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SHELL
Syntax

    [ Process = ] SHELL Command [ WAIT ] [ FOR { { READ | INPUT } | { WRITE | OUTPUT } } ] [ AS Name ]

    SHELL Command TO Variable

Executes a command. An internal Process object is created to manage the command.

The command is a string containing a command passed to the system shell (`/bin/sh`).

- If `WAIT` is specified, then the interpreter waits for the command ending. Otherwise, the command is executed in background.

- If `FOR` is specified, then the command input-outputs are redirected so that your program intercepts them:

  - If `WRITE` is specified, you can send data to the command standard input by using the Process object with common output instructions: PRINT, WRITE, ... Note that you need a reference to the Process object for that.

  - If `READ` is specified, then events will be generated each time the command sends data to its standard output streams: the event Read is raised when data are sent to the standard output stream, and the event Error is raised when data are sent to the standard error stream. Use the process object with Stream & Input/Output functions to read the process standard output:.

If you use the `INPUT` and `OUTPUT` keywords instead of `READ` and `WRITE`, then the process is executed inside a virtual terminal. It means that the process will think running inside a true terminal.

`Name` is the event name used by the Process object. By default, it is `"Process"`.

You can get a reference to the internal Process object created by using an assignment.

If you use the second syntax, the command is executed, the interpreter waiting for its end, and the complete command output is put in the specified string.

### Examples

    ' Get the content of a directory

    SHELL "ls -la /tmp" WAIT

    ' Same thing, but in background

    DIM Content AS String

    EXEC "ls -la /tmp" FOR READ

    ...

    PUBLIC SUB Process_Read()

      DIM sLine AS String

      READ #LAST, sLine, -256

      Content = Content & sLine
      PRINT sLine;

    END

| If you want to know how many bytes you can read in a `Process_Read` event handler, use the Lof function.

| As arguments are sent to a shell, you have to quote them, as if you type a command directly in it.
    SHELL "perl -e 'print while <>;'" FOR READ WRITE
Or you can use the Quote.Shell method to create a quoted string that won't be modified by the shell.

| Unlike the VB Shell command, which returns a process ID and relies on the programmer to make API calls to control the process, the Gambas Shell function optionally returns a Process object (if used as an assignment to a variable declared AS Process) which can be used to directly kill or otherwise control the spawned process. Additionally, the process may be run synchronously or asynchronously, in contrast to the VB equivalent.

### See also

Process Management Process Lof Quote.Shell