Table 14.1 summarizes the operations that you have for launching a process.
|Operation||Standard Input||Standard Output||Standard Error||Waited for?|
|Inherited from program||Inherited from program||Inherited from program||Yes|
|Backquoted string||Inherited from program||Captured as string value||Inherited from program||Yes|
|open() command as filehandle for output||Connected to filehandle||Inherited from program||Inherited from program||Only at time of close()|
|open() command as filehandle for input||Inherited from program||Connected to filehandle||Inherited from program||Only at time of close()|
|fork, exec, wait, waitpid||User selected||User selected||User selected||User selected|
The simplest way to create a process is with the system function. Standard input, output, and error are unaffected (they're inherited from the Perl process). A backquoted string creates a process, capturing the standard output of the process as a string value for the Perl program. Standard input and standard error are unaffected. Both these methods require that the process finish before any more code is executed.
A simple way to get an asynchronous process (one that allows the Perl program to continue before the process is complete) is to open a command as a filehandle, creating a pipe for the command's standard input or standard output. A command opened as a filehandle for reading inherits the standard input and standard error from the Perl program; a command opened as ...