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--- ower_own_perl_wiki [2007/09/25 21:45] – roumani
+++ ower_own_perl_wiki [2008/01/31 21:29] (current) – typo fix cs243050
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 ====== Our Own Perl Wiki ======
@@ Line 11: / Line 13: @@
   * Control Structures (selection and iteration): same as Java plus **foreach** for hashes.
-  * Cool stuff: interpolation, here-docs, regex, and web goodies such as param and &ENV.
+  * Cool stuff: interpolation, here-docs, regex, and web goodies such as param and %ENV.
 ----
+===== File I/O in Perl =====
+**Default file handlers:**
+  * STDIN: Standard input from console
+  * STDOUT: Standard output to console
+  * STDERR: Standard error output to console
+**Opening a file**
+<code perl>
+open(FILEHANDLE, filename)
+</code>
+Where FILEHANDLE specifes the name for the file handler in which you will refer to your file and filename specifies the location of your file.
+In the file name one can specify the various read/write modes.
+^ Example      ^ Description       ^
+| open(FILEHANDLE, <filename)      | opens the file for reading    |
+| open(FILEHANDLE, >filename)     | opens the file for writing    |
+| open(FILEHANDLE, >>filename)     | opens the file for appending    |
+| open(FILEHANDLE, +>filename)     | opens the file for reading and writing    |
+| open(FILEHANDLE, +<filename)     | opens the file for reading and writing    |
+| open(FILEHANDLE, +>>filename)     | opens the file for reading and writing    |
+File locking for I/O is provided using the **flock()** function. It is suggested to do the lock on a seperate file to prevent race conditions.
+<code perl>
+open(LOCK, ">write.lock")
+flock(LOCK, LOCK_EX);
+open(DATA, myFile);
+#...do work with the DATA file...
+close LOCK;
+close DATA;
+</code>
+Closing the **LOCK** handler automatically unlocks the semaphore. One can also use **flock(LOCK, LOCK_UN)** to do the unlocking specifically. The flock function takes the following operation parameters:
+^ Operation      ^ Description       ^
+| LOCK_SH      | requests a shared lock for a file, will block until lock is obtained    |
+| LOCK_EX      | requests an exclusive lock for a file, will block until lock is obtained   |
+| LOCK_UN      | unlocks the previously locked file    |
+| LOCK_NB      | should be bitwise 'or'-ed with either LOCK_SH or LOCK_EX and will result in a non-blocking lock    |