   require  events     function stdinLineByLine       const stdin   new EventEmitter      let buff          process stdin      on  data   data   gt          buff    data        lines   buff split    r n  n           buff   lines pop          lines forEach line   gt  stdin emit  line   line                on  end        gt          if  buff length  gt  0  stdin emit  line   buff              return stdin     const stdin   stdinLineByLine    stdin on  line   console log

User · Answer

shareing for others   read stream line by line should be good for large files piped into stdin  my version   var n 0  function on line line cb            one each line     console log n    line   line       return cb            end of one each line    var fs   require  fs    var readStream   fs createReadStream  all titles txt      var readStream   process stdin  readStream pause    readStream setEncoding  utf8     var buffer     readStream on  data    chunk    gt        const newlines    r n         var lines chunk split newlines      if lines length  1                buffer push lines 0            return                buffer push lines 0        var str buffer join          buffer length 0      readStream pause         on line str     gt           var i 1 l lines length-1          i--          function while next                         i                if i lt l                                return on line lines i  while next                             else                               buffer push lines pop                     lines length 0                  return readStream resume                                    while next                 on  end       gt         if buffer length            var str buffer join                buffer length 0          on line str     gt                   after end             console error  done                   end after end                   readStream resume

[node.js] How to read from stdin line by line in Node

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