This page serve as an anchor to lead people to the most frequent way to detect availability of executables:  [auto_execok]

There actually is a reason to prefer detecting executables using [exec] instead of [auto_execok], that's when the executable returned by [auto_execok] actually is not executable. This is almost certainly a bug of the execution environment, but at least it bugs [Cygwin], thus someone might want to use the following workaround.

Cygwin have a hybrid mix of [win32] tcl/tk and their [POSIX] environment. Let's say we detect availability of `cdrecord`, [auto_execok] would return a path which is a symlink, but tcl/tk script running on cygwin's win32 tcl engine cannot invoke symlinks, thus script fail when invoked.

A workaround is to actually run the target executable to do a simple thing, like printing its version number. The code is a bit complicated because you need to worry if version number is written on [stderr], resulting failed [exec]. Thus a second check at $::[errorCode] is necessary:

======
if {![catch {exec cdrecord -version}] || [lindex $::errorCode 0] eq "NONE"} {
    puts stderr "'cdrecord' is available"
}
======

<<categories>>Interprocess Communication