How do I lock a file in Perl?

by

If you end up using flock, here’s some code to do it:

use Fcntl ':flock'; # Import LOCK_* constants

# We will use this file path in error messages and function calls.
# Don't type it out more than once in your code.  Use a variable.
my $file="/path/to/some/file";

# Open the file for appending.  Note the file path is quoted
# in the error message.  This helps debug situations where you
# have a stray space at the start or end of the path.
open(my $fh, '>>', $file) or die "Could not open '$file' - $!";

# Get exclusive lock (will block until it does)
flock($fh, LOCK_EX) or die "Could not lock '$file' - $!";

# Do something with the file here...

# Do NOT use flock() to unlock the file if you wrote to the
# file in the "do something" section above.  This could create
# a race condition.  The close() call below will unlock the
# file for you, but only after writing any buffered data.

# In a world of buffered i/o, some or all of your data may not 
# be written until close() completes.  Always, always, ALWAYS 
# check the return value of close() if you wrote to the file!
close($fh) or die "Could not write '$file' - $!";

Some useful links:

In response to your added question, I’d say either place the lock on the file or create a file that you call ‘lock’ whenever the file is locked and delete it when it is no longer locked (and then make sure your programs obey those semantics).

More Related Contents:

  1. What is the best way to slurp a file into a string in Perl?
  2. What’s the best way to open and read a file in Perl?
  3. How do I change, delete, or insert a line in a file, or append to the beginning of a file in Perl?
  4. What’s the difference between iterating over a file with foreach or while in Perl?
  5. In Perl, how do I change, delete, or insert a line in a file, or append to the beginning of a file?
  6. Failing to install MIME::Base64 using cpan [closed]
  7. Declaring a 2D coordinate in Perl / C / C++ [closed]
  8. Why can’t Perl find my file that is in ClearCase?
  9. Difference of Two Arrays Using Perl
  10. How can I output UTF-8 from Perl?
  11. What is the best way to open a file for exclusive access in Python?
  12. What’s the difference between a hash and hash reference in Perl?
  13. Multiline search replace with Perl
  14. How do I “use” a Perl module in a directory not in @INC?
  15. How can I process options using Perl in -n or -p mode?
  16. Powershell: Check if a file is locked
  17. How can I dynamically include Perl modules without using eval?
  18. What’s the least invasive way to read a locked file in C# (perhaps in unsafe mode)?
  19. Why do my Perl tests fail with use encoding ‘utf8’?
  20. How can I compile my Perl script so it can be executed on systems without ‘perl’ installed?
  21. How can I guess the encoding of a string in Perl?
  22. Using output from a previous job in a new one in a GitHub Action
  23. What does !! (double exclamation point) mean?
  24. Using my with parentheses and only one variable
  25. Obtain a switch/case behaviour in Perl 5
  26. How do I extract the domain out of an URL?
  27. Why does $foo->{bar} autovivify but %$foo doesn’t?
  28. How can I extract text from a PDF file in Perl?
  29. How do I retrieve the terminal width in Perl?
  30. In Perl, is it appropriate to use map in void context instead of a foreach loop?

Leave a Comment