Programming Perl, 4th Edition

open

open FILEHANDLE, MODE, EXPR, LIST
open FILEHANDLE, MODE, EXPR
open FILEHANDLE, MODE, REFERENCE
open FILEHANDLE, EXPR

The open function associates an internal FILEHANDLE with an external file specification given by EXPR or LIST. It may be called with two or three arguments (or more if the third argument is a command). When three or more arguments are present, the second argument specifies the access MODE in which the file should be opened, and the remaining argument supplies the actual filename or the command to execute, depending on the mode. In the case of a command, additional arguments may be supplied if you wish to invoke the command directly without involving a shell, much like system or exec. Or the command may be supplied as a single argument (the third one), in which case the decision to invoke the shell depends on whether the command contains shell metacharacters. (Don’t use more than three arguments if the arguments are ordinary filenames; it won’t work.) If the MODE is not recognized, open raises an exception.

As a special case, the three-argument form with a read/write ...