Re: Proposal to add /usr/bin/shquote

[David Laight <david%l8s.co.uk@localhost>]

On Fri, Sep 05, 2008 at 09:38:52PM +0200, Alan Barrett wrote:
> I often find the need, in shell scripts, to escape arguments to be
> passed to other shell commands.  I'd like to add a /usr/bin/shquote
> command as a simple wrapper around shquotev(3) to do this.
> 
> Sample usage:
> 
>       $ shquote foo bar
>       'foo' 'bar'
>       $ set -- -foo bar "arg with spaces" "don't panic" '"Help!"'
>       $ echo "$#"
>       5
>       $ echo "$4"
>       don't panic
>       $ list="$( shquote "$@" )"
>       shquote: unknown option -- f
>       Usage: shquote [--] [arg ...]
>       $ list="$( shquote -- "$@" )"
>       $ echo "$list"
>       '-foo' 'bar' 'arg with spaces' 'don'\''t panic' '"Help!"'
>       $ eval "set -- $list"
>       $ echo "$#"
>       5
>       $ echo "$4"
>       don't panic
> 
> --apb (Alan Barrett)

I don't see the problem ?
You just need to understand when the shell does 'field splitting'.
Try running:

show_args() {
    name="$1"
    shift
    echo $name: $# args
    while [ -n "$1" ]
    do
        echo "    $1"
        shift
    done
}
set -- -foo bar "arg with spaces" "don't panic" '"Help!"'
echo "$#"
echo "$4"
show_args '$*' $*
show_args '"$*"' "$*"
show_args '$@' $@
show_args '"$@"' "$@"
show_args '$1-$4' $1 $2 $3 $4
show_args '"$1"-"$4"' "$1" "$2" "$3" "$4"
(IFS=; show_args '$1-$4 (no IFS)' $1 $2 $3 $4)

In general shell scripts ought to put most $foo expansions inside "".

        David

-- 
David Laight: david%l8s.co.uk@localhost