TIP #137 Version 1.1: Specifying Script Encodings for [source] and tclsh

This is not necessarily the current version of this TIP.

Abstract

This TIP proposes a way to specify encoding used to read a script with source command and tclsh shell.

Rationale

Now all Tcl scripts are expected to be in the system encoding. An author of a script or a package can't specify concrete encoding to source the script or the files of package. Common practise is to assume that encoding to be superset of ASCII, and not to use non-ASCII characters in the scripts that are targeting the wide audience of potential users.

There's a way to specify UNICODE literals with \uXXXX sequences. But it's not an universal and convenient way - this sequences aren't substituted in {}-quoted strings, and they can't be edited in WYSIWYG editors without special (and hence uncommon) support.

This TIP proposes to add the -encoding option support to source command and to tclsh. Thus, package authors will be able to specify encoding of the package files in pkgIndex.tcl; and script authors will be able to specify the script encoding when calling tclsh (either in the first line beginning with #! or in the line where the exec tclsh "$0" "$@" is located).

Specification

Tclsh will allow the encoding to be specified on the command-line in two forms: the first form is -encoding name as two separate arguments, and the second is -encoding:name (a single argument.) The second form is intended for when the script begins with #! and is because Unix kernels pass extra parameters from the #! line as a single argument.

Common use of this new options will be like this:

1. In a script:

    !#/usr/bin/tclsh -encoding:utf-8
    do something...
   

   or it could be:

    #!/bin/sh
    # I wish to use tclsh \
    exec tclsh -encoding utf-8 "$0" "$@"
   

2. In a pkgIndex.tcl:

    package ifneeded pkg 1.02 [list source -encoding utf-8 \
         [file join $dir pkg.tcl]]
   

Implementation

The implementation of this TIP can be found at http://sourceforge.net/projects/tcl as Patch #742683.

Copyright

This document is placed in the public domain.

This is not necessarily the current version of this TIP.