Reference: flock
Author: Ellen Siever, Stephen Spainhour & Nathan Patwardhan
Date: 1999-07-02T01:35:05Z

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| Chapter 5 Function Reference |

## flock

    flock filehandle, operation

Establishes or removes a lock on a file opened with filehandle. This function calls one of the Unix functions `flock`, `lockf`, or the locking capabilities of `fcntl`, whichever your system supports. If none of these functions exist on your system, `flock` will produce a fatal error.

operation is the type of locking function to perform. The number by each operation name is the argument that Perl's `flock` takes by default. You may also use the operation names if you explicitly import them from the Fcntl module with `use Fcntl ":flock"`.

`LOCK_SH` (1)

  Establishes a shared lock on the file (read lock).

`LOCK_EX` (2)

  Establishes an exclusive lock on the file (write lock).

`LOCK_UN` (8)

  Removes a lock from the file.

`LOCK_NB` (4)

  Prevents `flock` from blocking while trying to establish a lock with `LOCK_SH` or `LOCK_EX` and instructs it to return immediately. `LOCK_NB` must be ored with the other operation as an expression for the operation argument, i.e., `(LOCK_EX | LOCK_NB)`.

Reference: fileno |  | Reference: fork