Re: #!shebang

[#!microsuxx]

u can replace eval with declare , or any other builtin i think ..

On Wed, Nov 20, 2024, 1:25 PM Greg Wooledge <greg@wooledge.org> wrote:

> On Wed, Nov 20, 2024 at 10:19:25 +0100, lacsaP Patatetom wrote:
> > I currently store my configuration like this in `configuration.qemu` :
> > ```
> > -argument
> >
> > - argument -option
> >
> > -etc...
> > ```
> >
> > and I call `qemu` like this and it works as expected :
> > `$ qemu $(<configuration.qemu)`
>
> For the record, this is not "safe" in general.  It uses the shell's
> default word splitting to separate the arguments, and therefore it
> will fail if any of your arguments have spaces in them.
>
> hobbit:~$ cat z
> -foo
> -file="a file with spaces"
> -bar
> hobbit:~$ args $(<z)
> 6 args: <-foo> <-file="a> <file> <with> <spaces"> <-bar>
>
> Now, maybe it's impossible for qemu to receive an argument that contains
> whitespace, and therefore this hack works for qemu -- I don't know.
>
> What I do know is that there *will* be other programs for which it can
> fail.  A filename argument may contain whitespace, for example.  Or
> you may call "make" with an argument like CFLAGS="-g -O2" and so on.
>
> What you're doing is more suited to eval.  As long as you recognize
> that your "configuration file" is really a shell script fragment, with
> real consequences if it contains command substitutions and so on, then
> you might try this:
>
> hobbit:~$ eval args "$(tr '\n' ' ' <z)"
> 3 args: <-foo> <-file=a file with spaces> <-bar>
>
> All of the warnings you've heard about eval apply here.  If you're
> adding other argument constructors to the same command, then eval
> will apply to them as well.  Be very sure of what you're doing if
> you choose this route.
>
> So, your next question is probably going to be "how do I add comments
> to this?"  Before I answer that, let's explore another approach.  We'll
> start with the same file:
>
> hobbit:~$ cat z
> -foo
> -file="a file with spaces"
> -bar
> hobbit:~$ eval "a=( $(<z) )"; args "${a[@]}"
> 3 args: <-foo> <-file=a file with spaces> <-bar>
>
> In this version, I'm populating an array using the file's contents.
> The eval command expands out to this:
>
> a=( -foo
> -file="a file with spaces"
> -bar )
>
> There's no need to translate the newlines in this case, as they are
> allowed within an array assignment.  In fact, so are comments.  Let's
> add some comments to our input file:
>
> hobbit:~$ cat z
> -foo
> # a whole line comment
> -file="a file with spaces"
> -bar # an inline comment
> -q
> hobbit:~$ eval "a=( $(<z) )"; args "${a[@]}"
> 4 args: <-foo> <-file=a file with spaces> <-bar> <-q>
>
> I believe that does all the things you require.  It may rule out some
> trickery that you were hoping to achieve with a shebang, but I don't
> care about that.  I prefer to give you an approach that won't break.
>
> #!/bin/bash
> eval "args=( $(<configuration.qemu) )"
> qemu "${args[@]}"   # maybe with exec
>
> There, nice and clean.  Or as clean as your configuration.qemu file is.
>
>