auto_execok is one of several ''[command%|%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 [http://wiki.tcl.tk/10630], ====== 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]. <> Tcl syntax | Arts and crafts of Tcl-Tk programming | Command