Usage of shebang in file header: is there any option to pass multiple arguments in shebang

Question

I am using a different namespace for my python file execution. using a shebang/hashbang, to execute this script (/bin/bash -c ).

problem faced is shebang only accepts a single argument. even if i pass multiple args its treating it as a single string.

shebang used: #!/sbin/ip netns exec tmp <executable>

Experiment:

1. single executable using : #!/sbin/ip

   Object " tmp" is unknown, try "ip help".
   

2. one arg shebang in tmp : #!/sbin/ip netns

   $/bin/bash -c  tmp
   Command "tmp" is unknown, try "ip netns help".
   

3. with two arg shebang used in tmp: #!/sbin/ip netns exec

   $/bin/bash -c  tmp
   Object "netns exec" is unknown, try "ip help".
   

   • its picking "netns exec" as a single argument

4. full cmd used

   shebang used in tmp : #!/sbin/ip netns exec global python

   $/bin/bash -c  tmp
   Object "netns exec global python" is unknown, try "ip help".
   

Is there any way to pass multiple argumenets to shebang executable other than chaining files.

Answer 1

Linux (and other OSs I believe) only split the shebang string once, at the first whitespace. So you can only ever pass one argument.

When you do #!/sbin/ip netns exec tmp <executable>, ip sees one argument string: netns exec tmp <executable> (including spaces).

But GNU env added the -S option for splitting shebang arguments. It's also available on FreeBSD env. But not busybox env.

So if you launch your interpreter using env -S:

#!/usr/bin/env -S command -a -b -c

env will split the three arguments on white space, and pass them to command. env of course is seeing the single argument -S command -a -b -c, but it can parse this.

I don't know enough about namespaces to know if this is a good idea, but it seemed to work for me:

$ sudo ip netns add test
$ sudo ip netns identify
# (empty)

$ cat /tmp/netns-shebang-test
#!/usr/bin/env -S ip netns exec test bash

echo "$BASH_VERSION"
echo "$0"
ip netns identify

$ sudo /tmp/netns-shebang-test
5.1.16(1)-release
/tmp/netns-shebang-test-script
test

I'm showing bash, but it also worked with a similar python script. I will repeat that I don't know enough about namespaces to know if this is a good approach or not.