[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 {} whoami {} subst $::tcl_platform(user)
 # raises cryptic error message when called with args, hence:
 proc whoami {} {set ::tcl_platform(user)} 

 interp alias {} -r   {} file readable
 interp alias {} -w   {} file writable
 interp alias {} -x   {} file executable
Note 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 ''test''s 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 } ...
----
This fills most of the shell special variables:
 # Create some shellish variables:
 proc sh'specials {} {
    global argv
    set ::0   $::argv0
    set n 0
    foreach i $argv {
	set t [lindex $argv $n]
	set ::[incr n] $t
    }
    set ::# [llength $argv]
    set ::\$ [pid]
    set ::? 0 ;# exit status of last command
 }
The following emulates the behavior that errors are not propagated, but may be detected from the special $? variable:
 proc ! args {
    if [catch {eval exec $args} res] {
	if {[lindex $::errorCode 0]=="CHILDSTATUS"} {
	    set ::? [lindex $::errorCode 2]
	}
    }
    set res
 }
 proc !! args {puts $args;eval ! args}

----
[Tcl and other languages] - [Arts and crafts of Tcl-Tk programming]