auto_execok, a command in the Tcl library, determines whether an executable file, or shell builtin, exists, based on its single argument. See auto_reset for info on how to clean up the cache of auto_execok.
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:
exec {*}[auto_execok myCommand] $arg1 {Some text} $arg3[Explain why this is better than $::env(COMSPEC), cmd.exe, ...]
LES 2004-09-16: 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] https://wiki.tcl-lang.org couldn't execute "C:\WINNT\system32\CMD.EXE \c start": invalid argument % eval exec [auto_execok start] https://wiki.tcl-lang.org % # 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.