10.2 Opening Filehandles
Filehandles are opened using the "open" operator. When specifying a name for your filehandle the recommended syntax is to use all uppercase letters. The reason for this is to ensure that you don't inadvertently use a filehandle name that may one day become a reserved word in a future release of Perl. Whilst you don.t have to follow this convention it is wise to do so to maintain forward compatibility with future releases of Perl. It is also a convention that will make your code more readable to other Perl developers.
The syntax for the open operator is straightforward:
open FILEHANDLENAME "filename";
where FILEHANDLENAME is your choice of name for the filehandle and .filename. is the name of the file you want to open to connection to. For example:
open MYDATA, "datafile";
will create a filehandle called MYDATA assigned to the file on my filesystem called .datafile. The default is to open files for input. You can specifically specify that the filehandle is for input by specifying the "<" character in the file name - for example "<datafile".
To open a file for output prefix the filename with the "<" character. Note that this will create a new file if it does not already exist and overwrite if it does:
open OUTDATA, "<datafile";
If your intention is to append data onto the end of an existing data file then prefix the filename with "<<" characters. If the file already exists the original content will be preserved and new data added to the end of the file:
open APPENDDATA, "<<datafile";