In Perl how can I read an entire file into a string

Question

I m trying to open an  html file as one big long string   This is what I ve got   open FILE   index html   or die  Can t read file  filename       n      document    lt FILE gt    close  FILE     print  document    which results in     lt  DOCTYPE HTML PUBLIC  -  W3C  DTD HTML 4 01 Transitional  EN   However  I want the result to look like     lt  DOCTYPE HTML PUBLIC  -  W3C  DTD HTML 4 01 Transitional  EN   http   www w3 org TR html4 loose dtd  gt   lt html gt   lt head gt   lt meta http-equiv  Content-Type  content  text html  charset iso-8859-1  gt    This way I can search the entire document more easily

User · Answer

open f   test txt   file   join      lt f gt     lt f gt  - returns an array of lines from our file  if    has the default value   n   and then join    will stick this array into

User · Answer

Add    local       before reading from the file handle  See How can I read in an entire file all at once   or     perldoc -q  entire file   See Variables related to filehandles in perldoc perlvar and perldoc -f local   Incidentally  if you can put your script on the server  you can have all the modules you want  See How do I keep my own module library directory    In addition  Path  Class  File allows you to slurp and spew   Path  Tiny gives even more convenience methods such as slurp  slurp raw  slurp utf8 as well as their spew counterparts

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With File  Slurp   use File  Slurp  my  text   read file  index html      Yes  even you can use CPAN

User · Answer

This is more of a suggestion on how NOT to do it  I ve just had a bad time finding a bug in a rather big Perl application  Most of the modules had its own configuration files  To read the configuration files as-a-whole  I found this single line of Perl somewhere on the Internet     Bad  Don t do that  my  content   do local  ARGV      filename  lt  gt      It reassigns the line separator as explained before  But it also reassigns the STDIN   This had at least one side effect that cost me hours to find  It does not close the implicit file handle properly  since it does not call closeat all    For example  doing that   use strict  use warnings   my  filename    some-file txt    my  content   do local  ARGV      filename  lt  gt    my  content2   do local  ARGV      filename  lt  gt    my  content3   do local  ARGV      filename  lt  gt     print  After reading a file 3 times redirecting to STDIN     n    open  FILE    lt     filename  or die      print  After opening a file using dedicated file handle     n    while   lt FILE gt         print  read line     n      print  before close     n   close FILE  print  after close     n     results in   After reading a file 3 times redirecting to STDIN  3 After opening a file using dedicated file handle  3 read line  1 read line  2       read line  46 before close  46 after close  0   The strange thing is  that the line counter    is increased for every file by one  It s not reset  and it does not contain the number of lines  And it is not reset to zero when opening another file until at least one line is read  In my case  I was doing something like this   while     lt   skipLines    lt FILE gt      Because of this problem  the condition was false because the line counter was not reset properly  I don t know if this is a bug or simply wrong code    Also calling close  oder close STDIN  does not help   I replaced this unreadable code by using open  string concatenation and close  However  the solution posted by Brad Gilbert also works since it uses an explicit file handle instead   The three lines at the beginning can be replaced by   my  content   do local     open my  f1    lt     filename  or die     my  tmp1    lt  f1 gt   close  f1 or die      tmp1   my  content2   do local     open my  f2    lt     filename  or die     my  tmp2    lt  f2 gt   close  f2 or die      tmp2   my  content3   do local     open my  f3    lt     filename  or die     my  tmp3    lt  f3 gt   close  f3 or die      tmp3     which properly closes the file handle

User · Answer

Use        undef    before  document    lt FILE gt       is the input record separator  which is a newline by default  By redefining it to undef  you are saying there is no field separator  This is called  slurp  mode   Other solutions like undef    and local     but not my     redeclare    and thus produce the same effect

User · Answer

I don t know if it s good practice  but I used to use this     a  lt F gt

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I would do it like this   my  file    index html   my  document   do       local      undef      open my  fh    lt     file         or die  could not open  file            lt  fh gt        Note the use of the three-argument version of open  It is much safer than the old two-  or one-  argument versions  Also note the use of a lexical filehandle  Lexical filehandles are nicer than the old bareword variants  for many reasons  We are taking advantage of one of them here  they close when they go out of scope

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These are all good answers   BUT if you re feeling lazy  and the file isn t that big  and security is not an issue  you know you don t have a tainted filename   then you can shell out    x  cat  tmp foo        note backticks  qw cat      also works

User · Answer

A simple way is   while   lt FILE gt      document           Another way is to change the input record separator       You can do it locally in a bare block to avoid changing the global record separator         open F   filename        local      undef       d    lt F gt

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You could simply create a sub-routine    Get File Contents sub gfc       open FC     0       join      lt FC gt

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You re only getting the first line from the diamond operator  lt FILE gt  because you re evaluating it in scalar context    document    lt FILE gt      In list array context  the diamond operator will return all the lines of the file     lines    lt FILE gt   print  lines

User · Answer

Either set    to undef  see jrockway s answer  or just concatenate all the file s lines    content   join      lt  fh gt      It s recommended to use scalars for filehandles on any Perl version that supports it

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I would do it in the simplest way  so anyone can understand what happens  even if there are smarter ways   my  text       while  my  line    lt FILE gt          text     line

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Another possible way   open my  fh    lt     filename   read  fh  my  string  -s  fh  close  fh

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All the posts are slightly non-idiomatic   The idiom is   open my  fh    lt     filename or die  error opening  filename       my  data   do   local      lt  fh gt       Mostly  there is no need to set    to undef

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From perlfaq5  How can I read in an entire file all at once      You can use the File  Slurp module to do it in one step   use File  Slurp    all of it   read file  filename     entire file in scalar  all lines   read file  filename     one line per element   The customary Perl approach for processing all the lines in a file is to do so one line at a time   open  INPUT   file         die  can t open  file       while   lt INPUT gt         chomp        do something with          close INPUT                die  can t close  file         This is tremendously more efficient than reading the entire file into memory as an array of lines and then processing it one element at a time  which is often--if not almost always--the wrong approach  Whenever you see someone do this    lines    lt INPUT gt     you should think long and hard about why you need everything loaded at once  It s just not a scalable solution  You might also find it more fun to use the standard Tie  File module  or the DB File module s  DB RECNO bindings  which allow you to tie an array to a file so that accessing an element the array actually accesses the corresponding line in the file   You can read the entire filehandle contents into a scalar     local  INPUT       open  INPUT   file         die  can t open  file        var    lt INPUT gt       That temporarily undefs your record separator  and will automatically close the file at block exit  If the file is already open  just use this    var   do   local      lt INPUT gt       For ordinary files you can also use the read function   read  INPUT   var  -s INPUT      The third argument tests the byte size of the data on the INPUT filehandle and reads that many bytes into the buffer  var

[string] In Perl, how can I read an entire file into a string?

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