Bash变量的后期绑定，同时保留空格

Question

I'm trying to do late binding of the directories where my packages are in a make command. Basically, WITH_OPTIONS command line contains a space-separated list of link options similar to a configure script. The problem is the directories are bound late, after the command line to this script is parsed, so I need to eval the template string to get the right variable bindings. The closest I can come with so much googling and reading of the Bash FAQ, especially article 50 is something like:

MAKE_INSTALL="make install"
TEMPLATE=('--first=$a' '--second=$b' '--third=$a')

# Parse Parameters
a=/first/path
b=/second/path
TEMPLATE_REPL=$( eval echo ${TEMPLATE[@]} )
CMD="$MAKE_INSTALL WITH_OPTIONS=\"$TEMPLATE_REPL\""
$CMD

What I'd expect $CMD to contain would be a string with one command and 2 parameters:

make install WITH_OPTIONS="--first=/first/path --second=/second/path --third=/first/path"

However, I can't get bash to keep the part in quotes together, so it keeps parsing it as:

make install 'WITH_OPTIONS="--first=/first/path' '--second=/second/path' '--third=/first/path"'

Which is obviously totally wrong and will cause a bad command line when executed.

What am I missing? How do I preserve the bit between the quotes as one parameter, not 3?

Answer 1

Why not simply make TEMPLATE a string:

TEMPLATE='--first=$a --second=$b --third=$a'
$ a=/first/path
$ b=/second/path
$ eval echo $TEMPLATE
--first=/first/path --second=/second/path --third=/first/path

Answer 2

MAKE_INSTALL="make install"
TEMPLATE='--first=$a --second=$b --third=$a'

# Parse Parameters
a=/first/path
b=/second/path
CMD="$MAKE_INSTALL WITH_OPTIONS=\"$TEMPLATE\""
eval $CMD

As ennuikiller pointed out, Arrays are unnecessary but because Johnathan Leffler points out make, the command I'm attempting to execute, is the thing ignoring the double quotes, the correct approach is to call eval when executing $CMD. This will require a bit of work to fit into my script but I think that's the basic solution to the problem as I set it up. Although I can't give ennuikiller full credit for this solution I'm happy to at least given you a +1 in your rating.

(Ed: Because the second eval is required, the first eval can be removed.)

Answer 3

Here's a generic example of using late binding in bash scripts, with variables (variable substitution):

#!/usr/bin/env bash

A_tmp="echo -n Late binding: \$B !!!"             ## note the slash before $
B="test string"

A=`eval $A_tmp`

echo $A

This script prints:

Late binding: test string !!!