Differences

This shows you the differences between two versions of the page.

--- ower_own_perl_wiki [2007/09/25 21:43] – roumani
+++ ower_own_perl_wiki [2008/01/31 21:29] (current) – typo fix cs243050
@@ Line 1: / Line 1: @@
 ====== Our Own Perl Wiki ======
 ===== Differences from Java =====
-  * Type: Variables are either **scalars** prefixed by **$**; **arrays** of scalars prefixed by **@**; or **hashes** of scalar pairs prefixed by **%**.
+  * Type: Variables are either **scalars** prefixed by **$**, **arrays** of scalars prefixed by **@**, or **hashes** of scalar pairs prefixed by **%**.
-  * Operators: same as Java except **eq**, **gt**, ... for strings.
+  * Operators: same as Java except **eq**, **gt**, **lt**, ... for string comparisons.
-  * Control Structures (selection and iteration): same plus **foreach** for hashes.
+  * 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    |