The correct way to read a data file into an array

Question

I have a data file  with each line having one number  like  10 20 30 40   How do I read this file and store the data into an array    So that I can conduct some operations on this array

User · Answer

Tie  File is what you need      Synopsis    This file documents Tie  File version 0 98 use Tie  File   tie  array   Tie  File    filename  or die        array 13     blah         line 13 of the file is now  blah  print  array 42            display line 42 of the file   n recs    array           how many records are in the file    array -  2               chop two records off the end   for   array      s PERL Perl g            Replace PERL with Perl everywhere in the file      These are just like regular push  pop  unshift  shift  and splice   Except that they modify the file in the way you would expect  push  array  new recs     my  r1   pop  array  unshift  array  new recs     my  r2   shift  array   old recs   splice  array  3  7  new recs      untie  array               all finished

User · Answer

open AAAA   filepath filename txt   my  array    lt AAAA gt     read the file into an array of lines close AAAA

User · Answer

It depends on the size of the file  The solutions above tend to use convenient shorthands to copy the entire file into memory  which will work in many cases   For very large files you may need to use a streaming design where read the file by line or in chucks  process the chunks  then discard them from memory    See the answer on reading line by line with perl if that s what you need

User · Answer

There is the easiest method  using File  Slurp module   use File  Slurp  my  lines   read file  filename   chomp   gt  1     will chomp   each line   If you need some validation for each line you can use grep in front of read file   For example  filter lines which contain only integers   my  lines   grep      d      read file  filename   chomp   gt  1

User · Answer

Just reading the file into an array  one line per element  is trivial   open my  handle    lt     path to file  chomp my  lines    lt  handle gt    close  handle    Now the lines of the file are in the array  lines   If you want to make sure there is error handling for open and close  do something like this  in the snipped below  we open the file in UTF-8 mode  too    my  handle  unless  open  handle    lt  encoding utf8     path to file       print STDERR  Could not open file   path to file      n        we return  undefined   we could also  die  or  croak     return undef   chomp my  lines    lt  handle gt    unless  close  handle         what does it mean if close yields an error and you are just reading     print STDERR  Don t care error while closing   path to file      n

User · Answer

I like      data    cat  var tmp somefile     It s not as glamorous as others  but  it works all the same   And      todays data     var tmp somefile    open INFILE    todays data      data    lt INFILE gt     close INFILE     Cheers

[perl] The correct way to read a data file into an array

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