在bash中查找并替换变量

Question

I am using bash and I was wondering if there is a nice way to do a find and replace on a file using bash. In my case I want to turn a placeholder variable into the orignal variable, working with any number of different variables. For example:

"$PLACEHOLDER_ABC" -> $ABC 
"$PLACEHOLDER_123" -> $123 
"$PLACEHOLDER_qwe" -> $qwe

I am not sure where to start, should I be using find, sed, a while loop, or all of the above?

Answer 1

Something like

sed 's/\$PLACEHOLDER_/\$/g' file

would remove PLACEHOLDER_ everywhere it is found after a dollar sign, effectively truncating the parameter expansion where it occurs.

Answer 2

You may want to have a look at "m4" the macro processor. The manpages are here . It is included in most Linux/Unix distros.

Here is a little example:

define(`hello', `Hello, World')
hello, welcome to m4!

If we run this file through m4 with the command

m4 sample.m4 > sample.txt

it produces the following output:

Hello, World, welcome to m4!

Answer 3

查找文件名-exec sed -i's / \\ $ PLACEHOLDER _ / \\ $ / g'{} \\;