Richard Suchenwirth will have to exercise Tcl with colleagues who are familiar with the Bourne shell (/bin/sh - see Tcl heritage for the influences it had on Tcl!), and one task will be to prelace /bin/sh scripts with equivalent Tcl scripts.
To make this migration easier, I am planning to introduce some syntactic sugar (Salt and sugar), so familiar built-ins can still be used. Most simply with interp alias:
interp alias {} echo {} puts stdout
interp alias {} read {} gets stdin ;# if we don't need the real [read]
interp alias {} -r {} file readable
interp alias {} -w {} file writable
interp alias {} -x {} file executableNote however that echo's output cannot be redirected to a file, or through a pipe. Things like
foo=`echo $bar | grep "^grill"`
would have to be restructured:
set foo [exec grep ^grill <<$bar]
which also has its charms, but needs habituation. (On the other hand, a Tcl'er would prefer regexp anyway...)
Another difference is the exit status - if grep can't find a thing, it still raises no direct error in /bin/sh, but you can check the exit status with the special variable $? afterwards.
The following one-liner emulates a frequently used part of /bin/sh's test command:
proc -f name {expr {[file exists $name] && [file type $name]=="file"}}This way, /bin/sh code written like this:
if [ -f $filename ] ...
needs no rewriting - but be aware that this is not a complete emulation of tests switches, so
if [ $# -ne 1 ] ...
would have to rewritten in expr syntax (braced condition, C operators), but we even emulate the Perlish special variable ?# :
set # [llength $argv]
if {${#} != 1 } ...Tcl and other languages - Arts and crafts of Tcl-Tk programming