Emulating sudo's behaviour with su

Question

I'm trying to write a wrapper around su to make it more like sudo, so that su_wrapper foo bar baz == su -c "foo bar baz".

However, I'm not sure how to approach this problem. I came up with this:

su_wrapper ()
{
  su -c "$@"
}

However, in the above, only a single argument can be there; this fails with multiple arguments (as su sees them as its own arguments).

There's also another problem: since the argument is passed through the shell, I think I must explicitly specify the shell to avoid other problems. Perhaps what I want to do could be expressed in pseudo-bash(!) as su -c 'bash -c "$@"'.

So, how could I make it accept multiple arguments?

@shx2, I'm really tired of having to quote things when using su, and I'm not allowed to use sudo on these boxes. — , Jun 21 '14 at 10:36
(for the record, it isn't clear to me why people voted to close. this is about general computing. `su` and `sudo` are tools used by programmers.) — shx2, Jun 21 '14 at 10:37

score 2 · Accepted Answer · answered Jun 21 '14 at 18:11

2

Use printf "%q" to escape the parameters so they can be used as string input to your function:

su_wrapper() {
    su -s /bin/bash -c "$(printf "%q " "$@")"
}

Unlike $*, this works even when the parameters contain special characters and whitespace.

answered Jun 21 '14 at 18:11

that other guy

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score 1 · Answer 2 · answered Jun 21 '14 at 11:13

1

You need $* and not $@:

su_wrapper() {
    local IFS=' '
    su -c "$*"
}

See the Special Parameters section in the Bash Reference Manual for the difference between $* and $@.

I added local IFS=' ' just in case IFS is set to something else (after reading what $* does, it should be clear why you want to make sure that IFS is set to a space).

answered Jun 21 '14 at 11:13

gniourf_gniourf

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This would fail for `su_wrapper ls "foo bar"` and `su_wrapper find . -name '.*'` – that other guy Jun 21 '14 at 18:13
@thatotherguy you're right, but you can always properly quote the arguments to obtain what you want. – gniourf_gniourf Jun 21 '14 at 18:23
But you have to quote them twice, unlike sudo. – that other guy Jun 21 '14 at 18:27
@thatotherguy right, but the counterpart is that redirection is much easier: `su_wrapper "ls > file"`, no need to fiddle with `tee` or similar artifice. So what you lose on one side, you gain it on the other side. Choose your side `:)`. – gniourf_gniourf Jun 21 '14 at 18:29
If you want to pass in an entire, quoted command, why not just use su? – that other guy Jun 21 '14 at 18:33

Emulating sudo's behaviour with su

2 Answers2