Usage example

This section contains examples using the UNIXProcess class. Evaluate each of the expressions by highlighting them and selecting Display from the Edit menu.

One common use for a UNIXProcess is to invoke shell commands from within Smalltalk and capture the output.

"Display on the Transcript the result of a shell command."

Transcript show: (UNIXProcess shell: 'ls -al')

To invoke a command and not capture the output, the system message is used.

"Perform a shell command and direct output to the start up terminal"

UNIXProcess system: 'env'

In some situations the shell: and system: messages do not provide sufficient control over the process. The following example shows the three stages of a UNIXProcess: creation, the reading and writing of data, and termination.

"Connect user defined streams to the UNIX process stdin, stdout

and stderr."

| process output input result |

process := UNIXProcess "Create the process."

execute: 'cat'

input: true

output: true

error: nil

environment: UNIXEnvironment current.

input := process stdin.

output := process stdout.

input

nextPutAll: 'This is input sent into standard in';

close.

process waitForCompletion. "Wait for process to terminate."

output contents

Using the stream interface, it is possible to interact with a process. Future input to the process can be determined by the currently available output or state of the process.

"It is not necessary to provide all input immediately."

| process output input result |

process := UNIXProcess "Create the process."

execute: 'cat'

input: true

output: true

error: nil

environment: UNIXEnvironment current.

input := process stdin.

output := process stdout.

input

nextPutAll: 'This'; "Perform read/writes of data."

flush.

process isComplete ifTrue: [self error: 'Process should not be complete'].

input

nextPutAll: ' is input sent into standard in';

close.

process waitForCompletion. "Wait for process to terminate."

output contents

The following code is an example method for an application. The method makes use of the UNIXProcess class to mail a message to a collection of recipients with a given subject. A method similar to this could be used to interface to the UNIX mail facilities from within Smalltalk.

Note:

Highlighting the following example code and selecting Display will not work. It is a method and requires parameters.

"Send mail and ignore the reply."

mail2: recips subject: subject msg: string

| process args env |

args:= '/usr/ucb/mail'.

recips do: :person | args := args, ' ', person].

env := UNIXEnvironment current.

process := UNIXProcess

execute: args

input: true

output: true

error: nil

environment: env.

process stdin

nextPutAll: 's ',subject; cr;

nextPutAll: string; cr;

close.

process waitForCompletion.

^process exitCode