Specifying a generic interpreter for a program like expect?

Question

I am writing expect script which can be used on mulple operating systems but the problem is

i can't use #!/usr/bin/expect evreywhere so instead i tried to do

 #!`which expect`

at the top but it failed

[sesiv@itseelm-lx4151 ~]$ ./sendcommand
-bash: ./sendcommand: `which: bad interpreter: No such file or directory

any solution for this.

Solution 1

One trick that mostly works (for perl, python, php interpreters, and probably others):

#!/usr/bin/env expect

I think env is always in /usr/bin/. A lot of interpreters can run that way now. Other hacks used to exist, but weren't understandable, or weren't all that portable.

Solution 2

I suggest

#!/bin/sh
expect_path="$(which expect)"
"$expect_path" "$0" "$@"

I hope this works; I am not familiar with the differences between bash and sh.

Comments

[Hauke Laging]

Is there anything you can use everywhere, /bin/bash e.g.?

[Ezequiel]

i am not sure about this but, i think most standard OS will have /bin/sh say AIX,solaris,linux,redhat,suse,HP

[Gilles 'SO- stop being evil']

See also How can I have more than one possibility in a script's shebang line?

[Jpark822]

This is also the portable way to run bash (#!/usr/bin/env bash, which will work even when your bash is in /usr/bin/local/bash or elsewhere).

[Keith]

You can also expand on this by putting a check that it was actually found, and using exec before the path.