Re: cope with spaces in an environment variable

[Kerin Millar]

On Mon, 19 Jun 2023 12:09:35 +0900
Masahiro Yamada <masahiroy@kernel.org> wrote:

> On Mon, Jun 19, 2023 at 4:22 AM Kerin Millar <kfm@plushkava.net> wrote:
> >
> > On Mon, 19 Jun 2023 03:37:24 +0900
> > Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > > Hi.
> > >
> > > I'd like to know the proper handling of an environment variable
> > > when the value may contain spaces (with quoting).
> > >
> > > Here is my question.
> > >
> > > You have the environment variable 'CC', which contains a compiler path.
> > >
> > > For example, how to write a shell script to
> > > compile a C file with ${CC}?
> >
> > By shell script, do you mean that POSX sh is the intended target?
> 
> 
> Thanks for the pointers, all guys.
> 
> 
> 
> Ideally, working on POSIX sh would be nice.

If I had to do this, I would not be inclined to use eval. Greg has already 
stressed this point. The least-bad options (by my reckoning) are shown below.

# Parse newline-separated arguments out of a string. No shell code injection.
# Obviously, it cannot support arguments containing newlines. Allows for the
# positional parameters to be preserved, though this example does not.
printf '%s\n' "$CC_ARGS" | {
        set -- cc
        while IFS= read -r word; do
                set -- "$@" "$word"
        done

        "$@" foo.c
}

# Let xargs(1) do the parsing. Requires understanding - and acceptance - of
# the behaviour of its parser, along with its limitations. Has rudimentary
# quote handling. Tolerable for simple cases, where its input is tightly 
# controlled and predictable in advance. Doesn't scale beyond that. No code
# injection either. Makes it a little more expensive to call cc.
CC() {
        printf %s "$CC_ARGS" | xargs -E '' cc
}

CC foo.c

-- 
Kerin Millar