Differences between single quotes and double quotes

Source: Internet
Author: User
Differences between single quotes and double quotes-Linux general technology-Linux technology and application information. Variables can be referenced in double quotation marks, which can be omitted simply.
The $ symbol in single quotes is used by common characters.
A = B
Echo "$"
B
Echo '$'
$
One problem is whether to use single or double quotes When referencing location variables and pre-defined variables. $1-$9. $0 is double quotes. I have confirmed it.
However, an awk command for filtering text outputs the content of a specified segment.
Awk '{print $2, $4 }'
How does the content in the upper braces use the location variable in single quotes?
How to Understand /?
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