How can I extract and save text using Perl?

No extracted data output to data2.txt? What goes wrong to the code?

MyFile.txt

ex1,fx2,xx1
mm1,nn2,gg3
EX1,hh2,ff7

This is my desired output in data2.txt:

ex1,fx2,xx1
EX1,hh2,ff7

#! /DATA/PLUG/pvelasco/Softwares/PERLINUX/bin/perl -w

my $infile  ='My1.txt';
my $outfile ='data2.txt';

open IN,  '<', $infile  or die "Cant open $infile:$!";
open OUT, '>', $outfile or die "Cant open $outfile:$!";

while (<IN>) {   
  if (m/EX$HF|ex$HF/) {
    print OUT $_, "\n";      
    print $_;   
  }
}

close IN;
close OUT;

From stackoverflow Shiel

• When I run your code, but name the input file My1.txt instead of MyFile.txt I get the desired output - except with empty lines, which you can remove by removing the , "\n" from the print statement.

  Shiel : Oh sorry I forgot to edit My1.txt. It should be MyFile.txt.
  From moritz

• This regex makes no sense:

  m/EX$HF|ex$HF/
  

  Is $HF supposed to be a variable? What are you trying to match?

  Also, the second line in every Perl script you write should be:

  use strict;
  

  It will make Perl catch such mistakes and tell you about them, rather than silently ignoring them.

  Brad Gilbert : ... and the third should be `use warnings`.

  raldi : He already has -w on the first line.

  Brad Gilbert : Well why doesn't he just add -Mstrict to the first line?
  From raldi

• while (<IN>) {
    if (m/^(EX|ex)\d.*/) {   
      print OUT "$_";      
      print $_;   
    }
  }
  

  Jouni K. Seppänen : Also, if you don't need the (debug?) output of all lines in the input file, you can reduce this to the one-liner perl -ne 'print if /^(EX|ex)\d/'

  John Ferguson : perl golf has its place, but I'd rather people put readable code into production.

  Brad Gilbert : This *is* simple enough to use a one-liner.
  From benPearce

• Bleh! "use strict;" "use warnings;". Lexical-filehandles. Three-args-open.

  From Shlomi Fish

• What are you trying to do? Keep all the lines that start with EX? Using a regexp is overkill - you're much better off just checking the first two letters. In python:

  
  
  from __future__ import with_statement
  class converter(object):
      def __init__(self, inFile, outFile):
          self.inFile, self.outFile = inFile, outFile
  
  def main(self):
      with open(self.inFile, 'r') as infsock:
          with open(self.outFile, 'w') as outfsock:
              for line in infsock:
                  self.doReplace(line, outfsock)
  
  def doReplace(self, line, outsock):
      if ''.join(line[:2]).upper() == "EX":
          outsock.write(line)
  
  
  if name == 'main':
      import sys
      ZeConverter = converter(sys.argv[1], sys.argv[2])
      ZeConverter.main()
  

  Sub out doReplace if you need a different replacement method

  From kanja

• The filenames don't match.

  open(my $inhandle, '<', $infile)   or die "Cant open $infile: $!";
  open(my $outhandle, '>', $outfile) or die "Cant open $outfile: $!";
  
  while(my $line = <$inhandle>) {   
  
      # Assumes that ex, Ex, eX, EX all are valid first characters
      if($line =~ m{^ex}i) {         # or   if(lc(substr $line, 0 => 2) eq 'ex') {
          print { $outhandle } $line;      
          print $line;
      }
  }
  

  And yes, always always use strict;

  You could also chomp $line and (if using perl 5.10) say $line instead of print "$line\n".

  raldi : What are the braces for in this line? print { $outhandle } $line;

  draegtun : It helps avoid mistakes like... print $outhandle, $line; (the comma means print won't recognise $outhandle as a file handle). Its a recommendation from "Perl Best Practises" by Damian Conway.

  Brad Gilbert : I didn't realize that would work.
  From Berserk

• Sorry if this seems like stating the bleeding obvious, but what's wrong with

  grep -i ^ex < My1.txt > data2.txt
  

  ... or if you really want to do it in perl (and there's nothing wrong with that):

  perl -ne '/^ex/i && print' < My1.txt > data2.txt
  

  This assumes the purpose of the request is to find lines that start with EX, with case-insensitivity.

  From RET