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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.

Gordon Davisson
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Nishad C M
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  • Interpretation of the shebang depends on the OS (I think generally the kernel controls it). What OS are you using? BTW, I tried to clean up the formatting & spelling of your question, please make sure I didn't make any errors (see [this](https://meta.stackoverflow.com/questions/251361/how-do-i-format-my-code-blocks) for info about code/literal section formatting). – Gordon Davisson May 05 '22 at 05:10

1 Answers1

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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.

dan
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