See instead: Pure-tcl readline2.
aspect 2013-09-18: The code on this page seems to be entirely obsoleted by the page linked above, and the content has little of value expect the Linux Console Text Editor In Pure TCL link. Any gnomes agree strongly enough to delete the page?
slebetman: Here's my first attempt at a pure-tcl implementation of readline-like capabilities. Save this into a file tclline.tcl and source it from an interactive tclsh.
The good news is that console programs like vi and links and even the Linux Console Text Editor In Pure TCL works perfectly with this.
If you are brave enough with it you can even source it from your .tclshrc file.
ak: Note that the 'exec stty ...' is unix specific. It is also the one part we cannot do in pure Tcl. It is either the exec, or a C extension (like Expect (I think Expect can do the same changes to the pty stty is able of. IIRC)). (slebetman: ak, I edited out your comment on colors since it no longer applies to the current code. Hope you don't mind. I'll edit out my comment here as well in a couple of days if nobody objects)
slebetman: Quite true ;) I guess this really should be called Unix/Linux Readline in Pure Tcl. Actually, stty is not the only dependency. This also assumes a VT100/ANSI/xterm/linux terminal. The escape sequences won't work with things like the COMSPEC shell or even Tkcon.
slebetman 10 Mar 2009: Fixed glob * substitution to not substitute in braces{}. This is so that the expand operator {*} and regexps don't need to be backslash escaped.
slebetman 14 Jul 2006: Implemented proper (not so buggy) word completion. Word completion first searches the filesystem, then falls back to tcl commands & procs and finally to (global?) variables. Implemented the alias and unalias commands. I needed them to support coloring in ls and vi (so I can do: alias ls {ls --color=auto}). Also made history persistent by saving to a .tclline_history file and implemented a .tcllinerc file. The only remaining major features that's not yet implemented are long line editing and multi-line editing.
slebetman: New version. This now properly supports long line editing. Word completion now colours hints: commands are green, variables magenta everything else not coloured. I've also implemented "universal" command substitution which substitutes not only Tcl commands and procs but also substitutes executables via exec. So now you can do things like: set x [split [cat /etc/mtab] \n]. Multi-line editing is still not implemented.
slebetman 18 Jul 2006: Finally, multi-line editing is implemented! The main loop is also now a fileevent so this should use even less CPU time. Also implemented glob substitution of * and ~ (if you need literal * or ~ on the command line they can be escaped using backslashes: \* and \~. Also fixed a bug with alias handling in unknown.
slebetman 20 Jul 2006: Tclline now uses Tclx if available to prevent SIGINT from causing the shell to exit. Also fixed a bug in command completion (basically I forgot to put -- in glob). With this modification, I'm now using tclsh as my login shell.
#! /usr/bin/env tclsh
# tclline: An attempt at a pure tcl readline.
# Use Tclx if available:
catch {
package require Tclx
# Prevent sigint from killing our shell:
signal ignore SIGINT
}
# Initialise our own env variables:
foreach {var val} {
PROMPT ">"
HISTORY ""
HISTORY_BUFFER 100
COMPLETION_MATCH ""
} {
if {![info exists env($var)]} {
set env($var) $val
}
}
foreach {var val} {
CMDLINE ""
CMDLINE_CURSOR 0
CMDLINE_LINES 0
HISTORY_LEVEL -1
} {
set env($var) $val
}
unset var val
array set ALIASES {}
set forever 0
# Resource & history files:
set HISTFILE $env(HOME)/.tclline_history
set RCFILE $env(HOME)/.tcllinerc
proc ESC {} {
return "\033"
}
proc shift {ls} {
upvar 1 $ls LIST
set ret [lindex $LIST 0]
set LIST [lrange $LIST 1 end]
return $ret
}
proc readbuf {txt} {
upvar 1 $txt STRING
set ret [string index $STRING 0]
set STRING [string range $STRING 1 end]
return $ret
}
proc goto {row {col 1}} {
switch -- $row {
"home" {set row 1}
}
print "[ESC]\[${row};${col}H" nowait
}
proc gotocol {col} {
print "\r" nowait
if {$col > 0} {
print "[ESC]\[${col}C" nowait
}
}
proc clear {} {
print "[ESC]\[2J" nowait
goto home
}
proc clearline {} {
print "[ESC]\[2K\r" nowait
}
proc getColumns {} {
set cols 0
if {![catch {exec stty -a} err]} {
regexp {rows \d+; columns (\d+)} $err -> cols
}
return $cols
}
proc prompt {{txt ""}} {
global env
set prompt [subst $env(PROMPT)]
set txt "$prompt$txt"
foreach {end mid} $env(CMDLINE_LINES) break
# Calculate how many extra lines we need to display.
# Also calculate cursor position:
set n -1
set totalLen 0
set cursorLen [expr {$env(CMDLINE_CURSOR)+[string length $prompt]}]
set row 0
set col 0
# Render output line-by-line to $out then copy back to $txt:
set found 0
set out [list]
foreach line [split $txt "\n"] {
set len [expr {[string length $line]+1}]
incr totalLen $len
if {$found == 0 && $totalLen >= $cursorLen} {
set cursorLen [expr {$cursorLen - ($totalLen - $len)}]
set col [expr {$cursorLen % $env(COLUMNS)}]
set row [expr {$n + ($cursorLen / $env(COLUMNS)) + 1}]
if {$cursorLen >= $len} {
set col 0
incr row
}
set found 1
}
incr n [expr {int(ceil(double($len)/$env(COLUMNS)))}]
while {$len > 0} {
lappend out [string range $line 0 [expr {$env(COLUMNS)-1}]]
set line [string range $line $env(COLUMNS) end]
set len [expr {$len-$env(COLUMNS)}]
}
}
set txt [join $out "\n"]
set row [expr {$n-$row}]
# Reserve spaces for display:
if {$end} {
if {$mid} {
print "[ESC]\[${mid}B" nowait
}
for {set x 0} {$x < $end} {incr x} {
clearline
print "[ESC]\[1A" nowait
}
}
clearline
set env(CMDLINE_LINES) $n
# Output line(s):
print "\r$txt"
if {$row} {
print "[ESC]\[${row}A" nowait
}
gotocol $col
lappend env(CMDLINE_LINES) $row
}
proc print {txt {wait wait}} {
# Sends output to stdout chunks at a time.
# This is to prevent the terminal from
# hanging if we output too much:
while {[string length $txt]} {
puts -nonewline [string range $txt 0 2047]
set txt [string range $txt 2048 end]
if {$wait == "wait"} {
after 1
}
}
}
rename unknown _unknown
proc unknown {args} {
global env ALIASES
set name [lindex $args 0]
set cmdline $env(CMDLINE)
set cmd [string trim [regexp -inline {^\s*[^\s]+} $cmdline]]
if {[info exists ALIASES($cmd)]} {
set cmd [regexp -inline {^\s*[^\s]+} $ALIASES($cmd)]
}
set new [auto_execok $name]
if {$new != ""} {
set redir ""
if {$name == $cmd && [info command $cmd] == ""} {
set redir ">&@ stdout <@ stdin"
}
if {[catch {
uplevel 1 exec $redir $new [lrange $args 1 end]} ret]
} {
return
}
return $ret
}
eval _unknown $args
}
proc alias {word command} {
global ALIASES
set ALIASES($word) $command
}
proc unalias {word} {
global ALIASES
array unset ALIASES $word
}
################################
# Key bindings
################################
proc handleEscapes {} {
global env
upvar 1 keybuffer keybuffer
set seq ""
set found 0
while {[set ch [readbuf keybuffer]] != ""} {
append seq $ch
switch -exact -- $seq {
"\[A" { ;# Cursor Up (cuu1,up)
handleHistory 1
set found 1; break
}
"\[B" { ;# Cursor Down
handleHistory -1
set found 1; break
}
"\[C" { ;# Cursor Right (cuf1,nd)
if {$env(CMDLINE_CURSOR) < [string length $env(CMDLINE)]} {
incr env(CMDLINE_CURSOR)
}
set found 1; break
}
"\[D" { ;# Cursor Left
if {$env(CMDLINE_CURSOR) > 0} {
incr env(CMDLINE_CURSOR) -1
}
set found 1; break
}
"\[H" -
"\[7~" -
"\[1~" { ;# home
set env(CMDLINE_CURSOR) 0
set found 1; break
}
"\[3~" { ;# delete
if {$env(CMDLINE_CURSOR) < [string length $env(CMDLINE)]} {
set env(CMDLINE) [string replace $env(CMDLINE) \
$env(CMDLINE_CURSOR) $env(CMDLINE_CURSOR)]
}
set found 1; break
}
"\[F" -
"\[K" -
"\[8~" -
"\[4~" { ;# end
set env(CMDLINE_CURSOR) [string length $env(CMDLINE)]
set found 1; break
}
"\[5~" { ;# Page Up }
"\[6~" { ;# Page Down }
}
}
return $found
}
proc handleControls {} {
global env
upvar 1 char char
upvar 1 keybuffer keybuffer
# Control chars start at a == \u0001 and count up.
switch -exact -- $char {
\u0003 { ;# ^c
# doExit
}
\u0008 -
\u007f { ;# ^h && backspace ?
if {$env(CMDLINE_CURSOR) > 0} {
incr env(CMDLINE_CURSOR) -1
set env(CMDLINE) [string replace $env(CMDLINE) \
$env(CMDLINE_CURSOR) $env(CMDLINE_CURSOR)]
}
}
\u001b { ;# ESC - handle escape sequences
handleEscapes
}
}
# Rate limiter:
set keybuffer ""
}
proc shortMatch {maybe} {
# Find the shortest matching substring:
set maybe [lsort $maybe]
set shortest [lindex $maybe 0]
foreach x $maybe {
while {![string match $shortest* $x]} {
set shortest [string range $shortest 0 end-1]
}
}
return $shortest
}
proc handleCompletion {} {
global env
set vars ""
set cmds ""
set execs ""
set files ""
# First find out what kind of word we need to complete:
set wordstart [string last " " $env(CMDLINE) \
[expr {$env(CMDLINE_CURSOR)-1}]]
incr wordstart
set wordend [string first " " $env(CMDLINE) $wordstart]
if {$wordend == -1} {
set wordend end
} else {
incr wordend -1
}
set word [string range $env(CMDLINE) $wordstart $wordend]
if {[string trim $word] == ""} return
set firstchar [string index $word 0]
# Check if word is a variable:
if {$firstchar == "\$"} {
set word [string range $word 1 end]
incr wordstart
# Check if it is an array key:
set x [string first "(" $word]
if {$x != -1} {
set v [string range $word 0 [expr {$x-1}]]
incr x
set word [string range $word $x end]
incr wordstart $x
if {[uplevel #0 "array exists $v"]} {
set vars [uplevel #0 "array names $v $word*"]
}
} else {
foreach x [uplevel #0 {info vars}] {
if {[string match $word* $x]} {
lappend vars $x
}
}
}
} else {
# Check if word is possibly a path:
if {$firstchar == "/" || $firstchar == "." || $wordstart != 0} {
set files [glob -nocomplain -- $word*]
}
if {$files == ""} {
# Not a path then get all possibilities:
if {$firstchar == "\[" || $wordstart == 0} {
if {$firstchar == "\["} {
set word [string range $word 1 end]
incr wordstart
}
# Check executables:
foreach dir [split $env(PATH) :] {
foreach f [glob -nocomplain -directory $dir -- $word*] {
set exe [string trimleft [string range $f \
[string length $dir] end] "/"]
if {[lsearch -exact $execs $exe] == -1} {
lappend execs $exe
}
}
}
# Check commands:
foreach x [info commands] {
if {[string match $word* $x]} {
lappend cmds $x
}
}
} else {
# Check commands anyway:
foreach x [info commands] {
if {[string match $word* $x]} {
lappend cmds $x
}
}
}
}
if {$wordstart != 0} {
# Check variables anyway:
set x [string first "(" $word]
if {$x != -1} {
set v [string range $word 0 [expr {$x-1}]]
incr x
set word [string range $word $x end]
incr wordstart $x
if {[uplevel #0 "array exists $v"]} {
set vars [uplevel #0 "array names $v $word*"]
}
} else {
foreach x [uplevel #0 {info vars}] {
if {[string match $word* $x]} {
lappend vars $x
}
}
}
}
}
set maybe [concat $vars $cmds $execs $files]
set shortest [shortMatch $maybe]
if {"$word" == "$shortest"} {
if {[llength $maybe] > 1 && $env(COMPLETION_MATCH) != $maybe} {
set env(COMPLETION_MATCH) $maybe
clearline
set temp ""
foreach {match format} {
vars "35"
cmds "1;32"
execs "32"
files "0"
} {
if {[llength [set $match]]} {
append temp "[ESC]\[${format}m"
foreach x [set $match] {
append temp "[file tail $x] "
}
append temp "[ESC]\[0m"
}
}
print "\n$temp\n"
}
} else {
if {[file isdirectory $shortest] &&
[string index $shortest end] != "/"} {
append shortest "/"
}
if {$shortest != ""} {
set env(CMDLINE) \
[string replace $env(CMDLINE) $wordstart $wordend $shortest]
set env(CMDLINE_CURSOR) \
[expr {$wordstart+[string length $shortest]}]
} elseif {$env(COMPLETION_MATCH) != " not found "} {
set env(COMPLETION_MATCH) " not found "
print "\nNo match found.\n"
}
}
}
proc handleHistory {x} {
global env
set hlen [llength $env(HISTORY)]
incr env(HISTORY_LEVEL) $x
if {$env(HISTORY_LEVEL) > -1} {
set env(CMDLINE) [lindex $env(HISTORY) end-$env(HISTORY_LEVEL)]
set env(CMDLINE_CURSOR) [string length $env(CMDLINE)]
}
if {$env(HISTORY_LEVEL) <= -1} {
set env(HISTORY_LEVEL) -1
set env(CMDLINE) ""
set env(CMDLINE_CURSOR) 0
} elseif {$env(HISTORY_LEVEL) > $hlen} {
set env(HISTORY_LEVEL) $hlen
}
}
################################
# History handling functions
################################
proc getHistory {} {
global env
return $env(HISTORY)
}
proc setHistory {hlist} {
global env
set env(HISTORY) $hlist
}
proc appendHistory {cmdline} {
global env
set old [lsearch -exact $env(HISTORY) $cmdline]
if {$old != -1} {
set env(HISTORY) [lreplace $env(HISTORY) $old $old]
}
lappend env(HISTORY) $cmdline
set env(HISTORY) \
[lrange $env(HISTORY) end-$env(HISTORY_BUFFER) end]
}
################################
# main()
################################
proc rawInput {} {
fconfigure stdin -buffering none -blocking 0
fconfigure stdout -buffering none -translation crlf
exec stty raw -echo
}
proc lineInput {} {
fconfigure stdin -buffering line -blocking 1
fconfigure stdout -buffering line
exec stty -raw echo
}
proc doExit {{code 0}} {
global env HISTFILE
# Reset terminal:
print "[ESC]c[ESC]\[2J" nowait
lineInput
set hlist [getHistory]
if {[llength $hlist] > 0} {
set f [open $HISTFILE w]
foreach x $hlist {
# Escape newlines:
puts $f [string map {
\n "\\n"
"\\" "\\b"
} $x]
}
close $f
}
exit $code
}
if {[file exists $RCFILE]} {
source $RCFILE
}
# Load history if available:
if {[llength $env(HISTORY)] == 0} {
if {[file exists $HISTFILE]} {
set f [open $HISTFILE r]
set hlist [list]
foreach x [split [read $f] "\n"] {
if {$x != ""} {
# Undo newline escapes:
lappend hlist [string map {
"\\n" \n
"\\\\" "\\"
"\\b" "\\"
} $x]
}
}
setHistory $hlist
unset hlist
close $f
}
}
rawInput
# This is to restore the environment on exit:
# Do not unalias this!
alias exit doExit
proc tclline {} {
global env
set char ""
set keybuffer [read stdin]
set env(COLUMNS) [getColumns]
while {$keybuffer != ""} {
if {[eof stdin]} return
set char [readbuf keybuffer]
if {$char == ""} {
# Sleep for a bit to reduce CPU time:
after 40
continue
}
if {[string is print $char]} {
set x $env(CMDLINE_CURSOR)
if {$x < 1 && [string trim $char] == ""} continue
set trailing [string range $env(CMDLINE) $x end]
set env(CMDLINE) [string replace $env(CMDLINE) $x end]
append env(CMDLINE) $char
append env(CMDLINE) $trailing
incr env(CMDLINE_CURSOR)
} elseif {$char == "\t"} {
handleCompletion
} elseif {$char == "\n" || $char == "\r"} {
if {[info complete $env(CMDLINE)] &&
[string index $env(CMDLINE) end] != "\\"} {
lineInput
print "\n" nowait
uplevel #0 {
global env ALIASES
# Handle aliases:
set cmdline $env(CMDLINE)
set cmd [string trim [regexp -inline {^\s*[^\s]+} $cmdline]]
if {[info exists ALIASES($cmd)]} {
regsub -- "(?q)$cmd" $cmdline $ALIASES($cmd) cmdline
}
# Perform glob substitutions:
set cmdline [string map {
"\\*" \0
"\\~" \1
} $cmdline]
# Don't substitute * and ~ in braces:
foreach x [regexp -inline -all -indices {{.*?}} $cmdline] {
foreach {i n} $x break
set s [string range $cmdline $i $n]
set s [string map {
"*" \0
"~" \1
} $s]
set cmdline [string replace $cmdline $i $n $s]
}
while {[regexp -indices \
{([\w/\.]*(?:~|\*)[\w/\.]*)+} $cmdline x]
} {
foreach {i n} $x break
set s [string range $cmdline $i $n]
set x [glob -nocomplain -- $s]
# If glob can't find anything then don't do
# glob substitution, pass * or ~ as literals:
if {$x == ""} {
set x [string map {
"*" \0
"~" \1
} $s]
}
set cmdline [string replace $cmdline $i $n $x]
}
set cmdline [string map {
\0 "*"
\1 "~"
} $cmdline]
# Run the command:
catch $cmdline res
if {$res != ""} {
print "$res\n"
}
# Append HISTORY:
set env(HISTORY_LEVEL) -1
appendHistory $env(CMDLINE)
set env(CMDLINE) ""
set env(CMDLINE_CURSOR) 0
set env(CMDLINE_LINES) {0 0}
}
rawInput
} else {
set x $env(CMDLINE_CURSOR)
if {$x < 1 && [string trim $char] == ""} continue
set trailing [string range $env(CMDLINE) $x end]
set env(CMDLINE) [string replace $env(CMDLINE) $x end]
append env(CMDLINE) $char
append env(CMDLINE) $trailing
incr env(CMDLINE_CURSOR)
}
} else {
handleControls
}
}
prompt $env(CMDLINE)
}
tclline
fileevent stdin readable tclline
vwait forever
doExitTo have tclline automatically available when you start tclsh add the following to your .tclshrc file:
if {$tcl_interactive} {
source /path/to/your/tclline.tcl
}rdt Nice idea, but my question is: Is the if test really necessary? Isn't .tclshrc only read when tclsh is running interactively? Next question: How about adding this into the interactive part of init.tcl ?
rdt Another question: I can't really see what you changed in the unknown proc as I have 8.4 and tkdiff on the two procs shows a lot of change in the 8.4 version. So what did you change/add to that proc for your version?
slebetman: Only one simple thing: I removed the info level and info script test to allow unknown to call auto_execok from any level after the shell sources tclline. Try running the commands below in an interactive session of tclsh and see if the output makes sense. If it does, that's probably the only editing you need:
set x [info body unknown]
set x [regsub -all {if \{.{0,5}info level.{0,10}?&&} $x "if {"]
set x [regsub -all {if \{.{0,5}info script.{0,10}?&&} $x "if {"]
set x "proc unknown {[info args unknown]} {$x}"rdt 2006.07.13 - With some changes, that is what I did to use the 8.4 unknown. Is there some reason that you did not use the history.tcl present in the distribution or is not present in yours? I made use of it myself.
slebetman: I didn't know how to use it. I thought that history would always take the last executed command which also means the code in tclline itself. Now that I've tried it I see that's not really the case. But I still prefer my implementation since it removes duplicate events (This have been my pet peeve with almost all implementations of history, from tcl to bash to DOSKEY). Besides, an implementation of history is really is almost nothing. It is merely an lappend to a list.
rdt 2006.07.14 - I understand what you are saying, however: history can be used in at least two ways. Suppose that you need to redo a command from much earlier but don't remember the id. You 'history | grep <something_unique>' and discover that it was 987. You can then '!987' and redo it. You do a few commands and then say '!-3' to redo it again. If you don't put duplicates in the list (or keep up with all the id's for a command), then one of these capabilities gets lost.
I think what you really want is to keep all the items in the list but be able to display the list in several different ways: a) 'history' for the default full list, b) 'history -20' for the 20 most recent, c) 'history -b' for the list without duplicates, but show the first & last id, and d) 'history <some_re>' to show only those items that match <some_re>.
SRIV I prefer the current optimized history. Its quick and simple and conforms to the 80/20 rule. A grep-able history is nifty, but If I need that, I shouldn't be doing work in a single console anway. I'd switch my devel work to a gui workstation.
slebetman My implementation of history is grep-able anyway (well, regexp-able at least). It's just a list stored in an environment variable!
foreach x $env(HISTORY) {if {[regexp $something_unique $x]} {puts $x}}The only thing I don't have is history substitution (haven't implemented because frankly I've never used it). I believe Tkcon does it via unknown which means we can implement it too.
rdt - So you are saying with this implementation, you can't do things '!2', or '!!', or '!-2' which are already implemented in unknown?
jcolburn - What about putting all this into a namespace? I'm taking a stab at it. Also, I added some emacs ctrl key shortcuts
proc handleControls {} {
global env
upvar 1 char char
upvar 1 keybuffer keybuffer
# Control chars start at a == \u0001 and count up.
switch -exact -- $char {
\u0001 { ;# ^a
set env(CMDLINE_CURSOR) 0
}
\u0002 { ;# ^b
if {$env(CMDLINE_CURSOR) > 0} {
incr env(CMDLINE_CURSOR) -1
}
}
\u0004 { ;# ^d
set env(CMDLINE) [string replace $env(CMDLINE) \
$env(CMDLINE_CURSOR) $env(CMDLINE_CURSOR)]
}
\u0005 { ;# ^e
set env(CMDLINE_CURSOR) [string length $env(CMDLINE)]
}
\u0006 { ;# ^f
if {$env(CMDLINE_CURSOR) < [string length $env(CMDLINE)]} {
incr env(CMDLINE_CURSOR)
}
}
\u0007 { ;# ^g
set env(CMDLINE) ""
set env(CMDLINE_CURSOR) 0
}
\u000b { ;# ^k
set env(YANK) [string range $env(CMDLINE) [expr {$env(CMDLINE_CURSOR) } ] end ]
set env(CMDLINE) [string range $env(CMDLINE) 0 [expr {$env(CMDLINE_CURSOR) - 1 } ]]
}
\u0019 { ;# ^y
if { [ info exists env(YANK) ] } {
set env(CMDLINE) \
"[string range $env(CMDLINE) 0 [expr {$env(CMDLINE_CURSOR) - 1 } ]]$env(YANK)[string range $env(CMDLINE) $env(CMDLINE_CURSOR) end]"
}
}
\u000e { ;# ^n
handleHistory -1
}
\u0010 { ;# ^p
handleHistory 1
}
\u0003 { ;# ^c
# doExit
}
\u0008 -
\u007f { ;# ^h && backspace ?
if {$env(CMDLINE_CURSOR) > 0} {
incr env(CMDLINE_CURSOR) -1
set env(CMDLINE) [string replace $env(CMDLINE) \
$env(CMDLINE_CURSOR) $env(CMDLINE_CURSOR)]
}
}
\u001b { ;# ESC - handle escape sequences
handleEscapes
}
}
# Rate limiter:
set keybuffer ""
}Bezoar - Added the Control-Y (Yank) and updated Ctrl-K (kill to end of line ) for emacs bindings
alsterg - Corrected a small mistake where:
if {[llength $match]} {was used instead of:
if {[llength [set $match]]} {HGC I collected the code above a few months back, found it to be quite useful - then made a few changes to my version:
My question: is this of interest to anyone? If so - I'd be happy to post it back here. If not - no problem.
slebetman The usual rule of the wiki is: go ahead and post it. I'd suggest creating a new page Pure-tcl readline2 (like how I did with the pure tcl text editor) and post your code there. I'd definitely be interested in it being namespaced properly (the next step is to run commands in a slave interp - like how tkcon does it - but that will have to wait for now).
HGC Done. Note that there is some dead code in the new version; I didn't completely remove the previous 'history' implementation, for example. (Further cleanup is possible.) Further isolation into a slave interp is a good idea.
ZB 2010-01-03 If tclline.tcl can replace the "usual" bash (or whichever other shell), I would to make a feature suggestion, that could help us to dispose of all that "exec magic":
I think, it could be useful to equip it with ability to recognize "on its own" proper interpreter, looking just at the file extension. Five conditions should be met to trigger such behaviour: if the file has "eXecute" flag set, if the filename has any extension at all, if it's "pure text" file, if there isn't in its first line interpreter choosen explicitly already, and if the interpreter for the files of the given extension is present in the system installation.
For example:
Actually, why it shouldn't figure out by itself: "the file has .tcl extension, so obviously we need tclsh to execute" - quite on its own?