#include <SD.h>

void setup()
{
  Serial.begin( 115200 );
  SD.begin( 10 );

  // Write lines to file
  File file = SD.open( "data.txt", FILE_WRITE );

  if ( file )
  {
    file.print( "\n1234" );
    file.print( "\n567" );
    file.print( "\n89" );
    file.close();
  }

  // Read all lines from file
  file = SD.open( "data.txt" );

  if ( file )
  {
    while ( file.available() )
    {
      static char line[10];
      static size_t line_index = 0;
      
      char character = file.read();

      if ( line_index < sizeof( line ) - 1 && character != '\n' )
      {
        line[ line_index++ ] = character;
      }

      if ( line_index > 0 && ( character == '\n' || !file.available() ) )
      {
        line[ line_index ] = '\0';
        line_index = 0;
        Serial.print( "\"" );
        Serial.print( line );
        Serial.println( "\"" );
      }
    }
    file.close();
  }
}

void loop()
{
}