当行包含变量时，如何用单个命令替换文件中的一行文本？

Question

I have a script called script.sh which has the contents

export HELLO=$WORLD

I want to change it using a single command to

export HELLO=${WORLD:2:3}

I'm attempting to use the sed command but i'm new to linux and can't quite get it right. Here's what I have

sed -i 's/export HELLO=$WORLD/export HELLO=${WORLD:2:3}' script.sh

How should this line be written to replace the text correctly?

Answer 1

You just missed a / at the very end:

sed -i 's/export HELLO=$WORLD/export HELLO=${WORLD:2:3}/' script.sh
                                                       ^
                                       this / is missing

Answer 2

The $ is a special symbol that means end of line, also as @yvesonline points out you are missing the trailing /. This is how I would do it:

sed -i 's/\(export HELLO=\$\)\(WORLD\)/\1{\2:2:3}/' script.sh