Terminating the current process and replacing it with another

chain

Terminate the current process and replace it with another

SYNTAX

chain text_expression


Calling a new shell
Using the chain command under Windows

The chain command terminates the current program and replaces it with the process indicated by text_expression. When the new process terminates, control is returned to the parent of the current process.

text_expression

The name of the new process. It may be a text constant, an alphanumeric field, or a concatenation of several such items. It should form the name of the program to be called, together with any arguments required by that program.

Calling a new shell

The chain command does not call a new shell to process the program specified by text_expression. It merely replaces the current process in memory. However, if the command line represented by text_expression contains certain features, then a new shell must be called. These features are:

1

I/O redirection

2

Pipes

3

Shell expansion

If any of these is required, the new shell or command processor must be explicitly chained, with the command to be executed passed to it as a parameter.

Using the chain command under Windows

There are two ways to use the chain command under Windows:

1 chain “program args…”

Creates a DOS shell and executes the program as a DOS command. The parent program then exits.

2 chain “-program args…”

Creates a new Windows program, The parent program starts the child program and then exits.

NOTES

  • The execute() function executes a child process and returns a handle to it.

  • The exec command is used to call another program as a child task, with control returning to the current program when the child task terminates.

  • The length of the command to be executed must not exceed operating system limits. On MS-DOS, the maximum length is 128 characters.

EXAMPLE

  1. Chain a screen form program with an argument

    chain "sagewc orders " + tmp.Number

  2. Call a new shell, as redirection required

    chain "sh -c srepwc calc pterm >/dev/tty"
chain "command /c dir >dir.out"

RELATED TOPICS

exec

execute()