Read and write a String from text file

Question

I need to read and write data to from a text file  but I haven t been able to figure out how   I found this sample code in the Swift s iBook  but I still don t know how to write or read data   import Cocoa  class DataImporter              DataImporter is a class to import data from an external file      The class is assumed to take a non-trivial amount of time to initialize             var fileName    data txt         the DataImporter class would provide data importing functionality here    class DataManager        lazy var importer   DataImporter       var data   String            the DataManager class would provide data management functionality here    let manager   DataManager   manager data     Some data  manager data     Some more data     the DataImporter instance for the importer property has not yet been created     println manager importer fileName     the DataImporter instance for the importer property has now been created    prints  data txt       var str    Hello World in Swift Language

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write in ViewDidLoad  var error  NSError  var paths   NSSearchPathForDirectoriesInDomains  DocumentDirectory  NSSearchPathDomainMask UserDomainMask  true  var documentsDirectory   paths first as String var dataPath   documentsDirectory stringByAppendingPathComponent  MyFolder    if  NSFileManager defaultManager   fileExistsAtPath dataPath        NSFileManager defaultManager   createDirectoryAtPath dataPath  withIntermediateDirectories  false  attributes  nil  error   amp error    else       println  not creted or exist      func listDocumentDirectoryfiles   - gt   String        if let documentDirectory   NSSearchPathForDirectoriesInDomains  DocumentDirectory   UserDomainMask  true  first as  String           let myFilePath   documentDirectory stringByAppendingPathComponent  MyFolder           return NSFileManager defaultManager   contentsOfDirectoryAtPath myFilePath  error  nil  as  String            return

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Earlier solutions answers question  but in my case deleting old content of file while writing was a problem    So  I created piece of code for writing to file in documents directory without deleting previous content  You probably need better error handling  but I believe it s good starting point  Swift 4  Usuage       let filename    test txt      createOrOverwriteEmptyFileInDocuments filename  filename      if let handle   getHandleForFileInDocuments filename  filename            writeString string   aaa   fileHandle  handle          writeString string   bbb   fileHandle  handle          writeString string    n   fileHandle  handle          writeString string   ccc   fileHandle  handle          Helper methods   func createOrOverwriteEmptyFileInDocuments filename  String       guard let dir   FileManager default urls for   documentDirectory  in   userDomainMask  first else           debugPrint  ERROR IN createOrOverwriteEmptyFileInDocuments           return           let fileURL   dir appendingPathComponent filename      do           try    write to  fileURL  atomically  true  encoding   utf8            catch           debugPrint  ERROR WRITING STRING      error localizedDescription            debugPrint  FILE CREATED      fileURL absoluteString     private func writeString string  String  fileHandle  FileHandle       let data   string data using  String Encoding utf8      guard let dataU   data else           debugPrint  ERROR WRITING STRING      string          return           fileHandle seekToEndOfFile       fileHandle write dataU     private func getHandleForFileInDocuments filename  String - gt FileHandle       guard let dir   FileManager default urls for   documentDirectory  in   userDomainMask  first else           debugPrint  ERROR OPENING FILE           return nil           let fileURL   dir appendingPathComponent filename      do           let fileHandle  FileHandle    try FileHandle forWritingTo  fileURL          return fileHandle           catch           debugPrint  ERROR OPENING FILE      error localizedDescription          return nil

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In the function example   read write DocumentsFromFile      having some function wrappers certainly seems to makes sense since everything in OSx and iOS seems to need three or four major classes instantiated and a bunch of  properties  configured  linked  instantiated  and set  just to write  Hi  to a file  in 182 countries     However  these examples aren t complete enough to use in a real program   The write function does not report any errors creating or writing to the file  On the read  I don t think it s a good idea to return an error that the file doesn t exist as the string that is supposed to contain the data that was read   You would want to know that it failed and why  through some notification mechanism  like an exception  Then  you can write some code that outputs what the problem is and allows the user to correct it  or  correctly  breaks the program at that point   You would not want to just return a string with an  Error file does not exist  in it  Then  you would have to look for the error in the string from calling function each time and handle it there   You also possibly couldn t really tell if the error string was actually read from an actual file  or if it was produced from your code   You can t even call the read like this in swift 2 2 and Xcode 7 3 because NSString contentsOfFile     throws an exception  It is a compile time error if you do not have any code to catch it and do something with it  like print it to stdout  or better  an error popup window  or stderr   I have heard that Apple is moving away from try catch and exceptions  but it s going to be a long move and it s not possible to write code without this   I don t know where the  amp error argument comes from  perhaps an older version  but NSString writeTo File URL  does not currently have an NSError argument  They are defined like this in NSString h    public func writeToURL url  NSURL  atomically useAuxiliaryFile  Bool  encoding enc  UInt  throws public func writeToFile path  String  atomically useAuxiliaryFile  Bool  encoding enc  UInt  throws public convenience init contentsOfURL url  NSURL  encoding enc  UInt  throws public convenience init contentsOfFile path  String  encoding enc  UInt  throws   Also  the file not existing is just one of a number of potential problems your program might have reading a file  such as a permissions problem  the file size  or numerous other issues that you would not even want to try to code a handler for each one of them   It s best to just assume it s all correct and catch and print  or handle  an exception if something goes amiss  besides  at this point  you don t really have a choice anyway   Here are my rewrites    func writeToDocumentsFile fileName String value String         let documentsPath   NSSearchPathForDirectoriesInDomains  DocumentDirectory   UserDomainMask  true  0  as NSString      let path   documentsPath stringByAppendingPathComponent fileName       do           try value writeToFile path  atomically  true  encoding  NSUTF8StringEncoding        catch let error as NSError           print  ERROR   writing to file   path      error localizedDescription              func readFromDocumentsFile fileName String  - gt  String        let documentsPath   NSSearchPathForDirectoriesInDomains  DocumentDirectory   UserDomainMask  true  0  as NSString     let path   documentsPath stringByAppendingPathComponent fileName       var readText   String           do           try readText   NSString contentsOfFile  path  encoding  NSUTF8StringEncoding  as String           catch let error as NSError           print  ERROR   reading from file   fileName      error localizedDescription              return readText

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I want to show you only the first part  that is read  Here s how simply you can read   Swift 3    let s   try String contentsOfFile  Bundle main path forResource   myFile   ofType   txt       Swift 2    let s   try  String contentsOfFile  NSBundle mainBundle   pathForResource  myFile   ofType   txt

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For reading and writing you should use a location that is writeable  for example documents directory  The following code shows how to read and write a simple string  You can test it on a playground   Swift 3 x - 5 x  let file    file txt    this is the file  we will write to and read from it  let text    some text    just a text  if let dir   FileManager default urls for   documentDirectory  in   userDomainMask  first        let fileURL   dir appendingPathComponent file         writing     do           try text write to  fileURL  atomically  false  encoding   utf8            catch     error handling here            reading     do           let text2   try String contentsOf  fileURL  encoding   utf8            catch     error handling here         Swift 2 2  let file    file txt    this is the file  we will write to and read from it  let text    some text    just a text  if let dir   NSSearchPathForDirectoriesInDomains NSSearchPathDirectory DocumentDirectory  NSSearchPathDomainMask AllDomainsMask  true  first       let path   NSURL fileURLWithPath  dir  URLByAppendingPathComponent file         writing     do           try text writeToURL path  atomically  false  encoding  NSUTF8StringEncoding            catch     error handling here            reading     do           let text2   try NSString contentsOfURL  path  encoding  NSUTF8StringEncoding            catch     error handling here         Swift 1 x  let file    file txt   if let dirs    String    NSSearchPathForDirectoriesInDomains NSSearchPathDirectory DocumentDirectory  NSSearchPathDomainMask AllDomainsMask  true  as   String        let dir   dirs 0    documents directory     let path   dir stringByAppendingPathComponent file       let text    some text         writing     text writeToFile path  atomically  false  encoding  NSUTF8StringEncoding  error  nil          reading     let text2   String contentsOfFile  path  encoding  NSUTF8StringEncoding  error  nil

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Latest swift3 code You can read data from text file just use bellow code This my text file           NumberOfSlices    8    NrScenes    5    Scenes                  dataType    label1               image   http   is3 mzstatic com image thumb Purple19 v4 6e 81 31 6e8131cf-2092-3cd3-534c-28e129897ca9 mzl syvaewyp png 53x53bb-85 png                value    Hello               color     UIColor red                               dataType    label2               image   http   is1 mzstatic com image thumb Purple71 v4 6c 4c c1 6c4cc1bc-8f94-7b13-f3aa-84c41443caf3 mzl hcqvmrix png 53x53bb-85 png               value    Hi There               color     UIColor blue                               dataType    label3               image   http   is1 mzstatic com image thumb Purple71 v4 6c 4c c1 6c4cc1bc-8f94-7b13-f3aa-84c41443caf3 mzl hcqvmrix png 53x53bb-85 png                value    hi how r u                color     UIColor green                               dataType    label4               image   http   is1 mzstatic com image thumb Purple71 v4 6c 4c c1 6c4cc1bc-8f94-7b13-f3aa-84c41443caf3 mzl hcqvmrix png 53x53bb-85 png               value    what are u doing                 color     UIColor purple                               dataType    label5              image   http   is1 mzstatic com image thumb Purple71 v4 6c 4c c1 6c4cc1bc-8f94-7b13-f3aa-84c41443caf3 mzl hcqvmrix png 53x53bb-85 png               value    how many times                color     UIColor white                               dataType    label6               image   http   is1 mzstatic com image thumb Purple71 v4 5a f3 06 5af306b0-7cac-1808-f440-bab7a0d18ec0 mzl towjvmpm png 53x53bb-85 png               value    hi how r u                color     UIColor blue                               dataType    label7               image   http   is5 mzstatic com image thumb Purple71 v4 a8 dc eb a8dceb29-6daf-ca0f-d037-df9f34cdc476 mzl ukhhsxik png 53x53bb-85 png               value    hi how r u                color     UIColor gry                               dataType    label8               image   http   is2 mzstatic com image thumb Purple71 v4 15 23 e0 1523e03c-fff2-291e-80a7-73f35d45c7e5 mzl zejcvahm png 53x53bb-85 png               value    hi how r u                color     UIColor brown                      You can use this code you get data  from text json file  in swift3        let filePath   Bundle main path forResource   nameoftheyourjsonTextfile   ofType   json         let contentData   FileManager default contents atPath  filePath       let content   NSString data  contentData   encoding  String Encoding utf8 rawValue  as  String      print content      let json   try  JSONSerialization jsonObject with  contentData   as  NSDictionary     print json      let app   json object forKey   Scenes   as  NSArray      let     NSDictionary     for dict in app            let colorNam    dict as AnyObject  object forKey   color   as  String         print  colors are   colorNam               let colour   UIColor hexString  colorNam              colorsArray append colour cgColor            colorsArray append colorNam  as  UIColor           let value    dict as AnyObject  object forKey   value   as  String         print  the values are   value            valuesArray append value           let images    dict as AnyObject  object forKey   image   as  String         let url   URL string  images as String          let data   try  Data contentsOf  url           print data          let image1   UIImage data  data    as UIImage         imagesArray append image1           print image1

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For my txt file works this way   let myFileURL   NSBundle mainBundle   URLForResource  listacomuni   withExtension   txt    let myText   try  String contentsOfURL  myFileURL  encoding  NSISOLatin1StringEncoding  print String myText

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Assuming that you have moved your text file data txt to your Xcode-project  Use drag n drop and check  Copy files if necessary   you can do the following just like in Objective-C   let bundle   NSBundle mainBundle   let path   bundle pathForResource  data   ofType   txt           let content   NSString stringWithContentsOfFile path  as String  println content     prints the content of data txt   Update   For reading a file from Bundle  iOS  you can use   let path   NSBundle mainBundle   pathForResource  FileName   ofType   txt   var text   String contentsOfFile  path   encoding  NSUTF8StringEncoding  error  nil   println text    Update for Swift 3   let path   Bundle main path forResource   data   ofType   txt      file path for file  data txt  var text   String contentsOfFile  path   encoding  NSUTF8StringEncoding  error  nil     For Swift 5  let path   Bundle main path forResource   ListAlertJson   ofType   txt      file path for file  data txt  let string   try String contentsOfFile  path   encoding  String Encoding utf8

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Xcode 8 3 2 Swift 3 x  Using NSKeyedArchiver and NSKeyedUnarchiver  Reading file from documents  let documentsDirectoryPathString   NSSearchPathForDirectoriesInDomains  documentDirectory   userDomainMask  true  first  let documentsDirectoryPath   NSURL string  documentsDirectoryPathString   let jsonFilePath   documentsDirectoryPath appendingPathComponent  Filename json    let fileManager   FileManager default var isDirectory  ObjCBool   false  if fileManager fileExists atPath   jsonFilePath  absoluteString    isDirectory   amp isDirectory     let finalDataDict   NSKeyedUnarchiver unarchiveObject withFile   jsonFilePath  absoluteString    as   String  Any    else       print  File does not exists       Write file to documents  NSKeyedArchiver archiveRootObject finalDataDict  toFile  jsonFilePath  absoluteString

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It is recommended to read and write files asynchronously  and it s so easy to do in pure Swift  here is the protocol  protocol FileRepository       func read from path  String  throws - gt  String     func readAsync from path  String  completion   escaping  Result lt String  Error gt   - gt  Void      func write   string  String  to path  String  throws     func writeAsync   string  String  to path  String  completion   escaping  Result lt Void  Error gt   - gt  Void     As you can see it allows you to read and write files synchronously or asynchronously  Here is my implementation in Swift 5  class DefaultFileRepository               MARK  Properties          let queue  DispatchQueue    global       let fileManager  FileManager    default     lazy var baseURL  URL             try  fileManager              url for   libraryDirectory  in   userDomainMask  appropriateFor  nil  create  true               appendingPathComponent  quot MyFiles quot                            MARK  Private functions          private func doRead from path  String  throws - gt  String           let url   baseURL appendingPathComponent path                   var isDir  ObjCBool   false         guard fileManager fileExists atPath  url path  isDirectory   amp isDir   amp  amp   isDir boolValue else               throw ReadWriteError doesNotExist                            let string  String         do               string   try String contentsOf  url            catch               throw ReadWriteError readFailed error                             return string                private func doWrite   string  String  to path  String  throws           let url   baseURL appendingPathComponent path          let folderURL   url deletingLastPathComponent                    var isFolderDir  ObjCBool   false         if fileManager fileExists atPath  folderURL path  isDirectory   amp isFolderDir                if  isFolderDir boolValue                   throw ReadWriteError canNotCreateFolder                         else               do                   try fileManager createDirectory at  folderURL  withIntermediateDirectories  true                catch                   throw ReadWriteError canNotCreateFolder                                          var isDir  ObjCBool   false         guard  fileManager fileExists atPath  url path  isDirectory   amp isDir      isDir boolValue else               throw ReadWriteError canNotCreateFile                            guard let data   string data using   utf8  else               throw ReadWriteError encodingFailed                            do               try data write to  url            catch               throw ReadWriteError writeFailed error                           extension DefaultFileRepository  FileRepository       func read from path  String  throws - gt  String           try queue sync   try self doRead from  path                   func readAsync from path  String  completion   escaping  Result lt String  Error gt   - gt  Void            queue async               do                   let result   try self doRead from  path                  completion  success result                 catch                   completion  failure error                                          func write   string  String  to path  String  throws           try queue sync   try self doWrite string  to  path                   func writeAsync   string  String  to path  String  completion   escaping  Result lt Void  Error gt   - gt  Void            queue async               do                   try self doWrite string  to  path                  completion  success Void                   catch                   completion  failure error                                          enum ReadWriteError  LocalizedError               MARK  Cases          case doesNotExist     case readFailed Error      case canNotCreateFolder     case canNotCreateFile     case encodingFailed     case writeFailed Error

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Simplest way to read a file in Swift   4 0   let path   Bundle main path forResource   data   ofType   txt      file path for file  data txt          do               var text   try String contentsOfFile  path                     catch    print  error

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The current accepted answer above from Adam had some errors for me but here is how I reworked his answer and made this work for me   let file    file txt   let dirs   String     NSSearchPathForDirectoriesInDomains NSSearchPathDirectory DocumentDirectory  NSSearchPathDomainMask AllDomainsMask  true  as   String   if  dirs    nil        let directories  String    dirs      let dirs   directories 0     documents directory     let path   dirs stringByAppendingPathComponent file       let text    some text         writing     text writeToFile path  atomically  false  encoding  NSUTF8StringEncoding  error  nil          reading      var error NSError         reading     let text2   String contentsOfFile  path  encoding NSUTF8StringEncoding  error   amp error       if let theError   error           print    theError localizedDescription

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To avoid confusion and add ease  I have created two functions for reading and writing strings to files in the documents directory   Here are the functions   func writeToDocumentsFile fileName String value String        let documentsPath   NSSearchPathForDirectoriesInDomains  DocumentDirectory   UserDomainMask  true  0  as  NSString     let path   documentsPath stringByAppendingPathComponent fileName      var error NSError      value writeToFile path  atomically  true  encoding  NSUTF8StringEncoding  error   amp error     func readFromDocumentsFile fileName String  - gt  String       let documentsPath   NSSearchPathForDirectoriesInDomains  DocumentDirectory   UserDomainMask  true  0  as  NSString     let path   documentsPath stringByAppendingPathComponent fileName      var checkValidation   NSFileManager defaultManager       var error NSError      var file String      if checkValidation fileExistsAtPath path            file   NSString contentsOfFile  path  encoding  NSUTF8StringEncoding  error  nil  as  String       else           file     ERROR    fileName  does not exist              return file     Here is an example of their use   writeToDocumentsFile  MyText txt   Hello world     let value   readFromDocumentsFile  MyText txt   println value     Would output  Hello world    let otherValue   readFromDocumentsFile  SomeText txt   println otherValue     Would output   ERROR  SomeText txt does not exist     Hope this helps   Xcode Version  6 3 2

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New simpler and recommended method  Apple recommends using URLs for filehandling and the other solutions here seem deprecated  see comments below    The following is the new simple way of reading and writing with URL s  don t forget to handle the possible URL errors    Swift 5   4 and 3 1  import Foundation     Needed for those pasting into Playground  let fileName    Test  let dir   try  FileManager default url for   documentDirectory         in   userDomainMask  appropriateFor  nil  create  true      If the directory was found  we write a file to it and read it back if let fileURL   dir  appendingPathComponent fileName  appendingPathExtension  txt             Write to the file named Test     let outString    Write this text to the file      do           try outString write to  fileURL  atomically  true  encoding   utf8        catch           print  Failed writing to URL    fileURL   Error      error localizedDescription                Then reading it back from the file     var inString          do           inString   try String contentsOf  fileURL        catch           print  Failed reading from URL    fileURL   Error      error localizedDescription            print  Read from the file    inString

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func writeToDocumentsFile fileName String value String        let documentsPath   NSSearchPathForDirectoriesInDomains  documentDirectory   userDomainMask  true  0  as NSString     let path   documentsPath appendingPathComponent fileName      do      try value write toFile  path  atomically  true  encoding  String Encoding utf8   catch               func readFromDocumentsFile fileName String  - gt  String       let documentsPath   NSSearchPathForDirectoriesInDomains  documentDirectory   userDomainMask  true  0  as NSString     let path   documentsPath appendingPathComponent fileName      let checkValidation   FileManager default     var file String      if checkValidation fileExists atPath  path            do         try file   NSString contentsOfFile  path  encoding  String Encoding utf8 rawValue  as String          catch              file                          else           file                 return file

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Xcode 8 x     Swift 3 x or later  do          get the documents folder url     if let documentDirectory   FileManager default urls for   documentDirectory  in   userDomainMask  first              create the destination url for the text file to be saved         let fileURL   documentDirectory appendingPathComponent  file txt              define the string text to be saved         let text    Hello World                 writing to disk             Note  if you set atomically to true it will overwrite the file if it exists without a warning         try text write to  fileURL  atomically  false  encoding   utf8          print  saving was successful              any posterior code goes here            reading from disk         let savedText   try String contentsOf  fileURL          print  savedText    savedText        Hello World     n          catch       print  error    error

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I had to recode like this   let path   NSBundle mainBundle   pathForResource  Output 5   ofType   xml   let text   try  NSString contentsOfFile  path  as String  encoding  NSUTF8StringEncoding  print text

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This works with Swift 3 1 1 on Linux   import Foundation  let s   try  String contentsOfFile   yo   encoding   utf8

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Swift 3 x - 5 x  The Best Example is to Create a Local Logfile with an Extension  txt that can visible and show in the  Files App  with current date and Time as a File Name  just add this code in info plist enable these two features    UIFileSharingEnabled   LSSupportsOpeningDocumentsInPlace   and this Function Below   var logfileName   String        func getTodayString   - gt  String       let date   Date       let calender   Calendar current     let components   calender dateComponents   year  month  day  hour  minute  second   from  date       let year   components year     let month   components month     let day   components day     let hour   components hour     let minute   components minute     let second   components second      let today string   String year      -    String month      -    String day      -    String hour           String minute           String second     txt       return today string     func LogCreator        logfileName   getTodayString        print  LogCreator  Logfile Generated Named    logfileName         let file   logfileName   this is the file  we will write to and read from it      let text    some text    just a text      if let dir   FileManager default urls for   documentDirectory  in   userDomainMask  first            let fileURL   dir appendingPathComponent file          let documentPath   NSSearchPathForDirectoriesInDomains  documentDirectory  userDomainMask  true  0          print  LogCreator  The Logs are Stored at location   documentPath                writing         do               try text write to  fileURL  atomically  false  encoding   utf8                    catch     error handling here                reading         do               let text2   try String contentsOf  fileURL  encoding   utf8              print  LogCreator  The Detail log are  -  text2                      catch     error handling here                  1   https   i stack imgur com 4eg12 png

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You may find this tool useful to not only read from file in Swift but also parse your input  https   github com shoumikhin StreamScanner  Just specify the file path and data delimiters like this   import StreamScanner  if let input   NSFileHandle forReadingAtPath    file path         let scanner   StreamScanner source  input  delimiters  NSCharacterSet charactersInString     n       separate data by colons and newlines      while let field  String   scanner read                   use field           Hope  this helps

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Xcode 8  Swift 3 way to read file from the app bundle   if let path   Bundle main path forResource  filename  ofType  nil        do           let text   try String contentsOfFile  path  encoding  String Encoding utf8          print text        catch           printError  Failed to read text from   filename            else       printError  Failed to load file from app bundle   filename           Here s a convenient copy and paste Extension  public extension String       func contentsOrBlank  - gt String           if let path   Bundle main path forResource self   ofType  nil                do                   let text   try String contentsOfFile path  encoding  String Encoding utf8                  return text                   catch   print  Failed to read text from bundle file   self                else   print  Failed to load file from bundle   self              return                  For example  let t    yourFile txt  contentsOrBlank     You almost always want an array of lines   let r  String     yourFile txt        contentsOrBlank         characters       split separator    n   omittingEmptySubsequences ignore        map String init

[file-io] Read and write a String from text file

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