How do you check if a file is open using Perl?

Question

Given the name of a file, how can I determine if the file is currently opened or in-use? (I am talking about files rather than Perl file handles.)

Please note that I am looking for a general-purpose Perl solution rather than an operating system-specific one. At a minimum, I would like something that works both on Windows and GNU/Linux-based systems.

Answer 1

POSIX does not provide any way to do this. Therefore, no portable solution is possible given the current portable O/S interface available.

You’d have to craft some higher level approach that provides a single point of access for the opening bits. It’s like with lock files.

Answer 2

See the following snippet (only Linux/Unix, you don't tell us which OS you run):

In a one-liner :

perl -e 'my $file = $ARGV[0]; print "file $file is opened" if `lsof $file`;' FILE

In a script :

#!/usr/bin/env perl -w

use strict;

my $file = $ARGV[0];
print "file $file is opened\n" if `lsof $file`;

To run it :

./script.pl FILENAME

Answer 3

Try Scalar::Util

The Scalar::Util module provides the openhandle() function for this. Unlike fileno(), it handles perl filehandles which aren't associated with OS filehandles. Unlike tell(), it doesn't produce warnings when used on an unopened filehandle From the module's documentation:

openhandle FH

Returns FH if FH may be used as a filehandle and is open, or FH is a tied handle. Otherwise "undef" is returned.

   $fh = openhandle(*STDIN);           # \*STDIN
   $fh = openhandle(\*STDIN);          # \*STDIN
   $fh = openhandle(*NOTOPEN);         # undef
   $fh = openhandle("scalar");         # undef

Answer 4

Try this

use strict;
open(IN, ">test");
print IN "Hello";
close(IN);
if(fileno(IN) == undef )
{
    print "File is CLOSED\n";
}

Answer 5

I know it has been a while but for Windows I have had some pretty good luck detecting a file is being written to by trying to lock the file (nothing fancy - just open for read, use Perl internal flock and close the file). this seems to work even on network files. I am not so sure if this works for Linux (it might on a write) and I do not know if it can detect other file readers.

Answer 6

I read tons of post but didn't find the solution I was looking for. In my case I have a for loop creating and closing tons of files. I wanted to check if my file handler that I created was open or not. This is how you do it

use IO::Handle;

if (something matches create a file)
{
  open( $signoff_report_html, '>', "$val21");
}
elsif ( ... )
{
  #keep doing amazing stuff
}
else
{
   if ($signoff_report_html->opened()) 
   {    
      #file is ok
      print "File is opened and ready\n";       
  }
  else 
  {
      print "File was closed ... ";
  }
}

Answer 7

Try to rename the file, will fail if it is open.

Answer 8

I realize you don't want to open the file handle, but it is probably the simplest method IMO:

open my $myfh, '<', $my_file or die "Couldn't open $my_file: $!";