Nesting quotes in bash

I want to something like this in bash:

 alias foo='bar="$(echo hello world | grep \"hello world\")"; echo $bar;'; foo

Expected output: hello world

Ouput: grep: world": No such file or directory

• The outer quotes have to be single quotes, with double qu开发者_如何学Gootes $bar would be empty.

• The next quotes have to be double quotes, with single quotes $() wouldn't expand.

• The inner quotes could be both type of quotes, but single quotes doesn't allow single quotes inside of them.

How to I achieve this?

The stuff inside $() represents a subshell, so you are allowed to place un-escaped double quotes inside

alias foo='bar="$(echo testing hello world | grep "hello world")"; echo "$bar"'

It's a bit unclear what "something like this" means, but the simplest way to achieve what seems to be the point here is a simple function:

foo() {
    echo 'hello world' | grep 'hello world'
}
foo

• There's no need for an intermediate variable assignment (it will be lost anyway).
• Functions are generally preferred over aliases because of more flexibility (parameter handling) and readability (multiple lines; less escaping).
• Always use the simplest solution which could possibly work.

Escape the spaces

alias foo='bar="$(echo hello world | grep hello\ world)"; echo $bar;'

The double quotes around $() are not necessary:

alias foo='bar=$(echo hello world | grep "hello world"); echo $bar;'
foo

# Output:
hello world