tcl spawn sftp not working - tcl

Question

I am trying to run a very simple tcl script
package require Expect
spawn sftp user#host
the error I get is
The system cannot find the file specified.
while executing
"spawn sftp user#host"
The only reason I see it's that sftp path should be specified somehow. I call this from a batch script and I've also tried changing the directory to sftp location before calling the script but the error is still the same.

Answer 1

By far the most likely cause of the issue here is that the sftp program is not in a directory that is on your PATH. The concept is almost the same across platforms, but with some minor niggles.
Working with the Unix PATH
Check to see if sftp is available in a PATH-known directory by typing:
which sftp
At your shell prompt. It should respond with the location of the sftp program, but if it isn't found then you get no response at all. If it isn't found, you'll need to find it yourself and add its location (strictly, the directory that contains the program) to the PATH. Find the program with something like:
locate sftp
Or (very slow!):
find / -name sftp -print
To append a directory to the PATH, do this in your shell:
PATH=$PATH:/the/dir/to/append
You can add a directory within the Expect script too (as long as it is before the spawn, of course!):
append env(PATH) : /the/dir/to/append
Working with the Windows PATH
On Windows, use Windows Search (Windows+F IIRC) and look for a file called sftp.exe (there's also a command line search tool, but I forget how to use it).
With the Windows PATH, a little more care is required:
append env(PATH) ";" {C:\the\dir\to\append}
# Or this...
append env(PATH) ";" [file nativename C:/the/dir/to/append]
Which is to say, the Windows PATH uses a different separator character (because : is used for separating drive names from directory parts) and the native name of the directory must be used, rather than the somewhat-more-convenient forward-slash variation (the backslashes interact with Tcl's syntax, hence the {braces}). Forward-slashes can be used provided you use file nativename to convert before appending, as in my second version.
Some Tcl Techniques that can Help
You can use the Tcl command auto_execok to find out whether a program is on your PATH or not. For example:
puts [auto_execok sftp]
However, for some commands (notably start on Windows) you get a more complex response; the command really exists as part of the code that supports interactive Tcl usage, describing how to run some external program which can sometimes be a lot more complex than it appears to be at first glance. Still, it approximates to a cross-platform version of which as listed in the beginning of this answer...
Tcl 8.6 provides $tcl_platform(pathSeparator) variable as a way to get the PATH element separator character (a : or ;, depending on platform). Probably doesn't help you though, as 8.6 hasn't yet been distributed as widely as previous versions.