It is always good to make sure the file you are opening opens. Because if it doesn't the program will just keep running with no errors and you will not get your desired results. The easiest way to do this is.

open (FILE, "file") || die "file could not be opened";
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$file = "some_file.txt"; 
open(FILE,"$file") or &Error($!);
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sub Error {
        $error = shift or $error = "unknown";
        print "Sorry, but there was an error.  Could not open $file";
        print "Error:  $error";
        &End;
}
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close FILE or die "Could not close $file";
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LeGo

open(file, ">$filename")
flock file, 2;
print file "Whatever you want to say";
close(file);
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It doesn't do much good to flock a file that you've already erased. Perhaps you are mixing things from different stuff you've seen in some sort of "opcode soup" that you hope will taste good once you're done.

To me, it's bad from the first taste. :)

-- Randal L. Schwartz, Perl hacker

of course it will create a new file. since you have opened it in write mode..it will open a new file and write data into it. if the file had already existed it would have removed the whole existing data and just put in data you just wrote. to prevent this open in >> mode

It occurs to me that this fact might not be intuitively obvious to someone that isn't already used to that behavior, as for instance from regular use of bash. It's intuitively obvious to me, but I'm a penguinista. Those who write Perl but use Windows, for instance, wouldn't be used to that kind of behavior. Remember that in the Windows GUI environment files never get named until they're saved after editing. Habitual Windows users probably never realize that what's going on is that the file is actually only being "opened" for the first time when that "okay" button in the save dialog is clicked.

So: For those of us used to that sort of behavior (like 'nix users), it's "Of course it will create a new file." For those who are not (like Windows users), it's "Oh. That's news to me."

The fact that one must use >> instead of > to edit an already extant file without wiping out its contents is an important fact, though, and it's a good thing you brought it up. It should really be included in the text of the tutorial itself.


- apotheon

CopyWrite Chad Perrin

root just forgot that you don't need to escape less-than and greater-than signs inside <CODE> tags. Obviously, it should read:

while(<FILE>)
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open(file, ">$filename")
flock file, 2;
print file "Whatever you want to say";
close(file);
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No, before you can help yourself. Try Linux or FreeBSD or OpenBSD instead of Redmond crap. Now serious. try:

#!/usr/bin/perl

open(OUTPUT,">>/tmp/file");

$a = "some text...";

print OUTPUT $a;


Now, change the /tmp/file and stuff to anything you want to.
HTH

vfs ("The Perl Monkey") :)

I forgot this:

it 's better to assign a variable to a filename, as:

$b = "/tmp/file";

Then change the filename in open to the name of that variable.

Cheers.

vfs.

Im having the same problem w/ writing to a file, using Win2k/ActivePerl Thinking that win2k is not handling the opening of files correctly. Please, without saying, dont use win2k, can someone post a work around? I updated w/ the suggestion you posted as such:

#!perl -w

open(FILE, "data.txt");          #opens data.txt in read-mode
while(<FILE>){                   #reads line by line from FILE which i
+s the filehandle for data.txt
   chomp;
   print "Saw $_ in data.txt\n"; #shows you what we have read
}
close FILE;                      #close the file.
$a = "keylogger.dat";
open FILE, ">$a" or die;  #opens file to be written to
while(<>){                    #while we're getting input from the keyb
+oard
   print FILE $_;             #write it to our file
}
close FILE;                   #then close our file.
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"Re: File Input and Output by gpoduval on Jan 30, 2001 at 06:42 hmm...when i tried the >>filename nothing got appended into the file. it remained as it is i am using activestate activeperl for windows on win2k. i suspect this might be because i dont know how to end a program. anybody can help me ? www.comp.nus.edu.sg/~gokulpod"

I believe you need work in a directory like that, c:\test. It happened to me same you, because I´ve worked in a directory like this x:\test. Luiyi, luiyi2manu@gmail.com

getc. Note well the documentation -- it's still buffered input!

ObSampleCode:

while ($_ = getc STDIN) {
  $_ = ord $_;
  printf "%02x %c\n", $_, 32 <= $_ && $_ < 127 ? $_ : ord '?';
}
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Hi, I have just started working on PERL and am facing this problem. Is the implementation done like this? i have a text file sample.txt which has 3 lines abc deg hij when i read everything once i get all the details and then am not able 2 read it again. code used is open(file1,"sample.txt"); print(<file1>); $line1=<file>; print($line1); This does not print anything. Can u pls suggest?Have I done some mistake? Thanks KP

#!/usr/bin/perl -w

#open(IN, "input.txt");
open(OUT, ">out.txt");

while( <STDIN>)
{
        print $_;
        print OUT $_;
}

#close (IN);
close (OUT);
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try this.

#!/usr/bin/perl -w

use strict;

my $output_file = "out.txt";
my $user_input = "";
my $quit_code = "quit\n";

open(OUTPUT, ">$output_file) ||
   die "Unable to open $output_file for writing: $!\n";

while ($user_input ne $quit_code)
{
   print "Enter some text: ";
   $user_input = <STDIN>;
   print OUTPUT $user_input;
}

close(OUTPUT) ||
   die "Unable to close $output_file: $!\n;
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fred
20.4
harv
5.6
tony
5.13
dennis
401.1
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open(FILE, "input.dat");

@list;
while(<FILE>) {
    chomp;
    push @list, $_;
}

$i="harv";
$loc=-1;

$cnt=0;
foreach $list(@list) {
    if($i eq $list) {
        print "YES!\n";
    }
}
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Edit kudra, 2001-07-25 Changed title

mmhhh, different possibilites that this doesn't work

• try if this works:

  use strict;
  use warnings;
  
  my @list;
  
  while(<DATA>) {
      chomp;
      push @list, $_;
  }
  
  my $i="harv";
  
  foreach my $list (@list) {
      if($i eq $list) {
          print "YES!\n";
      }
  }
  
  __DATA__
  fred
  20.4
  harv
  5.6
  tony
  5.13
  dennis
  401.1
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  The DATA section behaves exactly like a file - inside your file and you don't have to open it. If it does then
• check if your file opened correctly (and specify the opening mode): open (FILE, "<", "input.dat") or die "Couldn't open input.dat: $!"; The die will abort the program if 'input.dat' couldn't be opened. The $! variable contains an error message and is set automatically if an error during the open occured.
• You should use strict; and use warnings; (equivalent to perl -w). It protects you from typing mistakes - there aren't any in your example, this is more general advice. And it shows useful warnings if you do some possibly 'stupid' things.

-- Hofmator

I recently had a similar problem. The error is in your comparison ($i eq $list). Then the loop gets to the point that you are expecting a "Yes", the values of your variables are $i="harv" $list="harv\n" I solved my problem by changing $i to include the carriage return. You could also solve this problem by using pattern matching rather than a straight comparison, or by chopping off the last character of the input lines.

It looked like he was chomping in his code. He was chomping the list as he added each element to the array. That should take care of the carriage return that you are referring to.

Trailing space after "harv" in your input file? Or perhaps a carriage return and you are on Unix?

        - tye (but my friends call me "Tye")

This works:

@list = qw(
        fred
        20.4
        harv
        5.6
        tony
        5.13
        dennis
        401.1
        );

$i="harv";

foreach $list(@list) {
    if($i eq $list) {
        print "YES!\n";
    }
}
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Suggest you add open (FILE, "input.dat") or die "Oops can't open input.dat Perl says $!\n"; which will *probably* tell you that perl cna't find your file. Also you don't need to push your data into an array as you do but that is by the by.

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

itś working with ctrl+d

I m having trouble using this in a script. I have a test file that looks like :

open(my $fh1, ">>", "outputcontrol.txt");
open(my $fh2, ">>", "outputoutput.txt");

while ( <> ) {
   
    my $count = ($_ =~ y/x//);
    print  "$count \n";
    # print $_;
    
    if ( $count != $delim_amnt_per_line )
    {
        print fh1 $_;
    }
    

    my ($prefix) = substr $_, 0, 7;
    next if $seen{$prefix}++;

    print fh2 $_;
}
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Its supposed to do some checks on delimiter per line and remove duplicates based on a substring, my problem is that i have zero output on the filehandles. Whereas if i ran it with just print it would print normally, both expected outputs on STDOUT. Can someone help me?

You replied to a node from 2007, its author was last here 1 year ago.

Nevertheless, when using lexical filehandles (i.e. open my $fh1, the dollar sign isn't optional. Fix:

print $fh2 $_;
#     ^
#     |
#    Here.
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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Please see Perl - Remove duplicate based on substring and check on delimiters for a more complete question (and from a registered user!), and some good answers.

---

Give a man a fish:  <%-{-{-{-<