Learning Perl, Second Edition

14.5. Summary of Process Operations

Table 14.1 summarizes the operations that you have for launching a process.

Table 14.1. Summary of Subprocess Operations

Operation	Standard Input	Standard Output	Standard Error	Waited for?
system()	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 ...