Re: Redirect file output into variables

From: Michael Schlenker (schlenk_at_uni-oldenburg.de)
Date: 10/22/03 

Date: Wed, 22 Oct 2003 20:29:41 +0200

Markus Elfring wrote:

>>Can you explain more? Opening files and redirecting their
>>contents to variables, lists, or arrays is done all the time
>>by Tcl programmers. Same is true for writing vars, etc. to
>>files. Or do you mean something else?
>
>
> Did you read my first request for this topic?
>
> I am thinking about the following application.
> A limited execution environment will be created that forbids to
> directly use standard file channels. For example, I must avoid that
> output is written to STDOUT by calls to the TCL function "puts" before
> the own data processing is finished. But these calls need a place to
> store the output.
> - How can the data be stored or redirected to a temporary file?
> or
> - All file system calls will be intercepted to store the data into a
> buffer that can be copied to a variable later.

Hmm, i would use a safe interpreter for that..., as you say limited
execution environment...

proc buffered_puts {args} {
     global buffer
     switch -exact [llength $args] {
             0 { # handle error
        1 {
          append buffer(stdout) "[lindex $args 0]\n"
          }
        2 {
          if {[lindex $args 0] eq "-nonewline"} {
                append buffer(stdout) "[lindex $args 1]"
          } else {
                # check for error
                append buffer([lindex $args 0]) "[lindex $args 1]\n"
           }
          }
        3 {
          if {[lindex $args 0] eq "-nonewline"} {
                # check error
                append buffer([lindex $args 1]) "[lindex $args 2]"
          } else {
                # check for error
                append buffer([lindex $args 1]) "[lindex $args 2]\n"
           }
          }
        
        default {
                # handle error
        }
    }
}

interp create safe foo
interp alias foo puts {} buffered_puts
# do similar things with read, gets etc.

set script "script you want to execute in a safe environment"
foo eval $script

# print the buffered output

Michael Schlenker

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