Version 25 of auto_execok

Updated 2013-01-23 02:14:35 by RLE

auto_execok is one of several commands documented at http://www.tcl.tk/man/tcl8.5/TclCmd/library.htm

It determines whether an executable file, or shell builtin, exists, based on its single argument. See auto_reset for info on how to clean up after an auto_execok's caching.


On Unixy platforms, scripts may get away with exec [auto_execok $progname] $firstarg ..., but this is in general wrong, since auto_execok always returns a list of arguments for exec!

Canonical example usage:

    eval exec [auto_execok myCommand] [list $arg1 "Some text" $arg3]

or, with 8.5 [L1 ],

    exec {*}[auto_execok myCommand] $arg1 "Some text" $arg3

[Explain why this is better than $::env(COMSPEC), cmd.exe, ...]

LES on September 16, 2004: auto_execok is better than $::env(COMSPEC) and cmd.exe? Get outta here... :-)


To demonstrate why [eval] was required before 8.5:

 % auto_execok start
 C:/WINNT/system32/CMD.EXE /c start
 % exec [auto_execok start] http://wiki.tcl.tk
 couldn't execute "C:\WINNT\system32\CMD.EXE \c start": invalid argument
 % eval exec [auto_execok start] http://wiki.tcl.tk
 % # success

Note that if any arguments to "start" have spaces (or other white space, or other syntactically-privileged characters) in them, you have to list-protect them from eval

 % set mydoc "My document.doc"
 % eval exec [auto_execok start] $mydoc
 % # msword may complain about being unable to find "My" and "document.doc"'
 % eval exec [auto_execok start] \"\" [list $mydoc]; # should be more successful
 % # Dont't forget the '\"\"' otherwise "My document.doc" is used as the window-titel for
 % # a DOS-shell.

Other wiki pages that deal with similar issues include exec, exec ampersand problem, invoking browsers, clear screen. See also COMSPEC.