如何在Bash中用引号引起来的字符串中使用环境变量

我在bash脚本中尝试了以下各种形式:

I've tried various forms of the following in a bash script:

#!/bin/bash
svn diff $@ --diff-cmd /usr/bin/diff -x "-y -w -p -W $COLUMNS"

但是我无法正确地扩展COLUMNS环境变量的语法.

But I can't get the syntax to correctly expand the COLUMNS environment variable.

我尝试了以下各种形式:

I've tried various forms of the following:

svn diff $@ --diff-cmd /usr/bin/diff -x '-y -w -p -W $COLUMNS'

和

svn diff $@ --diff-cmd /usr/bin/diff -x '-y -w -p -W ${COLUMNS}'

和

eval svn diff $@ --diff-cmd /usr/bin/diff -x "-y -w -p -W $COLUMNS"

建议?