What are all the common ways to read a file in Ruby

Question

What are all the common ways to read a file in Ruby   For instance  here is one method   fileObj   File new  fileName   r   while  line   fileObj gets    puts line  end fileObj close   I know Ruby is extremely flexible  What are the benefits drawbacks of each approach

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One simple method is to use readlines   my array   IO readlines  filename txt     Each line in the input file will be an entry in the array   The method handles opening and closing the file for you

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The easiest way if the file isn t too long is   puts File read file name    Indeed  IO read or File read automatically close the file  so there is no need to use File open with a block

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I usually do this   open path in string   amp  read    This will give you the whole text as a string object  It works only under Ruby 1 9

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An even more efficient way is streaming by asking the operating system   s kernel to open a file  then read bytes from it bit by bit  When reading a file per line in Ruby  data is taken from the file 512 bytes at a time and split up in    lines    after that   By buffering the file   s content  the number of I O calls is reduced while dividing the file in logical chunks   Example   Add this class to your app as a service object   class MyIO   def initialize filename      fd   IO sysopen filename       io   IO new fd       buffer        end    def each  amp block       buffer  lt  lt   io sysread 512  until  buffer include           line   buffer    buffer split     2       block call line      each  amp block    rescue EOFError      io close  end end   Call it and pass the  each method a block   filename      somewhere large-file-4gb txt  MyIO new filename  each  x  puts x     Read about it here in this detailed post   Ruby Magic Slurping  amp  Streaming Files By AppSignal

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Be wary of  slurping  files  That s when you read the entire file into memory at once    The problem is that it doesn t scale well  You could be developing code with a reasonably sized file  then put it into production and suddenly find you re trying to read files measuring in gigabytes  and your host is freezing up as it tries to read and allocate memory    Line-by-line I O is very fast  and almost always as effective as slurping  It s surprisingly fast actually   I like to use   IO foreach  testfile     x  print  GOT    x     or  File foreach  testfile     x  print  GOT   x     File inherits from IO  and foreach is in IO  so you can use either   I have some benchmarks showing the impact of trying to read big files via read vs  line-by-line I O at  Why is  quot slurping quot  a file not a good practice

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file content   File read  filename with extension    puts file content    http   www ruby-doc org core-1 9 3 IO html method-c-read

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You can read the file all at once   content   File readlines  file txt  content each with index  line  i  puts    i 1     line      When the file is large  or may be large  it is usually better to process it line-by-line   File foreach   file txt    do  line    puts line end   Sometimes you want access to the file handle though or control the reads yourself   File open   file txt    do  f    loop do     break if not line   f gets     puts    f lineno     line     end end   In case of binary files  you may specify a nil-separator and a block size  like so   File open  file bin    rb   do  f    loop do     break if not buf   f gets nil  80      puts buf unpack  H      end end   Finally you can do it without a block  for example when processing multiple files simultaneously  In that case the file must be explicitly closed  improved as per comment of  antinome    begin   f   File open  file txt    while line   f gets     puts line   end ensure   f close end   References  File API and the IO API

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content    cat file    I think this method is the most  uncommon  one  Maybe it is kind of tricky  but it works if cat is installed

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if the file is small  slurping   puts File read  quot filename txt quot    if the file is big  streaming   File foreach  quot filename txt quot      line  puts line

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return last n lines from your file log or  txt  path   File join Rails root   your folder   your file log    last 100 lines    tail -n 100   path

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File open  my file path    r   do  f    f each line do  line      puts line   end end   File is closed automatically at end of block   It is also possible to explicitly close file after as above  pass a block to open closes it for you    f   File open  my file path    r   f each line do  line    puts line end f close

[ruby] What are all the common ways to read a file in Ruby?

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