Summary of Process Operations
Table 14.1 summarizes the operations that you have for launching a process.
| 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
| Not implemented | Not implemented | Not implemented | Not implemented |
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 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 a filehandle for writing inherits the standard output and standard error from the Perl program.